Multi measurement Unit

Authors: Jabran Sajid, Mohammad Rokibul Islam, Sajidur Rahman

Faculty Lab Coordinator: Dr. Vadim Geurkov

April 10, 2014

A Multi-Measurement Unit with the Internet Access

EDP Project Report

Department of Electrical and Computer Engineering Faculty of Engineering and Architectural Science


Jabran Sajid, Mohammad Rokibul Islam, Sajidur Rahman Page 2

Introduction

Measurement devices are very commonly used unit in different aspects of daily life. Es-

pecially in engineering field and research, a measurement unit is a very vital component to be

used. For this project, a multi-measurement unit was designed with different instrumentation

techniques.

Firstly, the measurement unit requires a central processor from which to take in meas-

ured values, display them on an LCD and upload them to a server. For this basic function, the

simplest and most cost-effective device is a microcontroller. In this purpose, ChipKIT WF32

board was selected with a PIC32 micro-processor on board. One of the main reason to pick this

board was it has a built in Wi-Fi module and a SD card facility which can be implemented to

establish the web server and web site for the project. The multi-measurement unit that is going

to be designed in this project is a universal device, which can perform in multiple modes of op-

eration, such as voltmeter, LCR Meter, and oscilloscope. The voltmeter was implemented using

the ADC of the micro-processor.

Fig. 1. Flow diagram representing the Measurement Process

For the LCR meter, different measurement techniques were researched and analyzed. At

the end, it was decided to use three individual circuitry systems to measure inductance, capaci-

tance and resistance. The reason behind this was to make the design comparatively simple,

easily implementable, less time consuming and cost effective. For the webserver, the SD card



facility of the PIC32 was used and a webpage was created with login credential for the client to

access and see the measurement results. The overall, accuracy for all four measurement was

remained significantly acceptable (less than 5%).



Acknowledgements

We would like to acknowledge the inimitable support of our Faculty Lab Coordinator

Dr. Vadim Geurkov. His generous guidance towards the conceptual building of project was al-

ways motivational for us. We would also like to thank Dr. Mahmood Kassam for his guidance

and support. Thanks to Jim Koch for his technical support for the development of the project.

Lastly, we would like offer our gratitude to Electrical and Computer Engineering Department

of Ryerson University for their laboratory and instrumental support for the completion of the

project.



Certification of Authorship

We Jabran Sajid, Mohammad Rokibul Islam and Sajidur Rahman, hereby declare that

we are the authors of this Engineering Design Project report. We also certify that this project

was analyzed, designed and developed with our own research and any additional assistance we

have received in its preparation is fully acknowledged and cited in the paper. We further au-

thorize Ryerson University to use or reproduce this report entirely or partially for the purpose

of scholarly research.

Jabran Sajid _____________________

Mohammad Rokibul Islam _____________________

Sajidur Rahman _____________________



Table of Contents

Introduction ...................................................................................................................... 2

Acknowledgements .......................................................................................................... 4

Certification of Authorship ............................................................................................... 5

Table of Contents ............................................................................................................. 6

Figures and Tables .................................................................................................... 7

Abstract ............................................................................................................................. 8

Objectives ......................................................................................................................... 9

Theory ............................................................................................................................. 10

Voltage Measurement ................................................................................................. 10

LCR Measurement ...................................................................................................... 11

Impedance ................................................................................................................... 12

Measurement Issues .................................................................................................... 13

LCR Measurement Techniques .................................................................................. 15

ChipKIT WF32 Board and PIC32 Microcontroller .................................................... 26

Design ............................................................................................................................. 31

Documentation Including Schematics and Parts Lists ................................................... 37

Measurement and Testing Procedure ............................................................................. 38

Performance Measurement ............................................................................................. 40

Analysis of Performance ................................................................................................ 41

Conclusion ...................................................................................................................... 42

Appendices ..................................................................................................................... 43

References ...................................................................................................................... 74



