RF REPEATER

COMMERCIALIZATION

Team Members: Sean Kainuma Elaine Owens

Bryan Hammer Joey Zeledon

Sponsor: David Perlman

Mentors: Dr. Phillips

Dr. Venkataraman

Coordinator: Prof.Slack

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1 INTRODUCTION ...........................................................................................5

1.1 Desired functionality of RF repeater (Final product) ................................................................. 5

1.2 Our objectives................................................................................................................................. 5

1.3 Our Budget ..................................................................................................................................... 5

2 NEEDS AND REQUIREMENTS:...................................................................6

2.1 Range extension.............................................................................................................................. 6

2.2 Power............................................................................................................................................... 6

2.3 Cost.................................................................................................................................................. 6

2.4 Universality..................................................................................................................................... 6

2.5 Aesthetics ........................................................................................................................................ 6

2.6 Human Factors ............................................................................................................................... 6

2.7 Operating environment.................................................................................................................. 6

2.8 Legal requirements ........................................................................................................................ 6

3 BACKGROUND INFORMATION: .................................................................7

3.1 FREQUENCIES............................................................................................................................. 7

3.2 MODULATION SCHEMES......................................................................................................... 7

3.3 DATA ENCODING SCHEMES ................................................................................................. 10 3.3.1 Manchester ................................................................................................................................ 10 3.3.2 Pulse Width Modulation............................................................................................................ 11 3.3.3 Code Hopping ........................................................................................................................... 11 3.3.4 Variable Pulse Width (KEELOQ) ............................................................................................. 12

4 HISTORY OF PAST TEAM .........................................................................15

4.1 Concept ......................................................................................................................................... 15 4.1.1 Antenna ..................................................................................................................................... 15 4.1.2 Receive and transmit ................................................................................................................. 16 4.1.3 Filter .......................................................................................................................................... 16 4.1.4 Signal processing....................................................................................................................... 16 4.1.4.1 Learn function....................................................................................................................... 16 4.1.4.2 Signal Detection/Recognition............................................................................................... 17 4.1.4.3 Retransmission...................................................................................................................... 17 4.1.5 USB........................................................................................................................................... 17

4.2 Recommendations they made...................................................................................................... 17 4.2.1 Improve power consumption..................................................................................................... 17 4.2.2 Range extension ........................................................................................................................ 18

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5 CONCEPT DEVELOPMENT:......................................................................18

5.1 Decoding and passing on signal for a selected car..................................................................... 19 5.1.1 Initial Concept (developed by last year’s team) ........................................................................ 19 5.1.2 Initial assumptions made by sponsor and our team ................................................................... 19 5.1.3 Initial Design upgrade for commercialization ........................................................................... 20 5.1.4 Research results (Screen capture of Sean’s key fob .................................................................. 20 5.1.5 Oversights in previous design ................................................................................................... 25 5.1.6 Peer review results..................................................................................................................... 25 5.1.7 End result of concept................................................................................................................. 26

5.2 Creating new key fob to activate user’s key fob ........................................................................ 26 5.2.1 Initial Concept ................................................................................................................................ 26 5.2.2 Concept Feasibility.................................................................................................................... 27 5.2.3 Sponsor reaction ........................................................................................................................ 27

5.3 Decoding and passing on signals in desired frequency ............................................................. 28 5.3.1 Initial Concept ................................................................................................................................ 28 5.3.2 Concept Feasibility.................................................................................................................... 28 5.3.3 House of quality ........................................................................................................................ 29 5.3.4 Comments made by last year’s team ......................................................................................... 29 5.3.5 Sponsor reaction ........................................................................................................................ 29

5.4 Morphological chart..................................................................................................................... 29

6 CHOSEN DESIGN FEASAIBILITY ASSESMENT:.....................................29

6.1 Antenna......................................................................................................................................... 29

6.2 Receiver......................................................................................................................................... 29

6.3 Transmitter................................................................................................................................... 30

6.4 Controller...................................................................................................................................... 30

6.5 Power............................................................................................................................................. 30

6.6 Legal Issues................................................................................................................................... 31

7 ANALYSIS AND DESIGN:..........................................................................32

7.1 Antenna......................................................................................................................................... 32

7.2 SAW Filter .................................................................................................................................... 32 7.2.1 315 MHz.................................................................................................................................... 32 7.2.2 433.92 MHz............................................................................................................................... 34

7.2 Receiver......................................................................................................................................... 35

7.3 Transmitter................................................................................................................................... 36

7.4 Controller...................................................................................................................................... 36

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7.5 Power............................................................................................................................................. 37

8 HOUSING DEVELOPMENT:.......................................................................39

8.1 Design Objective........................................................................................................................... 39

8.2 Concept Development .................................................................................................................. 39 8.2.1 Aesthetics........................................................................................................................................ 39 8.2.2 Function .......................................................................................................................................... 40 8.2.3 Materials & Manufacturing ............................................................................................................ 41

8.3 Concept Design & Feasibility ...................................................................................................... 41 8.3.1 Function .......................................................................................................................................... 41 8.3.2 Aesthetics........................................................................................................................................ 42

9 SENIOR DESIGN II PLAN: .........................................................................43

9.1 Board fabrication ......................................................................................................................... 43

9.2 Anticipated problems................................................................................................................... 43 9.2.1 Power......................................................................................................................................... 43

9.3 Prototype testing and modifications ........................................................................................... 43

9.4 Commercialization ....................................................................................................................... 44

10 APPENDIX:..............................................................................................45

10.1 House of quality............................................................................................................................ 45

10.2 Morphological chart..................................................................................................................... 46

10.3 FCC rules: Part 15 Section 209................................................................................................... 47

10.4 FCC rules: Part 15 Section 231................................................................................................... 48

10.5 Schematics..................................................................................................................................... 52 10.5.1 Maxim Receiver ................................................................................................................... 52 10.5.2 ChipCon Receiver................................................................................................................. 53 10.5.3 PIC Schematic ...................................................................................................................... 54 10.5.4 Saw Filter and Antenna Schematic ....................................................................................... 55 10.5.5 Transmitter Schematic .......................................................................................................... 55 10.5.6 Comparator Schematic.......................................................................................................... 56

10.6 BOM .............................................................................................................................................. 57

10.7 Flowchart Basic operation and flowchart software................................................................... 58 10.7.1 High Level Software Flowchart............................................................................................ 58 10.7.2 Detailed Software Flowchart ................................................................................................ 59

11 BIBLIOGRAPHY: ....................................................................................59

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1 Introduction In the past, remote keyless entry (RKE) systems were present only in higher end car manufacturers and models. As the technology becomes more economically feasible, more and more manufacturers are including these systems in a wider range of their cars. To make RKE systems available on many cars, manufacturers have to make them as cheap and long lasting as possible. This is why the range on many cars (from low to high end models) for remote keyless entry systems is very limited; usually less than 15 yards.

1.1 Desired functionality of RF repeater (Final product) The intent of this project is to create a commercially viable product to extend the range of the existing RKE system by designing a repeater that will receive the signal from a user’s key fob and retransmit the signal to the vehicle’s receiver. To do this, the repeater must be able to receive the signal from the key fob at a greater range than the vehicle’s built in receiver and then be able to quickly retransmit the same signal to the vehicle’s receiver. There are multiple reasons for extending the range of the RKE devices, but one of the main reasons emphasized by our sponsor is to be able to find your car in a parking lot without having to carry an extra device around. The lock or panic function on your key can be used to set off the audio alarm and headlights to find your car.

1.2 Our objectives The objective is to create a low cost stand alone system to improve the range of remote keyless entry systems in as many cars as possible. This project also needs to take into account the commercialization aspect which factors in cost for manufacturing in units of 10,000 and overall packaging of the device. The end product should also be visually appealing. To accomplish this project, our team consists of two electrical engineering students and two industrial design students.

1.3 Our Budget The sponsor has donated $200 for two senior design projects. We estimate that half of that will be assigned towards our project. Thus, we will have $100 available for prototype and testing. If more money is needed, we will have to contact the sponsor and make arrangements. Since this is a continuation of a senior design project from last year, we have some material available to use such as an ICD and programmer from Microchip to program a microcontroller (worth $900).

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2 NEEDS and REQUIREMENTS:

2.1 Range extension The repeater should extend the range of the key fob signal so that a signal generated from no less than 100ft is repeated. It is desired however, to have the range extended to 200ft under ideal conditions.

2.2 Power The battery life of the repeater must be 6 months. LEDs should be used to indicate the state of the battery.

2.3 Cost Since this is a commercialization project, the sponsor is aiming for a final selling cost of $25. The production cost per unit for batches of 10,000 units should be less than $15 and ideally $10 for materials.

2.4 Universality To make this a marketable product the more cars that it will work with, the more successful it will be. The sponsor has indicated that it is necessary to have this product work at both 315MHz and 433MHz. If it is necessary to have two separate products, one for each frequency, the sponsor has indicated that this would be acceptable if done to reduce the cost of the overall product.

2.5 Aesthetics Housing should complement the car interior landscape. The form should be small and unobtrusive but able to adapt to different functions such as solar panels, interchangeable color covers, or user interfaces. The driver’s needs such as visibility and control must be considered and accounted for in the final design.

2.6 Human Factors Any interaction the user may have with the final design must be considered and designed for. User interfaces should be intuitive and simple such as buttons, or battery doors. Installation and set up should also be as easy as possible involving the least number of steps and components. The user’s safety from any unwanted interaction should be design for in the final concept.

2.7 Operating environment The device should be able to withstand a varying temperature range (from -10 degrees Celsius to 50 degrees Celsius), such as that experienced inside a car.

2.8 Legal requirements Since this device involves wireless communication, the repeater should follow all rules and requirements set by the federal communications commission (FCC).

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3 BACKGROUND INFORMATION: Unlike wireless LAN communications standard 802.11b, there is no set standard (FCC or IEEE) for RF RKE systems. There are infinite ways to encrypt a signal, a couple of ways to modulate it, and a wide frequency range which it can operate in. The only constraint on these signals is the rules and requirements set by the FCC in CFR title 47 part 15.

3.1 FREQUENCIES The most commonly used modulation frequencies for RKE systems are 315MHz in the US and Japan, and 433.92MHz in Europe.1 Upon further research conducted by looking up FCC ID numbers from the back of key fobs on the FCC website (https://gullfoss2.fcc.gov/prod/oet/cf/eas/reports/GenericSearch.cfm), it was found that other frequencies that RKE systems operate on are 303MHz, 307.09MHz, 310MHz, and 868MHz (introduced in the summer of 2004). It was also found that manufacturers use different frequencies within their company for different model cars. For example, a 2004 Toyota Corolla operates at 315MHz, while a 2003 Toyota Tundra operates at 303MHz. It is unclear why this is the case but may be due to bandwidth crowding. Table 1 shows a list of car manufacturers and the frequencies at which their key fobs operate at. The information in this table was gathered by soliciting FCC ID#s located on the back of all key fobs and then using the FCC ID search page to find out the frequency of operation.

303 MHz 307.9 MHz 310 MHz 315 MHz 433.92 MHzToyota Hundai Suzuki Chrysler Honda

Dodge NissanFord Saturn

Mazda SubaruNissanSaturnSubaruSuzukiToyota

Volkswagon Table 1: Sample of RKE frequency spectrum use

Table 1 is not meant to be a summary of all RKE systems. It is just shown to illustrate the point that there is no set frequency standard for RKE devices (even within a single company).

3.2 MODULATION SCHEMES There are two modulation schemes that have been identified in use for RKE systems. They are amplitude shift keying (ASK) and frequency shift keying

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(FSK). ASK modulation modulates a carrier signal by multiplying it by a signal representing the binary data being modulated as shown below:

( ) ( ) ( )tftstu cm π2cos=

Equation 1: Modulated Message Signal

In general there may be more than 2 signals used to represent the data. For example 2 bits can be modulated with the 4 signals represented below.

( ) ( )( ) ( )( ) ( )( ) ( ) "11"sin4

"10"sin3"01"sin2

"00"sin

3

2

1

0

⇒=⇒=⇒=⇒=

ttsttstts

tts

Equation 2: Example of 2-Bit Message Signals

The form of ASK modulation used is a specific type called on-off keying (OOK). This means that instead of modulating two signals for binary “1” and binary “0” one signal is used, a constant, and the other is zero. This type of modulation is easiest to imagine by its simplest use of Morse code. A binary “1” is the carrier signal while a binary “0” is the absence of a signal as shown below:

( )tfuu

cπ2cos0

1

0

==

Equation 3: Example of ASK/OOK

Current RKE systems use OOK in an attempt to save power because the transmission of a “0” uses virtually no power. Below is an example of what OOK modulation may look like. As may be noticed, the signal may be indistinguishable from noise as long as the message signal (“0” or “1”) is held at “0”. For demodulation purposes this will cause problems because the carrier signal may be lost, and the receiver may not be able to determine if there any signal at all. One solution to this problem is to use an encoding scheme like Manchester encoding, explained in Section 3.3.1. This modulation scheme ensures that half of the signal must be “1”.

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Figure 1: Sample ASK modulated signal

FSK modulation changes the frequency of the carrier signal by some ∆fc, a small fraction of fc. Like in ASK, multiple bits can be sent in one signal. The equations for 2-bit and multiple bit FSK modulation are shown below.

( ) ( ) 1,...,1,0,22cos2

−=∆+Ε

= MmftmtfT

tu cs

m ππ

Equation 4: Multiple bit FSK modulation

An example of FSK modulation is shown in the figure below. This example is an exaggerated modulated signal because the change in frequency, ∆fc is on the same order as fc. The change in frequency is so large in order to illustrate how the frequency changes for message signals of “1” and “0”. If a real signal were done in the same way the bandwidth needed would be too large.

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Figure 2: Sample FSK modulated signal

3.3 DATA ENCODING SCHEMES After researching information, it was found that there are three types of encoding used with RKE systems. Manchester encoding and Variable pulse width encoding are the most widely used types.

3.3.1 Manchester Manchester encoding is a form of data communication where each bit of data has at least one transition. It is therefore considered to be self-clocking since the clock signal can be embedded into the signal. Each bit is transmitted over a predefined period and there will never be long periods of time without a clock transition. This prevents loss of clock synchronization and bit errors from signal drifting. There are two opposing conventions for representing Manchester encoded data.2 The first convention published specifies that with a low to high transition (low level for first half of bit period and high level for second half) a 0 is represented. For a high to low transition, a 1 is represented. The second convention (IEEE standard 802.4) states that a 0 is represented by a high to low sequence and a 1 is

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represented by a low to high sequence. A sample Manchester encoded signal is shown in Figure 3.

Figure 3: Encoding of 11011000100 in Manchester code

3.3.2 Pulse Width Modulation Pulse width modulation is where the width of pulses (duty cycle) are controlled to pass information over a channel. Different pulse width values correspond to specific data values. The pulses are sent at regular intervals, but the length of each pulse varies. An example is shown in Figure 4.

Figure 4: Example of pulse width modulation

3.3.3 Code Hopping Years ago, car thieves in Europe turned to technology to help them steal cars.3 They created and used devices called “code grabbers” which captured and recorded the coded signals that arm and disarm a car when a user presses the buttons on their key fob. They later played back the signal to illegally disarm the alarm system, easily stealing the car. This is why car manufacturers now use the code hopping system which can be made from both hardware and software to encrypt signals before being transmitted to the car. This encryption is done by randomly changing the code that transmits each time you arm or disarm the car alarm. There are numerous methods to accomplish this, but one way is by using a complex algorithm so that the same code never repeats. Both the transmitter on the key fob and the receiver in your car has to use code hopping in order for the system to work.

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3.3.4 Variable Pulse Width (KEELOQ) In response to the need of code hopping technology, Microchip has come up with its own line of code hopping devices under the name brand KEELOQ. KEELOQ is proprietary technology based on random bits generated by a non-linear encryption algorithm (using a 64-bit encryption key) that creates a unique transmission on every use. In RKE systems, the low end fixed encoders are used. The encoders generate a signal for the transmitter with 32 random bits, 28/32 bits serial number, and information bits used to tell the car what function to perform. The total transmission can be up to 69 bits long. The operation of a KEELOQ encoder is shown in Figure 5. A summary of the transmission bits for different KEELOQ encoder models is shown in Figure 7. When KEELOQ encoders are used on the transmitter side of a RKE device, a KEELOQ decoder needs to be used on the receiving end. The operation of a KEELOQ decoder is shown in Figure 6. This can be done with hardware (Microchip part numbers HCS5XX) or software. The software decoders come as part of a licensing package and needs to be purchased. The price of this package is not advertised but is expected to be very costly.