Figures and Tables

Fig. 1. Flow diagram representing the Measurement Process 2

Fig. 2. A/D Converter Module Block Diagram 9

Fig. 3. Simple Block Diagram of Auto-Balancing Bridge 16

Fig. 4. Signal Source Section Block Diagram 17

Fig. 5. Block Diagram of Simplified Auto Balancing Bridge Section 18

Fig. 6. Block Diagram of Vector Ratio Detector Section 19

Fig. 7. Vector Ratio Calculation Process 19

Fig. 8. Simplified Block Diagram of Dual-Slope ADC 20

Fig. 9. Three Phases of Dual Slope ADC Conversion. 21

Fig. 10. LC Tank Circuit 22

Fig. 11. Wheatstone Bridge 23

Fig. 12. Four Wire Method of Resistance Measurement 24

Fig. 13. Voltage Drop Method 25

Fig. 14. The ChipKIT WF32 Board 26

Fig. 15. Colpitts Oscillator Circuit to Measure Inductance 32

Fig. 16. Astable 555 Timer Circuit to Measure Capacitance 34

Fig. 17. Webpage Display for the Measurement Unit 38



Abstract

This report presents the development of a microprocessor based multi-measurement unit

with data transfer capability from the microprocessor to the internet wirelessly. A chipKIT

WF32 board was used in this project with a PIC32MX695F512L on board. The measurement

unit was designed to compute: capacitance, inductance, resistance, voltage. The design was

completed in two phases: hardware designing and software designing. In the first phase, the

hardware setup was developed for inductance measurement using resonant frequency method,

capacitance measurement using 555 timer oscillation circuit, and resistance measurement using

voltage drop process. The completion of the project was apprehended successfully. The final-

ized design was capable of measuring voltages from (+ve) 4V to (-ve) 4V, resistance from 1

k to 15 k, capacitance from 1 F to 1 mF, and inductance from 1mH to 1H with a maxi-

mum error of less than 5%. The webserver and the webpage were also established to view the

result remotely via internet access.



Objectives

The major objective of this Engineering Design Project is to understand, design and im-

plement a multi-measurement unit with internet access. The entire project is needed to develop

in two distinctive unit: the measurement unit and the PC based computational unit. At the most

basic level, the measurement unit must be able to take in measurements as- a logic analyzer, an

analog voltmeter and a LCR meter. Then the PC based unit will receive the information and

will relay on a local display via a LCD display and will upload to an online server. Lastly, the

data on the server must be accessible remotely through an online interface and can be con-

trolled as well.



Theory

Voltage Measurement

Voltmeter is a measurement device used for obtaining the potential difference or volt-

age between two points in an electrical circuit. It takes in the voltage of a point with respect to

the ground and takes in the voltage reading from another point, and then displays the compared

potential difference between these two points.

Measuring voltage with an analog multimeter is a very commonly used task in the field

of electrical research. However, it is possible to measure analog voltage with a microprocessor

by converting it into digital signal. Present days, microprocessor are provided with a special

feature called ADC (Analog-to-Digital Converter) which allows to perform this operation. The

operation is completed in two stages: acquisition and conversion.

Fig.2. A/D Converter Module Block Diagram



In the first stage, the microprocessor reads the analog voltage provided by a power sup-

ply. It should be mention that, micro-controllers have limitations while receiving the voltage as

most of cannot read more than 5V generally (with exceptions). Often, sample and hold (S&H)

capacitor is used to the match the voltage with the input pin voltage of the microprocessor. This

S&H capacitor converts the voltage to readable binary input for the microprocessor. In the case

of PIC32 series microprocessor, the conversion process is carried on with a successive approx-

imation register (SAR) register. A successive approximation ADC compares the pins voltage to

an internal analog voltage generated by an internal digital-to-analog converter. The DAC volt-

age will be incremented until a match is found. When this happens, the 10-bit value used to

drive the DAC becomes the 10-bit analog value. The PIC32 ADC has its own clock with a pe-

riod which can be configured by the user.

LCR Measurement

An inductor acts as a passive electronic component made of a conductor wounded into a

coil. When electricity starts to flow through the coil, it stores electrical energy by generating a

magnetic field. Inductance of any material depends on the radius of the coil and on the wound-

ing material used. Higher valued inductors are used in the power supply of different electronic

devices to resist any change in the amount of current flowing through it.

Capacitor is a very important component used in different electronic circuits- such as, in

timer circuit or to smooth a current to prevent false triggering of other components such as re-

lays. It is basically a passive electronic component consisted of two conducting plates separated

by an insulating material (dielectric) that stores energy in the form of an electrostatic field. The

accuracy of a capacitor measurement may vary due to different physical characteristics of the



capacitance elements. In generally, capacitors are tend to have higher temperature coefficients

Also, the room temperature of the laboratory or the test DUT temperature drift can cause error.

Moreover, the system parasitic as well as the noise from surrounding could also affect the re-

sult, especially in higher frequency.

Resistors are basically an electrical component to resist the flow of electric current. It is

considered as one of the most important element for any circuitry presents in the modern elec-

trical devices and it has a very wide range of uses.

Impedance

Electrical impedance (Z) is an expansion of the concept of resistance in electric circuits.

It can be defined as the total opposition or prevention which can be offered by an electrical cir-

cuit or component against the alternating current (AC) flows through the circuit, at a given fre-

quency. It changes according to the components used in the circuit. Impedance is a very com-

monly used parameter in the electric circuitry; consisted of resistance (R), inductive reactance

(XL), and capacitive reactance (XC). However, impedance is not the algebraic combination of

the resistance, inductive resistance, and capacitive reactance present in a circuit. Taking re-

sistance as the reference (which is always in phase with the applied voltage), both capacitive

and inductive reactance are 90 degrees apart from phase angle of the resistance.

For a DC supply, resistance (R) is generally defined by the ratio of the voltage (V) to

the generated current (I) due to the supply voltage. Therefore, according to Ohms law, Re-

sistance, R= V/I. For an AC supply, the current produced by the AC voltage keeps changing its

polarity in a regular fashion. Therefore, if there is either capacitive resistance or inductive re-



sistance, or both are present in the circuit, then the Ohms law is needed to be modified accord-

ingly. The impedance for a series model in an AC circuit is referred by:

Z = V/I = R + jX.

Here, Z is a complex number consisted of two significant terms, R (real component of

impedance) and X (imaginary component of impedance). In another word, R denotes resistance

and X denotes reactance. In a similar way, for a parallel model, admittance is used instead of

impedance; Y=G+jB, where G is conductance and B is referred as susceptance. Unlike re-

sistance, reactance actually changes with the variation of frequency of the AC signal. There are

two types of reactance: capacitive reactance (Xc) and inductive reactance (XL).

The total reactance, X = XL - Xc.

To mention, capacitive and inductive reactance have somewhat opposing characteristic:

at lower frequency, capacitive reactance is usually large at lower frequencies and small at high-

er frequencies; whereas, the inductive reactance tends to behave in opposite manner.

Measurement Issues

Different methods and measuring instruments can cause variation in results of imped-

ance measurement. Therefore, when measuring different parameters (such as, voltage, re-

sistance, capacitance, inductance etc.) of an electric circuit, there are several factors which

needed to be acknowledged.

Component Parasitics

The standard values of resistive, inductive and capacitive components are normally rep-

resented by the nominal values of respective components at a given condition. However, purely

resistive or reactive components do not exist in reality. They have different parasitics depend-



ing on the materials and manufacturing process were used in production of those component. In

fact, many parasitics reside in components and affect both the usefulness and precision of com-

ponents. The quality factor Q represents the non-ideal characteristics of any component. The

higher the Q is, the better or more ideal would be the component.

Test Frequency

Due to the existence of parasitics, generally all the test components are affected by the

test frequency. In case of capacitor measurement, capacitor tends to act as a capacitive compo-

nent at lower frequencies. Actually, self-resonant frequency of any component determines the

maximum usable frequency of that particular component. When the capacitor frequency re-

sponse reaches to its self-resonant frequency, the capacitive and inductive reactance of the

component became equal and it acts as a resistor. When it passes the self-resonant frequency,

the phase angle gets closer to positive 90 degrees and the component acts as a inductive re-

sistance due to the dominance of inductive parasitics. Similarly, the inductor has a maximum

impedance point at the self-resonant frequency due to the presence of parasitics capacitance. In

the low frequency region below the resonant frequency, the reactance is inductive. After the

resonant frequency, the capacitive reactance due to the parasitic capacitance is dominant.

Test signal level

The AC signal applied through the DUT may affect the measurement result. Specially,

for surface mounted devices, test signal level is a very significant dependency factor. Consider-

ing the case of fixed valued ceramic capacitors, the measurement results get affected with the

increment of the test signal voltage. This dependency differs with the variation of the dielectric

constant (K) of the material that is used in the ceramic capacitor. As for inductors, measure-



ment result depends on the current produced by test signal due to the electromagnetic hysteresis

of the core material. For, a high test signal level, an excessive distorted signal may pass through

the terminal and may cause unbalance.