Figure 5: Operation of KEELOQ encoder4

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Figure 6: Operation of KEELOQ decoder

Figure 7: KEELOQ encoder transmission summary5

Each RKE transmission follows a specific format created by the manufacturer. Using the KEELOQ encoding scheme also integrates a code hopping transmission format into the transmitted signal. This makes it easier when decoding the signal

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since the exact number of bits for a specific function is known (from Figure 7) and the sequence of data transmission is known (Figure 8).

Figure 8: KEELOQ transmission format

Figure 9: Graphical representation of the transmission format

As with regular pulse width modulation, the variable pulse width modulation used by the KEELOQ encoder varies the duty cycle of the pulses to signify if a bit is 0 or 1. For a 0, the beginning part of the signal is kept high for 2Te and then pulled low for Te. For a 1, the beginning part of the signal is kept high for Te and then

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pulled low for 2Te. This can be seen in Figure 10. Te is the length of time for a basic pulse element (shortest pulse length used).

Figure 10: Variable pulse width modulation bit format

Since using this Microchip technology cuts development time that would otherwise be spent on creating a secure encryption algorithm, many companies choose to use Microchip encoders and decoders in their devices.

4 History of past team This RF repeater commercialization project is a continuation of a project that was started last year. The previous team came up with three initial concepts: receive and retransmit at the same time, receive, demodulate, store, modulate and retransmit the signal, and frequency shift to lower frequency, sample with A/D converter, store, frequency shift back up, and transmit. The concept that they decided to implement was the demodulation scheme. The simultaneous receive and transmit scheme was ruled out since the two signals would interfere with each other since they are transmitted through the same medium. The other scheme was eliminated due to the amount of memory and processing power needed to implement.

4.1 Concept A Microchip receiver demo board and an Agilent Oscilloscope were used to initially capture the signals coming out of a 2004 Toyota Corolla and a SABB (sponsor’s car). After capturing several signals from the SABB car and analyzing the data, it was concluded that the signal were Manchester encoded and encrypted since after every press of the key fob, the whole signal changed. They then analyzed the data obtained for the Toyota Corolla. After using MATLAB to decode the data, they opened the key fob and found a HCS361 Microchip encoder inside. Looking up the part number, they were able to find the datasheet for the encoder and know that the signal was variable pulse width encoded and that the transmission format is as shown in the figures in section 3.

4.1.1 Antenna The final design used a quarter wave miniaturized, omni-directional antenna from Tricome The TCA12B antenna is an advanced, surface mount integrated antenna designed for 315MHz with a bandwidth of 10MHz and a gain of typically -3dBi.

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The impedance of the antenna was 36 ohms. In order to match this with the impedance of the PCB trace (to minimize power loss), an LC matching circuit was used.

4.1.2 Receive and transmit The final design for the receiver was to use an rfRXD0420 receiver IC. This is the same receiver chip used on their prototype board which was a receiver demo board obtained from Microchip. This receiver chip includes a low noise amplifier, bias circuitry, mixer, an intermediate frequency amplifier, and received signal strength indicator. The final design for the transmitter was switched from using Maxim MAX1472 to Microchip’s rfPIC12F675. This was done to reduce the cost of the overall product by $1.50 and for easier integration (using all Microchip parts). The new transmitter includes a PIC microcontroller built in. However, this part of the device was bypassed and not used.

4.1.3 Filter A SAW filter was used as the pre-select filter between the antenna and receiver. The bandwidth of the filter was 600 kHz with a center frequency of 315MHz. This filtered out most of the noise received by the antenna before reaching the receiver. A SAW filter was chosen over active and passive filters because it does not require any power and has a very narrow pass band. The only disadvantage is that it is expensive.

4.1.4 Signal processing Since the same antenna was used to receive and transmit the signal, a PIC microcontroller was used to control the receiver and transmitter so only one was active at any given time. The PIC was also used to decode the signal received from the receiver and pass on the complete signal to the transmitter at the end of the receive cycle. The code written for the microcontroller was based around the 2004 Toyota Corolla. Thus, the repeater only works for cars using the HCS361 Microchip encoder.

4.1.4.1 Learn function A learn function was implemented in the microcontroller so the repeater could learn the serial number of the user’s key fob in order to only repeat that signal. The user would press a button on the repeater and then a button on the key fob. From the transmission format obtained from the datasheet for a HCS361 encoder the repeater knew exactly where in the signal to look for the serial number. The serial number of the key fob, was then stored for future reference. This was done only for the Toyota Corolla. Since the signal for the SAAB was encrypted, and no data was available to find out how to decrypt it or what the transmission format of the data was, it could not be decoded. Thus, the learn function created only works for key fobs that use the HCS361 encoder by Microchip.

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4.1.4.2 Signal Detection/Recognition Using information gathered from the Microchip datasheet for the encoder in the key fob, the team knew that there was a 50% duty cycle preamble and a sync header before any key fob specific data. Since this part remained constant, knowing this, the repeater functioned by taking the data received from the receiver and compared it to the known preamble and sync data (obtained from the datasheet). If this information was correct, the repeater started to record the received data. After recording the signal, the microcontroller would look into the signal to find the serial number and compare this number to the serial number obtained from the learn function. If they were the same, the microcontroller turned the receiver off and the transmitter on to transmit the stored data. If the serial numbers did not match, the data was discarded and the microcontroller waited for new information from the receiver.

4.1.4.3 Retransmission Since it was known that all signals from a HCS361 encoded key fob has a 50% duty cycle preamble and a sync header, this information was not stored on every receive cycle. It was kept in program memory. The sync portion of the signal is 16 of 67 bits in the signal. Not storing this information in RAM significantly decreases the amount of RAM needed to store any receive signal. Upon retransmission of a valid receive signal, the known preamble and sync header were transmitted followed by the stored receive signal.

4.1.5 USB

To implement their design concept for multiple models the previous team suggested using USB to interface the repeater with a PC. The user could then go to a webpage and type in their car information to download code that told the repeater how to function for that specific model. Using this and the learn function, the repeater would only store and retransmit the user’s specific key signal.

4.2 Recommendations they made

4.2.1 Improve power consumption The final board design for the repeater drew an average of 10mA. An average alkaline battery has a current rating of 2500mAH. This would mean that their design would only last for 250 hours or 10.4 days. This is unacceptable. The recommendation made was to put the receiver in standby mode most of the time and periodically wake up to check for a signal. Another recommendation made

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was to change the receiver design. The Microchip rfRXD0420 uses 8.2mA when on and only 100nA when in standby mode. This could significantly reduce the power consumption.

4.2.2 Range extension Using the Microchip receiver demo board, a range of 150ft was obtained for the repeater. However, when the team used their receiver design for the repeater, no range extension was achieved. The cause that they reported was bad board construction due to the outline of the antenna.

5 CONCEPT DEVELOPMENT:

Figure 11: Pugh's Feasibility Method

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Figure 12: Weighted feasibility chart

5.1 Decoding and passing on signal for a selected car

5.1.1 Initial Concept (developed by last year’s team) The repeater designed last year worked for a 2004 Toyota Corolla at 315MHz with ASK modulated signals. It included a learn function that would be able to store the serial number of a user’s key fob and only retransmit signals from that key fob. It was successful at retransmitting the user’s specific key fob signal but not at increasing the range of the signal.

5.1.2 Initial assumptions made by sponsor and our team At the beginning of this quarter, the sponsor made some assumptions stated below.

1) The background information for building the repeater was already done. Commercialization of the repeater was feasible.

2) The transmitter and antenna circuitry were operational. All that needed to be done was redesigning the receiver for better range and power consumption.

3) Characterizing all key fob signals could easily be done. 4) The scope of our project was to take their design, improve upon it

by fixing the receiver, finalizing the PCB, creating a USB interface, and fabricating housing for the device.

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5.1.3 Initial Design upgrade for commercialization Hardware: The receiver used last year consumed a lot of power when not in standby mode. To solve this problem, instead of using just one receiver chip with a low noise amplifier, power amplifier, and demodulator in one, three separate components can be used. A redesign of the receiver should also fix the range problem. The antenna and transmitter design will be kept since these parts worked last year and will save design time.