DC Bias

Both capacitor and inductor shows DC bias dependency in different cases. The capaci-

tance of a high-K type dielectric ceramic capacitor changes depending on the applied DC bias

voltage. In the case of cored-inductors, the inductance changes depending on the DC bias cur-

rent flowing through the coil, due to the magnetic flux saturation characteristics of the core ma-

terial.

Test Fixture

The accuracy of measurement also depends on the test fixtures used. A test fixture is ac-

tually a set up or device used to hold or connect the DUT for the testing process. As example,

metal probes would be used in the case of this project to connect with the two end of different

resistive components (resistor, capacitor or inductor). When the probes or any other conducting

materials are come to contact with an inductor, eddy current starts to flow due to relative mo-

tion of the field source and conductor. These circulating eddies of current have inductance and

thus induce magnetic field which in turn results in deviated inductance values during measure-

ment process.

LCR Measurement Techniques

Measuring impedance of any component can be performed using numerous methods

and technologies. However, each of them comes with distinctive advantages and disadvantages.



Therefore, different significant criteria are necessary to keep in mind while apprehending a

measuring technique for this project. The major factors would be the frequency range within

the test will be performed, the physical characteristics of the DUT and its impedance measure-

ment range, the precision of the measurement, and test conditions. Moreover, the facilities and

easiness of implementation, and cost effectiveness of designing materials are one of the most

compelling factors for the selection process. In cases, one individual method may be suitable

for measuring inductance, but not highly viable for measuring capacitance or the other way

around. Therefore, it may be necessary to implement different methods or combining tech-

niques to design the complete measurement unit. Different measurement techniques are being

described in the following sections:

Auto Balancing Bridge Method

The auto balancing bridge technique is one of the most prominent methods to measure

impedance at any frequency lower than 40 MHz. It renders possibly the most precise measure-

ments with broad measurement range. To measure the complex impedance of the DUT, two

parameters are needed to be measured- the voltage of the test signal applied to the DUT and the

current that flows through the DUT. Keeping the concept in mind, the circuit for auto balancing

method is built with a signal source, a high gain operational amplifier, a voltmeter, and an am-

meter as shown in Fig. 3.



Fig. 3. Simple Block Diagram of Auto-Balancing Bridge

For lower frequencies, auto-balancing bridge will use a current to voltage (I/V) convert-

er circuit which includes an operational amplifier with a negative feedback loop instead of the

ammeter. The bridge section determines the impedance by sending the test signal current Ix

which flows through the DUT and in turn flows into the converter. The same amount of current

(Ir) then flows back through the resistor (Rr) as negative feedback. The I/V converter output

voltage (Vr) can be represented by the following equation:

Vr = Ir Rr = Ix Rr

Ix is determined by the following equations:

Ix = Vx / Zx

The equation for impedance (Zx) can be derived from the above two equations as fol-

lowing:

Zx = (Vx / VR) Rr

Therefore, the whole circuit is actually divided into three sections depending on their

functionality: signal source section, auto balancing bridge section, and vector ratio detector sec-

tion.



Fig. 4. Signal Source Section Block Diagram

The signal source section generates the test signal that passes through the DUT. The

frequency of the generated signal varies from 40 Hz to 110 MHz. This signal passes through a

source resistor and gives output at Hc terminal which is connected to the input of the DUT. In

the case of a microprocessor, both the initial signal (source) and internal reference signal can be

generated with an integrated oscillator or the microprocessor. Frequency synthesizer and fre-

quency conversion techniques are used to generate high-resolution test signals with a minimum

resolution of 1 mHz.

The auto-balancing bridge section balances the range resistor current with the DUT cur-

rent while maintaining a zero potential at the Low terminal. When the range resistor current (Ir)

is not balanced with the DUT current (Ix), an unbalance current which is the difference between

Ix and Ir, flows into the null detector at the Lp terminal. The unbalance current vector represents

how much the magnitude and phase angle of the range resistor current differ from the DUT cur-

rent. The null detector detects the unbalance current and controls both the magnitude and phase

angle of the second oscillator output to assure that the detected current is zero (null).