Software: To make a truly universal repeater, all key fob signals need to be classified and put into a database. This classification should include data such as frequency of operation, modulation scheme, encoding scheme, and transmission format. Using this information, microcontroller code can be created for each of the different schemes to allow the repeater to work with different model cars. After the code is written for all models, it can be incorporated into a website. The user will go to the website, select their car from a list and download the microcontroller code to the repeater through a USB connection.

A boot loader program needs to be written to allow the microcontroller to interface with the PC through a USB connection. This program will also allow the PC to erase the program memory of the microcontroller and download the new code from the website. On the PC side, a driver for the repeater devices needs to be created and an executable function to download code to the microcontroller needs to be created.

5.1.4 Research results (Screen capture of Sean’s key fob Using the Microchip receiver demo board and an oscilloscope the key fob signals for a 2005 Honda Civic were captured and analyzed. The key fob lock and panic buttons were pressed ten times each. The unlock function was pressed only two times since the intention was to not pass on the unlock function. So all that was needed was to figure out where in the signal the button information was stored. Figure 13 is the data captured from one of the lock signals. Comparing 10 different lock signals that were captured, it was found that there is a high signal for approximately 2ms followed by a sync preamble of approximately 163 cycles. Although, there were some signals that had preambles of 165 cycles. Following the preamble was a signal that remained constant between the lock, unlock, and panic functions. This could be the serial number of the car. But from Figure 13 it can be seen that there is also another part of the code that remains constant. Without any information about the transmission format, or software code, it is impossible to tell for sure what the bits in the signal represent.

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Figure 13: Lock signal for 2005 Honda Civic

Between the two constant parts of the signal there is a portion that remains the same within the same type of signal, but varies between different functions (remains constant throughout all lock signals but varies between a lock and panic signal). This part is probably where the information about which button was pressed is stored. After comparing 10 lock signals, 10 panic signals, and 2 unlock signals, it was found that the last part of the signal is totally random. This is probably the code hopping portion. But since there is no documentation available it is impossible to be positively sure.

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Figure 14: Unlock signal for 2005 Honda Civic

As stated previously, the key fob used last year had a Microchip encoder in it. To try and find out what other car manufacturers use the Microchip KEELOQ encoder in their key fobs, a letter was written to a public relations representative at Microchip. Due to customer privacy rights, they were unable to disclose their clients. However, they informed us that on the back of every key fob is an FCC ID #. This number can be used to search the FCC website to find any information that was filed by the company.

The FCC ID# on the back of the 2005 Honda Civic was NHVWB1U523. This number was searched on the FCC website and no information was found. This may be due to the fact that the key fob is too new. Searching

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Figure 15: Panic signal for 2005 Honda Civic

the FCC website with NHVWB1U521 however, brings up a device that looks similar to the 2005 Honda Civic key fob. The device however, was submitted in 1999 which means it is probably an older version of the key fob. The block diagram for the key fob obtained from the website is shown in Figure 16. The key fob uses a microcontroller rather than the KEELOQ encoder. From this information, and by looking at the signals generated from the key fob, it was concluded that the 2005 Honda Civic uses Manchester encoding. The schematic for the key fob transmitter is shown in figure 17.

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Figure 16: Block diagram for 2005 Honda Civic

Figure 17: Schematic for 2005 Honda Civic Transmitter

Since a microcontroller was used in the key fob, and not a Microchip encoder, the transmission format is not known. Initially, the sponsor wanted the repeater to work for only the lock and panic functions. We do not want the user to accidentally unlock their car. But in order to do this, you would have to know the transmission format of the signal in order to know where in the signal to find the serial number (for learn function) and whether or not the signal was a lock, unlock, or panic. A lot of work was done to characterize just this one car signal since it did not have a datasheet of how the key fob data transmission was accomplished.

After finding FCC ID #s for other cars (Toyota Camery, Dodge Durango, Ford Explorer), it was found that some manufacturers used the KEELOQ encoder while others used microcontrollers (usually 4 bits). This makes it difficult to

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model all cars to date since key fobs using a microcontroller do not advertiser their specific transmission format like the KEELOQ encoder. Having a database that holds the classification of all key fob signals is also not feasible since someone will have to keep the database updated every year with new car models that come out. This will cost a lot of money. A short list of car models and their classification are shown in Figure 18.

Manufactuer FCC ID # Frequency Encoding

Hundai OSLOKA-221T 307.9 MHz microcontrollerDodge GQ43VT17T 315 MHz HCS361 (KEELOQ)

Volkswagon NBG 8137 315 MHz microcontrollerHonda NHVWB1U521 433.92 MHz microcontroller

Genral Motors KOBLEAR1XT 315 MHz HCS361 (KEELOQ)Kia PLN BONTEC-T009 315 MHz HCS300(KEELOQ)

Nissan NHV BU427 315 MHz microcontroller Figure 18: Classification of key fobs

5.1.5 Oversights in previous design 5.1.5.1 Learn Function

The learn function only works if you know where in the signal to find the serial number of the car. This is not easy as demonstrated by the team (could not decode signal for SAAB). The task is almost impossible since companies are not willing to give up their encryption or encoding schemes (this counter acts the purpose of having any encoding or encryption)

5.1.5.2 Universality

The previous design was based off of one car using the HCS361 Microchip encoder. It would not work for any cars not using this encoder. Just as for the learn function, it is impossible to find out information about the key fobs from the manufacturers since they are not willing to give out this information. Also, may designs that we came across when classifying key fobs used microcontrollers. This significantly increases the work needed to decode a signal since there are infinite ways the microcontroller can be used to encode or encrypt a signal.

5.1.6 Peer review results A peer review was held during week 6 of this quarter. The purpose of the peer review was to get feedback from other engineering students and fix possible design flaws. After going over the information we recovered during the previous weeks, the feasibility of our design was questioned. During the feasibility portion of the review, our requirements were considered impossible to do with the current design. As stated before, there are infinite ways to encrypt a signal, a couple of ways to modulate it, and a wide frequency range which it can operate in. All key fob manufacturers are required to file their device with the FCC and this information is sometimes available to the public by searching through the FCC website with a known FCC ID. The frequency range of a specific key fob and the

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modulation scheme can be recovered using the FCC ID of the key fob. The main design obstacle is the encryption portion of the signal since information about this is proprietary to the manufacturer and not readily available.

5.1.7 End result of concept The reason why this concept was initially chosen was because it was assumed that the concept was proved by the previous team. It was assumed that all that needed to be done was upgrade the design. However, after spending a lot of time analyzing the concept, it was proven to not be feasible. Thus, the following concepts were researched.

5.2 Creating new key fob to activate user’s key fob

5.2.1 Initial Concept Due to the feasibility of being able to complete the project using the previous concept, the next concept that was examined was to create a brand new key fob system utilizing the old system. In this design, a separate key fob would be given to the user sending a brand new signal to the repeater box positioned in the car. The original key fob would be located inside the repeater box. When the repeater receives the new RKE signals it would mechanically operate the original car key fob, sending the original manufacturers RKE signal to the car’s receiver.

Figure 19: New key fob system level 1 diagram

Figure 20: New key fob system level 2 diagram

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5.2.2 Concept Feasibility There are many feasibility issues with this concept. The obvious challenge is making a mechanical device to actuate the key fobs universal. This is a problem since key fobs have different button placements and designs. Using motors and actuators also consume a large amount of power which will significantly lower the battery life. Motors will also significantly increase the size of the device and cost.

Modern key fobs are also often integrated with the ignition key. This would cause a car security risks if the car was broken into and the user’s key was in the device.

There are advantages to this design. By creating a new key fob system, the device will be able to select which signal to activate (such as only lock and panic). This can be done by measuring the signal strength on the receive size to measure how far away the user is. If the user is close, the unlock function can be activated, else it will be disabled.

Since there are encoding technologies available to create key fobs (such as the Microchip KEELOQ encoder) it will be a fairly easy task to implement a new key fob design. The hard part will be designing the mechatronic system and its controller. This may cause the device to cost significantly more than the estimated $10-$15.

This design will also not need a USB interface. This will remove the extra time needed to research PC drivers and USB enumeration steps. It also does not depend on the transmission format, modulation scheme, frequency, or encoding technique of the user’s key fob.

5.2.3 Sponsor reaction Our sponsor chose the next concept over this one. Due to the cost and complexity of design

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5.3 Decoding and passing on signals in desired frequency

Figure 21: Block diagram of chosen design

5.3.1 Initial Concept This design concept does not decode the incoming signal to find out the serial number of the user’s key fob. It is just a generic repeater that captures all key fob signals in the frequency range, stores it, and retransmits.