Fig. 5. Block Diagram of Simplified Auto Balancing Bridge Section

Low frequency instruments, below 100 kHz, employ a simple operational amplifier to

configure the null detector. To mention, this particular circuit configuration can be used for fre-

quencies less than 100 kHz, as the operational amplifier has performance limitation above that

frequency range. The instruments that cover frequencies above 100 kHz have an auto balancing

bridge circuit consisting of a null detector, a phase detectors, and a vector modulator. When an

unbalance current is detected with the null detector, the phase detectors in the next stage sepa-

rate the current into 0 and 90 vector components. The phase detector output signals go

through integrators (loop filters) and are applied to the vector modulator to drive the 0 or 90

component signals. Next, the component signals are compounded and the resultant signal is fed

back through range resistor (Rr) to cancel the current flowing through the DUT. In the case of

the balancing control loop having phase errors, the unbalance current component can also be

detected and fed back to cancel the error in the range resistor current. Thus, the unbalance cur-

rent becomes nullified to assure that the current passing through the DUT and the current pass-

ing through the range resistor remain up to 110 MHz.



Fig. 6. Block Diagram of Vector Ratio Detector Section

The vector ratio detector section processes the ratio of vector voltages across the DUT

(Vx), and voltage across the range resistor (Vr). This sections has an input selector switch (S), a

phase detector that detects phases between 0 to 90, and an Analog to Digital converter. The

measured vector voltages are used to calculate the complex impedance (Zx). The following dia-

gram shows the vector ratio calculation process of the voltages:

Fig. 7. Vector Ratio Calculation Process

The problem with this method is when the frequency is too high or when the cable

length is too long, the bridge circuit cannot perform the automatic balancing; as a result, the



unbalance current cannot be nullified. Also, the impedance measurement range is quite limited

due to the existence noise level.

Dual Slope ADC Method

A very popular method to measure capacitance and inductance is by using a dual slope

ADC method. The dual slope conversion takes place in three distinct phases: auto zero phase,

signal integration phase and reference integration phase.

In the auto-zero phase, the errors in the analog components (e.g. buffer offset voltages)

will be automatically nulled out by grounding the input and closing a feedback loop such that

error information is stored on an auto-zero capacitor.

Fig. 8. Simplified Block Diagram of Dual-Slope ADC

The signal integration phase will start the real conversion process. The input signal

would be integrated for a fixed number of clock pulses. For a 31

2-digit converter, 1,000 pulses is

the general count. On completion of the integration period, the voltage VREF is directly propor-

tional to the input signal.



Phase 3, Reference Integrate. At the beginning of this phase, the integrator input is

switched from VIN to VREF. The polarity of the reference which was determined during Phase 2

such that the integrator discharges back towards zero. The number of clock pulses counted be-

tween the beginning of this cycle and the time when the integrator output passes through zero is

a digital measure of the magnitude of VIN.

Fig. 9. Three Phases of Dual Slope ADC Conversion.

The effective part of the dual slope technique is that the theoretical accuracy depends

only on the absolute value of the reference and the equality of the individual clock pulses with-

in a given conversion cycle. The latter can easily be held to 1 part in 106, so in practical terms

the only critical component is the reference. Changes in the value of other components such as

the integration capacitor or the comparator input offset voltage have no effect, provided they

dont change during an individual conversion cycle. This is in contrast to Successive Approxi-

mation converters which rely on matching a whole string of resistor values for quantization

Although, this method has the advantage of simplicity and precision, it also comes with

following design limitations which can cause deviation in the measurement process:



Dielectric absorption of the integrator capacitor must be compensated, even with high-

quality integrator capacitors, which can require complicated calibration procedures.

The signal must be gated on and off, as must the reference. This process can introduce

charge injection into the input signal. Charge injection can cause input-dependent errors

which are difficult to compensate for at very high resolutions.

The ramp-down time seriously degrades the speed of measurement. The faster the ramp

down, the greater the errors introduced by comparator delays, charge injection, and so on.

Some topologies use a trans-conductance stage prior to the integrator to convert the voltage

to a current, and then use current steering networks to minimize charge injection. Unfor-

tunately, this added stage introduces complexity and possible errors.