To make the repeater universal, the PCB board will be split up into modules. Since the receiver and transmitter are frequency dependent, different crystals will have to be used. Having the PCB modular allows the user to just change boards for the antenna, receiver, and transmitter, keeping most of the hardware the same. This is very useful in a marketing standpoint since then a user will only have to buy different antenna/ receiver/ transmitter modules to switch between two different cars, rather than buying a completely new repeater. This idea will also be very helpful if this design goes into production. If one PCB will be used instead of having it modular, multiple antenna/ receiver/ transmitter sections will have to be on the board with a switch that can change between them to select the frequency of operation. This will increase the cost per board and the overall cost per repeater.

5.3.2 Concept Feasibility This concept is the most feasible out of the three presented here. The general materials needed are less than that used for the previous team’s design. There is no need for the USB to PC interface or the learn function. This will allow us to use a microcontroller that does not have a built in USB function. However, the new microcontroller will need to have significantly more RAM.

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As stated before, having the PCB modular will allow the repeater to be manufactured and sold at a cheaper price.

Unlike the previous two designs, this concept is not model specific. It is truly universal since any key fob that operates within the specified frequency will work.

5.3.3 House of quality See Appendix 11.1

5.3.4 Comments made by last year’s team The previous team was weary about pursuing a concept like this due to possible FCC regulations. We proposed our design concept to the FCC and received approval the last week of senior design I.

5.3.5 Sponsor reaction The sponsor initially liked the first concept when he thought that it would be easy to implement since all that needed to be done was use the design from the previous year and upgrade it. After researching what needed to be done, and realizing the feasibility issues, we had to choose a different concept to implement. This concept was more acceptable to the sponsor than the previous concept where there was a redesign of the key fob system with mechanical actuators.

5.4 Morphological chart See Appendix 11.2

6 CHOSEN DESIGN FEASAIBILITY ASSESMENT:

6.1 Antenna The chosen design will use the same antenna as last year for the 315 MHz repeater since the frequency of transmission is the same. This will cut the research time needed to find an alternative antenna. Since a 433.92MHz repeater will also be built, an antenna for this frequency will need to be found. This will be relatively simple since the manufacturer that makes the 315MHz antenna also makes one that operates at 433.92MHz.

6.2 Receiver The previous team switched from using a Maxim receiver chip to a Microchip receiver. Their reasons were to reduce the cost of the overall system, and for better integration, since all other chips were Microchip parts. One suggestion made by the previous team was to look into using a different receiver chip. The reason for this was to reduce the overall power consumption.

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The receiver, when in the on position, used more than 80% of the total power consumption. Using a different receiver may solve two problems: power consumption and increased range.

6.3 Transmitter Since the repeater only needs to retransmit a short distance (less than 10ft) the range of the transmitter does not need to be improved at all. Thus, the same transmitter chip will be used as on the previous design. However, while researching different receiver components, a chip was found that had both a transmitter and receiver on it. This chip will also be integrated into the PCB to try to see if one chip can be used for both the receiver and transmitter.

6.4 Controller With the chosen design concept, a microcontroller will be used for control circuitry and signal processing. Since the repeater will receive, store, and retransmit the signals, the microcontroller will have to have enough memory to store a complete key fob signal. Since only one signal will be received and transmitted at a time, only enough memory to store one signal will be needed. A DSP could be used instead of a microcontroller if the signal of the key fob before demodulation were to be sampled. But this method is power intensive and not feasible since the chosen receiver has a built in demodulator. Since the new repeater will not have a USB interface, the microcontroller will no longer need USB functionality.

6.5 Power By searching the internet, it was found that the highest ampacity-hour battery was a 2500mAH NiMH rechargeable battery. In order to have the repeater device last for 6 months (4320 hours) using this battery, the repeater could only draw an average of 0.58mA or 580 uA per hour. This is not feasible at all!

A more feasible alternative would be 3 months (2160 hours). This would mean that the repeater could only draw an average current of 1.16mA per hour. This may be feasible. But measurements will have to be taken when the prototype device is built to measure actual power consumption.

For the transmitter, battery life of 3-5 years is desirable. Battery life is also important for the receiver, as the receiver must always be on, listening for the user's transmission. Typical specs call for no more than 1mA of average current. One way system designers solve this problem is by leaving the receiver on for brief periods of time, long enough to determine if there's a valid transmission. The

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receiver "sleeps" the rest of the time. The receiver must be able to wake-up very fast, to maximize the energy saved.6

An alternative to using just batteries is to use either solar cells to recharge the battery, or the car adapter. Solar cells are very brittle and costly. To increase the durability of solar cells, companies sell encapsulated (enclosed solar panels) high output solar cells. These allow for normal handling without breakage and cell damage. Table 2 shows the cost of different solar cells from nexttag.com. The cost of the solar cells are very high. At this point in time, it is not feasible to use solar cells since the cost of a cell is almost as much as the estimated total cost of the repeater.

Voltage Current Dimensions Cost1.5 V 50 mA 1.75" x 1" x 0.25" 8.951.5 V 100 mA 3" x 1.75" 11.951.5 V 200 mA 3.75" x 2" x 0.25" 19.953 V 20 mA 1.75" x 1" x 0.25" 9.953V 100 mA 3.75" x 2" x 0.25" 19.95

Table 2: Solar cell costs7

Using a car adapter is also not feasible. To utilize this concept, a battery charging circuit will have to be integrated on to the board. In addition, voltage regulators will have to be used since the car adapter outputs 12V and the circuitry in the repeater uses 2.0V-3.3V.

6.6 Legal Issues The whole design concept is based on the assumption that our idea follows the FCC rules and regulations. CFR title 47 Part 15 section 231 pertains to frequencies in the 40.66-40.70 MHz and above 70MHz. It is also for periodic operation in this band. Since our repeater only receives, stores, and retransmits the signal once per press of the key fob, there is no periodic retransmission of the same signal. Based on this information, it was assumed that CFR title 47 Part 15 section 231 does not apply to our situation. Our design is also subject to CFR title 47 part 15 section 209. This rule states the maximum field voltage that the repeater can transmit over a specified distance. We have been in contact with the FCC for the past three weeks and were notified earlier this week that our design meets FCC rule and regulations.

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7 ANALYSIS AND DESIGN:

7.1 Antenna Since the antenna chosen by the previous team worked properly, it will be reused. The antenna chosen last year was a 315MHz antenna made by Tricome. The part number is TCA12BR-315. Soyter components is a distributor for Poland and Russia. The distributor for the US does not have good contact information so parts will be purchased from Soyter. The € to dollar conversion is shown below. The cost per antenna is approximately $1.89.

1 € = 1.1807 U.S. dollars

TCA07FRE-433 433MHZ Tricome antenna 1.6€ $1.89TCA12BR-315 315MHZ Tricome antenna 1.6€ $1.89

Table 3: Antenna cost8

Analysis from the previous team shows that the impedance of the antenna is 36 ohms for the 315MHz antenna. Since the traces on the PCB are 50 ohms, the antenna will have to be impedance matched using inductors and capacitors.

7.2 SAW Filter

7.2.1 315 MHz A pre-select filter is needed to filter out unwanted frequencies captured by the antenna. A SAW filter has to be selected to accomplish this. The SAW filter selected is a surface mount device with part number AFS315E manufactured by ABRACON. The characteristics for this device are shown in Table 4. The impedance matching circuit needed to match the circuit to the 50 ohm traces on the PCB is shown in Figure 22. The pin out connection for the filter is shown in Figure 23. This filter was chosen because it was used in the previous team’s design. All the receiver datasheets also suggest using SAW filters.

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Table 4: 315 MHz SAW Filter Characteristics

Figure 22: Impedance Matching Circuit for 315MHz Saw Filter

Table 5: Pin connection for 315 MHz SAW Filter

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7.2.2 433.92 MHz For the 433.92 MHz receiver, the ideal SAW filter is a surface mount device with part number AFS433E-01 manufactured by ABRACON. This device has a bandwidth of only 600kHz and a center frequency of 433.92MHz. The characteristics of this filter are shown in Table 6.

Table 6: 433.92MHz SAW Filter Characteristics

However, after looking at different distributors we were unable to find this part in stock. Companies listed them in their catalog, but required a minimum order of 1,000+. If the repeater design goes into production, this may be feasible, but not for prototyping.