Resonant Frequency Method

The concept of this method actually was derived from the idea of resonant frequency.

The natural frequency of any physical system or object are the frequencies at which it will vi-

brate if physically disturbed. However, resonance is the phenomenon that occurs when a physi-

cal system is periodically disturbed at the same period of one of its natural frequencies. The

very particular frequency at which resonance occur for a system is defined as the resonant fre-

quency of that system.

Fig. 10. LC Tank Circuit



In general, a condition of resonance can be met with the help of a LC tank circuit with a

set of capacitor and inductor of equal value. As, the inductive reactance of the inductor increas-

es with increasing frequency and capacitive reactance of the capacitor decreases with increas-

ing frequency; at a common resonant frequency both of the reactance would share an equal

physical value which can be profound by the following formula:

= 1

2

Using this concept, if an unknown inductor is connected in series with the existed in-

ductor, or a capacitor is connected in parallel with both the inductor and capacitor of the tank

circuit; in both cases a different resonant frequency will develop. By comparing the initial res-

onant frequency with the new frequency (due to the attachment of unknown DUT), it is possi-

ble to measure the value of the capacitor or inductor.

Resistance Measurement

There are numerous methods for measuring solely the resistance; such as- Wheatstone

bridge method, auto balancing bridge method, four wire resistance method, voltage drop meth-

od etc. Both the Wheatstone bridge and its modified version (auto balancing bridge) use the

similar concept of maintaining the resistance ratio between the bridges to be equal.

Fig. 11. Wheatstone Bridge



For the above circuit, the ratio would be: 12

=3

Here, Rx is the unknown resistor to be measured. If R1 and R2 are of equal value, then Rx will

be equal to R3. The major issue with this method is the nullification of the bridge as well as

high inaccuracy compare to other methods.

The four wire method of measurement is preferred for resistance values below 100.

From the name it is clear that four different wires are used to measure resistance via this pro-

cess. Two of the wires carry the source or lead current and test current through the R. The other

two wires known as the sense or potential leads, are used to sense the voltage drop across R.

The volt drop across the ohmmeters sense terminals is therefore virtually the same as the volt

drop across the unknown resistor. The disadvantage of this method is it can measure up to

100 resistance.

Fig. 12. Four Wire Method of Resistance Measurement



Voltage Drop Method

It is probably the simplest yet quite accurate way of measuring resistance. From, Ohms

law, it is known that, if two resistors are connected in series after a voltage source, then the

generated voltage get dropped accordingly at output depending on the value of the resistors by

using the following formula:

= (2

1 + 2) 2 = (

) 1

Fig. 13. Voltage Drop Method

If both the input and output voltages and R1 is known, then it is a very straight

forward approach to obtain the value of R2 (DUT).

ChipKIT WF32 Board and PIC32 Microcontroller

PIC microcontrollers (Programmable Interface Controllers), are electronic circuits that

can be programmed to carry out a vast range of tasks. They can be programmed to be timers or

to control a production line and much more. They are found in most electronic devices such as

alarm systems, computer control systems, phones, in fact almost any electronic device. THE

ChipKIT WF32 is a prototyping platform based on Arduino with PIC32 microcontroller

onboard. The PIC32MX695F512L microcontroller comes with a 32-bit MIPS (Microprocessor



without Interlocked Pipeline Stages) based processor core running at 80 MHz, SRAM (Static

random-access memory) data memory of 128K and a flash memory of 512K. It has an installed

Wi-Fi MRF24 module and a micro-SD card module with distinctive signal. For its low price,

wide range of application, high quality and easy availability, it is an ideal solution in applica-

tions such as: the control of different processes in industry, machine control devices, measure-

ment of different values etc. It has a wide range of operating frequency that could be highly ap-

preciable for this project as the measurement range is quite dynamic.