An alternative SAW filter was chosen. The part number is AFS434S3 by ABRACON. This device has a bandwidth of 4MHz, but is available for purchase. The characteristics of this filter are shown in Table 7.

Table 7: 434MHz SAW Filter Characteristics

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The pin outs for this filter are shown in Table 8. From the datasheet, it was found that no impedance matching is required for this circuit to a 50 ohm PCB.

Table 8: 434MHz SAW Filter pin out

7.2 Receiver In the receiver circuitry there is a need to maximize the sensitivity and minimize the amount of power. The greater the sensitivity of the receiver, the farther possible range that may be obtained by the repeater. It may be possible that a receiver with a very good sensitivity will not perform any better than one with worse sensitivity. This is because the SNR may become the limiting factor which will come from the transmitted signal power, but we are unable to change SNR with the receiver part. Power in the previous design was much higher than is possible to achieve a 6 month battery life. To lengthen the battery life, power is one of the key parameters of the receiver that we are looking for. Multiple frequencies and modulation schemes are also essential for achieving universality of the repeater. Some of the receivers considered for this design are listen in the table below. All of these devices have multiple modulations and frequencies. Manufacturer Maxim Microchip Chipcon AtmelPart Number MAX1471 rfRXD0420 CC1100 TA5423Reciever Sensitivity -108 dBm -104 dBm -110 dBm -106 dBmCurrent drawn 7mA 8.2 mA 15.6mA 10.5mAModulation ASK/FSK ASK/FSK ASK/FSK ASK/FSKFrequencies (MHz) 315/433 300-450 315/433/868 315/345/433.92/

868.3/915Cost per unit $5.86 $4.08 $2.49 N/ACost per unit (Qty of 10000+) $2.85 $2.79 $1.92 N/A

Notes TransceiverFigure 23: Comparison of receivers

Based on the table above, the board is being implemented with both a Maxim chip and a Chipcon chip. The final board will only have one receiver on it. The Chipcon chip is a transceiver and may be able to replace both the transmitter and receiver as well as many external components used. This would possibly lower the cost of the board, size of the board (giving more options for the housing) and also may lower the power consumption, improving battery life.

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The Microchip part was ruled out because of the documentation available online. It may be a superior part but it is not possible to tell or take full advantage unless the designers are aware of how to use it. The Maxim and Chipcon chips both document the polling function. The polling function turns the receiver into standby and checks for a signal at some duty cycle set by registers or external components.

7.3 Transmitter The transmitter circuitry from the previous design is working to spec. Because of this we are continuing to use the same transmitter and circuitry with a few minor changes to interconnect to the newly designed circuits. One of the changes made is we are connecting the transmitter to the Antenna as well as an option to connect it to the loop antenna (trace on the PCB) used in the previous design. The Chipcon part is a transceiver and may be able to take over all functions of the current transmitter. The schematic has the option of by-passing the current transmitter to allow the Chipcon transceiver the ability to transmit. If it is possible to use the Chipcon part the cost would decrease by at least $2.25, the cost of the transmitter, as well as any external circuitry required. The Chipcon part will also conserve board space giving more options in housing.

7.4 Controller

Since the microcontroller will be used to sample and store the received information from the receiver, the sampling rate needs to be obtained. To avoid losing information in the signal, it will need to be sampled at a higher rate than the frequency of the signal. In general, to preserve the full information in the signal, it is necessary to sample at least twice the maximum frequency of the signal. This is known as the Nyquist rate. According to the sampling theorem, a signal can be exactly reproduced if it is sampled at a frequency F, where F is greater than twice the maximum frequency in the signal.

From the captured data results received for the 2005 Honda Civic signals, the longest transmission length was around 280mS. From the previous year, the transmission length for the 2004 Toyota Corolla was about 11mS and the transmission length for a SAAB was about 12mS.

Taking into account this data, it will be assumed that 400mS will be the longest transmission time length encountered. The next step is to find the sampling frequency.

Since we would like to get the stored signal as close to the received signal as possible, a sampling of 10 times per Te will be attempted. Te is the smallest bit

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time for a specified signal. For the 2004 Toyota Corolla, Te was 260uS. For the 2005 Honda Civic, Te was 500uS. Taking this into account, Te will assume to be 150uS. The amount of RAM needed for different sampling frequencies are shown in equations 6 thru 8.

KHzuS

samplesKHzuS

samplesKHzuS

samples 3.53150

860150

97.66150

10===

Equation 5: Calculation of Sampling Frequencies

bytesbitsuS

samplesmS 3333667,26150

10*400 ==

Equation 6: RAM needed for 66.7KHz sampling frequency

bytesuS

samplesmS 3000150

9*400 =

Equation 7: RAM needed for 60KHz sampling frequency

bytesuS

samplesmS 2667150

8*400 =

Equation 8: RAM needed for 53.3KHz sampling frequency

The specifications for different microcontrollers are shown in Table 9. Only Microchip microcontrollers are being selected because a programmer is already available which will save $900. The most important factor in choosing a microcontroller in this application is the amount of RAM available. Ideally, a sampling frequency of 66.7 KHz would like to be achieved. Based on this information and cost (as seen in Table 9), the PIC18F2525 microcontroller was selected.

Manufacturer Part No RAM I/O Pins Voltage Data EEPROM Cost ( >100+)

Microchip PIC18F2525 3968 bytes 25 2-5.5V 1024 bytes 5.59Microchip PIC18F6527 3936 bytes 54 2-5.5V 1024 bytes 5.81Microchip PICF2620 3968 bytes 25 2-5.5V 1024 bytes 6.13

Table 9: Microcontroller comparison chart

7.5 Power The life of a battery is given in terms of current hours. When batteries are connected in series, their voltages add together and their current characteristics stay the same. The reverse is true for batteries that are connected in parallel. To increase the milliamp hour rating of batteries, instead of using 3 batteries in series, we can use 3

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batteries in series in parallel with 3 batteries in series. This would effectively double the current rating. From our research, it was found that rechargeable batteries have lower ampacity values than one time use batteries (usually only 2500mAH). So although they maybe cheaper to use in the long run, they do not last as long. Since power is a major issue in this project, we will recommend that users use one time use alkaline batteries. These batteries are easily obtained and fairly inexpensive. Another option may be to use bigger size batteries (such as a C size instead of AA). From Table 9 it can be seen that the capacity of AA batteries are 2850mAH while the capacity of C batteries are 7800mAH. The ampacity of Engergizer AA batteries are also 2850mAH while the ampacity of C batteries are 8350mAH. From this analysis, it seems the best way to resolve the power issue is to lower power consumption or increase the size of the battery being used.

Table 10: Summary of DURACELL alkaline battery properties9

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Table 11: Summary of Energizer alkaline battery properties10

From Table 12, Energizer batteries are the best option to use when considering ampacity and initial startup costs.

Brand Size Type Capacity Cost perPowerEx AA NiMH 2500mAH $3.24Duracell AA Alkaline 2850mAH $1.30Energizer AA Alkaline 2850mAH $0.69

Table 12: Cost comparison of batteries11

8 HOUSING DEVELOPMENT:

8.1 Design Objective The housing design objective is to develop product housing for an RF Repeater which will be universally aesthetically pleasing to consumers and their automobiles. Human interaction with the device should be intuitive and simple. Mounting and placement should be non-obtrusive and simple for users to do themselves. Materials and manufacturing must meet the target pricing of $10-$15.

8.2 Concept Development

8.2.1 Aesthetics To make the housing universally pleasing in car interiors we observed a variety of car interior and exterior styling. We also drew from successful car accessory

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products for ideas of form. Our goal was to have the research inspire concept ideas that would be unobtrusive to existing car interiors.

Figure 24: Different forms for car accessories

8.2.2 Function The conditions of a car interior make it important for the housing to have a secure foundation. It should also be easy enough so the user can install it themselves. We researched mounting locations as well as mounting products to come up with our design solutions.

Figure 25: Possible mounting locations for the repeater

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Figure 26: Different methods for attaching the repeater to the car

8.2.3 Materials & Manufacturing ABS plastic or a high grade polystyrene is recommended as the best material for the housing construction. ABS will provide the best resistance to the temperature changes and UV exposure as well as being cheap to manufacture as opposed to other materials such as polypropylene, or polyethylene.

After looking at injection molding, rotational molding, vacuum forming, and pressure forming it cannot yet be determined exactly which process to use. The best two options would be pressure forming or injection molding. The decision to use one or the other will depend of the final dimensions of the housing, mounting points, and finish needed.

Pressure forming offers a low tooling cost with the benefits of a higher cost process like injection molding, but requires more after molding machining which will increase the per part price. The estimated tooling cost for a housing of our approximate size would be about $5,400, and could increase in price anywhere from $1,500 – 2,200 depending on the type of finish that would be needed. Because the device location is on the dash and should have as little glare as possible, a textured finish would be needed. Injection molding has a higher tooling cost, however would allow very little or no per part after molding machining. The approximate tooling cost will be about $14,000.

In order to make a final decision on which process to use we will have to wait until internal components, size, and mounting constraints are required. Injection molding would be the optimal choice as far as quality.

8.3 Concept Design & Feasibility

8.3.1 Function After looking at a variety of mounting locations including sun visor, window mount, and rear window shelf, the front dashboard was decided on as the best location. The front dash offers the most usable space because the other locations on many cars are used for other things or are non-existent on some models. This location also does not interfere with the electronic signals coming in.

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Velcro, suction cups, and non-slip pads were among the top materials to be used for mounting on the dashboard. It was decided that a non-slip pad made of a material like silicone, or neoprene would be best. This is because of the secure yet non-permanent non-marking properties it offers. Previous commercial success also proves that it would be a good option. This would also offer the easiest mounting process for the user. The pads are thin which would help fulfill our goal of a small unobtrusive design.

The housing forms were designed around specific functions the device could offer. One concept would be an oval shape that would allow the user to place different colored covers on top to allow the appearance to match the car’s interior color better. Another concept derives its form from the use of solar panels to power the device. This design is at a slight angle to match the angle of most car windshields allowing for better direct sunlight throughout the day. The last suggested concept offers a universal form that can be scaled to fit the needs of the interior electronics. This concept also offers more opportunity for placement of switches and removable panels if such human interaction is required.

Figure 27: Different form concepts

8.3.2 Aesthetics Due to the curved nature of most dashboards a form that would become apart of the dash and not take away from the look of the car interior was needed. All of the form concepts include a sleek form with gestures that mimic the curves of the dash as well as other interior car accessories. Due to the dashboard location, the housing should not be reflective as any glare might interfere with the driver’s vision. Therefore, a textured or matte finish would be needed. Colors could be included to match the car interior, or allow the user to change between different colors. Common colors found were black, navy blue, light tan, and gray.

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9 SENIOR DESIGN II PLAN:

9.1 Board fabrication The final layout for the prototype repeater board will be done over finals week. This is so the board can be fabricated over the thanksgiving break and ready for assembly when winter quarter starts. It is estimated that the board will be no greater than 4 in X 4 in.

If money was not a factor, having more than 2 layers for the PCB would be ideal. Then one layer can be used for ground, and three layers for routing of the circuit. However, the cost of having more than 2 layers is significantly more expensive.

PCB fabrication is not cheap. Price quotes were obtained from two manufacturers and are shown in Table 13. Based on the results, we will be using a two layer board from PCB Fab Express.

Manufactuer PCB Express PCB Express PCB Fab Express PCB Fab ExpressLayers 2 4 2 4Solder Mask ? No Yes Yes YesNumber of boards 2 2 5 5Total Cost $80.00 $250.00 $65.00 $165.00Lead Time 1 day 3 days 5 days 5 days

Table 13: Comparison of PCB manufacturers12

A lot of the parts used are surface mount technology. The surface mount soldering machines in CIMS will be used to build the boards.

9.2 Anticipated problems

9.2.1 Power In portable devices, power is always an issue. Although the power consumption for the repeater will be designed to run off of a set of batteries, this may not happen in actual testing. The actual current draw of the devices used may be higher than specified in the datasheets, and the battery may not last for its specified milliamp hour current rating. This issue cannot be planned for since we can only design with theoretical values and will have to make modifications when testing the actual repeater.

9.3 Prototype testing and modifications

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The first test to be performed on the prototype repeater device will be a functional test. An oscilloscope and Microchip receiver board will be used to view the repeated signal of a key fob device. The captured signal will then be compared to the original key fob signal. If the results are successful, the repeater device will be tested with a real car system.

Four corners test for temperature will be done on the final circuit board to make sure it can operate in a wide temperature range. This can be done in an electric oven. The four corners test is where the operation of the device is tested under the maximum and minimum conditions. The four conditions are operation at minimum voltage and minimum temperature, minimum voltage and maximum temperature, maximum voltage and maximum temperature, and maximum voltage and minimum temperature.

Using a field strength meter, the emissions field strength from the repeater’s antenna during transmission will have to be measured to make sure FCC rule are being followed. The repeater is subject to FCC Title 47 Part 15 Sections 209 and 231. The exact rules can be seen in the appendix in section 10.3 and 10.4.

9.4 Commercialization During senior design two, a foam model of the housing will be fabricated. Once the schematic and layout for the PCB is finalized, the housing will be fabricated out of real material. Packaging for the repeater device will also be made including an instruction booklet.

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10 Appendix:

10.1 House of quality

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10.2 Morphological chart

47

10.3 FCC rules: Part 15 Section 209 Code of Federal Regulations] [Title 47, Volume 1] [Revised as of October 1, 2004] From the U.S. Government Printing Office via GPO Access [CITE: 47CFR15.209] [Page 808-809] TITLE 47--TELECOMMUNICATION CHAPTER I--FEDERAL COMMUNICATIONS COMMISSION PART 15_RADIO FREQUENCY DEVICES--Table of Contents Subpart C_Intentional Radiators Sec. 15.209 Radiated emission limits; general requirements. (a) Except as provided elsewhere in this subpart, the emissions from an intentional radiator shall not exceed the field strength levels specified in the following table: ------------------------------------------------------------------------ Measurement Frequency (MHz) Field strength distance (microvolts/meter) (meters) ------------------------------------------------------------------------ 0.009-0.490...................... 2400/F(kHz) 300 0.490-1.705...................... 24000/F(kHz) 30 1.705-30.0....................... 30 30 30-88............................ 100 ** 3 88-216........................... 150 ** 3 216-960.......................... 200 ** 3 Above 960........................ 500 3 ------------------------------------------------------------------------ ** Except as provided in paragraph (g), fundamental emissions from intentional radiators operating under this section shall not be located in the frequency bands 54-72 MHz, 76-88 MHz, 174-216 MHz or 470-806 MHz. However, operation within these frequency bands is permItted under other sections of this part, e.g., Sec. Sec. 15.231 and 15.241. (b) In the emission table above, the tighter limit applies at the band edges. (c) The level of any unwanted emissions from an intentional radiator operating under these general provisions shall not exceed the level of the fundamental emission. For intentional radiators which operate under

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the provisions of other sections within this part and which are required to reduce their unwanted emissions to the limits specified in this table, the limits in this table are based on the frequency of the [[Page 809]] unwanted emission and not the fundamental frequency. However, the level of any unwanted emissions shall not exceed the level of the fundamental frequency. (d) The emission limits shown in the above table are based on measurements employing a CISPR quasi-peak detector except for the frequency bands 9-90 kHz, 110-490 kHz and above 1000 MHz. Radiated emission limits in these three bands are based on measurements employing an average detector. (e) The provisions in Sec. Sec. 15.31, 15.33, and 15.35 for measuring emissions at distances other than the distances specified in the above table, determining the frequency range over which radiated emissions are to be measured, and limiting peak emissions apply to all devices operated under this part. (f) In accordance with Sec. 15.33(a), in some cases the emissions from an intentional radiator must be measured to beyond the tenth harmonic of the highest fundamental frequency designed to be emitted by the intentional radiator because of the incorporation of a digital device. If measurements above the tenth harmonic are so required, the radiated emissions above the tenth harmonic shall comply with the general radiated emission limits applicable to the incorporated digital device, as shown in Sec. 15.109 and as based on the frequency of the emission being measured, or, except for emissions contained in the restricted frequency bands shown in Sec. 15.205, the limit on spurious emissions specified for the intentional radiator, whichever is the higher limit. Emissions which must be measured above the tenth harmonic of the highest fundamental frequency designed to be emitted by the intentional radiator and which fall within the restricted bands shall comply with the general radiated emission limits in Sec. 15.109 that are applicable to the incorporated digital device. (g) Perimeter protection systems may operate in the 54-72 MHz and 76-88 MHz bands under the provisions of this section. The use of such perimeter protection systems is limited to industrial, business and commercial applications. [54 FR 17714, Apr. 25, 1989; 54 FR 32339, Aug. 7, 1989; 55 FR 18340, May 2, 1990; 62 FR 58658, Oct. 30, 1997]

10.4 FCC rules: Part 15 Section 231 [Code of Federal Regulations] [Title 47, Volume 1] [Revised as of October 1, 2004] From the U.S. Government Printing Office via GPO Access [CITE: 47CFR15.231]

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[Page 813-814] TITLE 47--TELECOMMUNICATION CHAPTER I--FEDERAL COMMUNICATIONS COMMISSION PART 15_RADIO FREQUENCY DEVICES--Table of Contents Subpart C_Intentional Radiators Sec. 15.231 Periodic operation in the band 40.66-40.70 MHz and above 70 MHz. (a) The provisions of this section are restricted to periodic operation within the band 40.66-40.70 MHz and above 70 MHz. Except as shown in paragraph (e) of this section, the intentional radiator is restricted to the transmission of a control signal such as those used with alarm systems, door openers, remote switches, etc. Continuous transmissions, voice, video and the radio control of toys are not permitted. Data is permitted to be sent with a control signal. The following conditions shall be met to comply with the provisions for this periodic operation: (1) A manually operated transmitter shall employ a switch that will automatically deactivate the transmitter within not more than 5 seconds of being released. (2) A transmitter activated automatically shall cease transmission within 5 seconds after activation. (3) Periodic transmissions at regular predetermined intervals are not permitted. However, polling or supervision transmissions, including data, to determine system integrity of transmitters used in security or safety applications are allowed if the total duration of transmissions does not exceed more than two seconds per hour for each transmitter. There is no limit on the number of individual transmissions, provided the total transmission time does not exceed two seconds per hour. (4) Intentional radiators which are employed for radio control purposes during emergencies involving fire, security, and safety of life, when activated to signal an alarm, may operate during the pendency of the alarm condition (b) In addition to the provisions of Sec. 15.205, the field strength of emissions from intentional radiators operated under this section shall not exceed the following: ------------------------------------------------------------------------ Field strength of Field strength of Fundamental frequency (MHz) fundamental spurious emissions (microvolts/meter) (microvolts/meter) ------------------------------------------------------------------------ 40.66-40.70..................... 2,250............. 225 70-130.......................... 1,250............. 125 130-174......................... \1\ 1,250 to 3,750 \1\ 125 to 375

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174-260......................... 3,750............. 375 260-470......................... \1\ 3,750 to \1\ 375 to 1,250 12,500. Above 470....................... 12,500............ 1,250 ------------------------------------------------------------------------ \1\ Linear interpolations. (1) The above field strength limits are specified at a distance of 3 meters. The tighter limits apply at the band edges. (2) Intentional radiators operating under the provisions of this section shall demonstrate compliance with the limits on the field strength of emissions, as shown in the above table, [[Page 814]] based on the average value of the measured emissions. As an alternative, compliance with the limits in the above table may be based on the use of measurement instrumentation with a CISPR quasi-peak detector. The specific method of measurement employed shall be specified in the application for equipment authorization. If average emission measurements are employed, the provisions in Sec. 15.35 for averaging pulsed emissions and for limiting peak emissions apply. Further, compliance with the provisions of Sec. 15.205 shall be demonstrated using the measurement instrumentation specified in that section. (3) The limits on the field strength of the spurious emissions in the above table are based on the fundamental frequency of the intentional radiator. Spurious emissions shall be attenuated to the average (or, alternatively, CISPR quasi-peak) limits shown in this table or to the general limits shown in Sec. 15.209, whichever limit permits a higher field strength. (c) The bandwidth of the emission shall be no wider than 0.25% of the center frequency for devices operating above 70 MHz and below 900 MHz. For devices operating above 900 MHz, the emission shall be no wider than 0.5% of the center frequency. Bandwidth is determined at the points 20 dB down from the modulated carrier. (d) For devices operating within the frequency band 40.66-40.70 MHz, the bandwidth of the emission shall be confined within the band edges and the frequency tolerance of the carrier shall be 0.01%. This frequency tolerance shall be maintained for a temperature variation of -20 degrees to +50 degrees C at normal supply voltage, and for a variation in the primary supply voltage from 85% to 115% of the rated supply voltage at a temperature of 20 degrees C. For battery operated equipment, the equipment tests shall be performed using a new battery. (e) Intentional radiators may operate at a periodic rate exceeding that specified in paragraph (a) of this section and may be employed for any type of operation, including operation prohibited in paragraph (a)

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of this section, provided the intentional radiator complies with the provisions of paragraphs (b) through (d) of this section, except the field strength table in paragraph (b) of this section is replaced by the following: ------------------------------------------------------------------------ Field strength of Field strength of Fundamental frequency (MHz) fundamental spurious emission (microvolts/meter) (microvolts/meter) ------------------------------------------------------------------------ 40.66-40.70..................... 1,000............. 100 70-130.......................... 500............... 50 130-174......................... 500 to 1,500 \1\.. 50 to 150 \1\ 174-260......................... 1,500............. 150 260-470......................... 1,500 to 5,000 \1\ 150 to 500 \1\ Above 470....................... 5,000............. 500 ------------------------------------------------------------------------ \1\ Linear interpolations. In addition, devices operated under the provisions of this paragraph shall be provided with a means for automatically limiting operation so that the duration of each transmission shall not be greater than one second and the silent period between transmissions shall be at least 30 times the duration of the transmission but in no case less than 10 seconds. [54 FR 17714, Apr. 25, 1989; 54 FR 32340, Aug. 7, 1989, as amended at 68 FR 68546, Dec. 9, 2003]

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10.5 Schematics

10.5.1 Maxim Receiver

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10.5.2 ChipCon Receiver

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10.5.3 PIC Schematic

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10.5.4 Saw Filter and Antenna Schematic

10.5.5 Transmitter Schematic

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10.5.6 Comparator Schematic

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10.6 BOM

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10.7 Flowchart Basic operation and flowchart software

10.7.1 High Level Software Flowchart

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10.7.2 Detailed Software Flowchart

11 BIBLIOGRAPHY: Proakis, John, Salehi, Masoud, Fundamentals of communication systems Prentice Hall, Upper Saddle River, New Jersey, 2005. FCC Rules and Regulations: http://www.access.gpo.gov/nara/cfr/waisidx_04/47cfr15_04.html

FCC ID Search: http://www.fcc.gov/oet/fccid/ https://gullfoss2.fcc.gov/prod/oet/cf/eas/reports/GenericSearch.cfm FCC Laboratory contact:

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https://gullfoss2.fcc.gov/prod/oet/cf/kdb/index.cfm SAW Filter: http://www.abracon.com/Filters/SAW%20FILTERS/AFS315E.pdf http://www.abracon.com/Filters/SAW%20FILTERS/afs433e01.pdf http://www.abracon.com/Filters/SAW%20FILTERS/AFS434S3.pdf Sampling Theory: http://www2.egr.uh.edu/~glover/applets/Sampling/Sampling.html Microcontroller Datasheet: http://ww1.microchip.com/downloads/en/DeviceDoc/39626b.pdf Receiver: http://pdfserv.maxim-ic.com/en/ds/MAX1471.pdf http://www.chipcon.com/files/CC1100_Data_Sheet_1_0.pdf Transmitter: http://ww1.microchip.com/downloads/en/DeviceDoc/70091a.pdf

Endnotes: 1 http://www.maxim-ic.com/appnotes.cfm/appnote_number/1774 2 http://en.wikipedia.org/wiki/Manchester_encoding 3 http://www.directed.com/contact/faq.asp?no=11#11 4 http://ww1.microchip.com/downloads/en/DeviceDoc/21137f.pdf 5 http://ww1.microchip.com/downloads/en/AppNotes/00661b.pdf 6 http://www.maxim-ic.com/appnotes.cfm/appnote_number/1773 7 http://nextag.com/solar-cell/search_html 8 http://www.soyter.com/index.php?pid=148 9 http://www.duracell.com/oem/Pdf/others/ATB-5.pdf 10 http://data.energizer.com 11 http://www.mahaenergy.com/store/viewItem.asp?idProduct=400 and http://www.walmart.com and http://www.staples.com 12 http://ecommerce.pcbfabexpress.com/index.jsp and

http://www.pcbexpress.com/products/express1.php