Fig. 14. The ChipKIT WF32 Board

ChipKIT WF32 also features a USB serial port interface for connection to the MP IDE

and can be powered via USB or by an external power supply. It also provides with 43 available

I/O pins and 12 dedicated analog inputs. The serial communication port on the WF32 board is

enacted using an FTDI FR232RQ USB serial converter. The MPIDE uses a serial communica-

tions port to communicate with a boot loader running on the WF32 board. The serial port on the



WF32 board is implemented using an FTDI FT232RQ USB serial converter. The WF32 board

has a standard mini-USB connector. Every time before the connection between MPIDE and

WF32 board is established, the board is reset and activates the boot loader. The MPIDE then

establishes communications with the boot loader and uploads the program to the board. To

open the serial communications connection on a PC, the DTR pin on the FT232RQ chip is set

to low and thus the microcontroller is reset and it initializes the process with boot loader. How-

ever, if necessary, then this auto reset operation can be disabled via a jumper JP1 by unshorten-

ing it. There are two LEDs (LD1 and LD2) present in the board which blinks when data trans-

fer between the WF32 and the PC over the serial connection is in process.

The WF32 board can also use an external power supply via J14 of J17 pin. The power

supply section provides with a 3.3V and a 5V voltage regulators. The 3.3V regulator is used to

power up the board and to perform any internal operation; whereas, the 5V supply is dedicated

to any external circuits or shields. In fact, The WF32 can be operated as a self-powered device

or as a bus powered device from either the USB serial connector (J1) or the USB OTG/device

connector (J12). The jumper block (J15) is used to select the power source to be used to power

the board.

It also comes with a micro-SD card connector to access data stored on micro-SD sized

flash memory cards using the SD card library provided as part of the MPIDE software system.

Dedicated SPI interface on PIC32 microcontroller pins are used to access the SD card. The

most important function of the SD card is it can be used as the store for server. After writing

any HTTP Web server hosting page in a HTML editor, it can be saved and keep functional by

plugging in the SD card in the ChipKIT boards SD card slot and implementing necessary pro-

gramming.



Wi-Fi Module

The WF32 comes with a microchip MRF24WG0MA 802.11 b/g compatible Wi-Fi in-

terface. The firmware of the interface provides the 802.11 network protocol support. The

DNETcK and DWIFIck libraries present the TRP/IP network protocol support for the Wi-Fi

module. The module can keep up to 25 MHz of SPI clock speeds. The interface to the Wi-Fi

module also includes a reset signal, an interrupt signal and a hibernate signal. The active low

RESET signal is used to reset the Wi-Fi module. The INT signal on the Wi-Fi module is con-

nected to external interrupt INT4 on the PIC32 microcontroller. The active low hibernate signal

is used to power the Wi-Fi module down and to keep it in a low power state.

SPI

The synchronous serial port can be accessed using the SPI standard library. Pin 10, 11,

12 and 13 are dedicated for this purpose. Jumpers JP6 and JP7 are used to select the operation

mode: a Master (transmit on MOSI, receive on MISO) or a Slave (transmit on MISO, receive

on MOSI) device. The shorting blocks on JP6 and JP7 are normally placed in the Master posi-

tion for the WF32 to function as an SPI master. Jumper JP3 is used to select PWM output or the

SPI SS function on Pin 10. The shorting block on JP3 should be in the PWM position to select

PWM output. It should be in the SS position to select the SPI SS function.

A/D Converter

The PIC32 has a 10-bit Analog-to-Digital Converter (ADC) with a capacity of up to 1

Msps conversion speed and has 16 analog inputs. It uses a Successive Approximation Register

(SAR) conversion method. It also has two analog input pins for external voltage reference con-



nections which is allowed to share with other analog input pins. The analog inputs are connect-

ed through two multiplexer. The analog input MUXs can be switched between two sets of ana-

log inputs between conversions. Unipolar differential conversions are possible on all channels.

The left-most outer pin on connector J5 is used to provide an external voltage reference to de-

termine the input voltage range of the analog pins. The maximum voltage that can be applied to

this pin is 3.3V. This pin can also be used as digital pin 42. The 10-bit ADC is connected to a

16-word result buffer. Each 10-bit result is converted to one of eight 32-bit output formats

when it is read from the result buffer.

Server

A server is a computer system designed to process requests and deliver data to other

computing system (client) computers over a local network or the Internet. Web server applica-

tions provide network access to Web pages and other intranet and Internet content. Server can

refer to either software or software server system. The typical server is actually a scheme where

a user or client approaches and requests for particular services and the server carries on the ser-

vice accordingly.

In a client-server environment, each computer has some resources which can be ac-

cessed through the other computers. Also, a particular computer can act as a resource centre or

storage from where the other computers can access them. PIC32 microprocessor has a pre-built

application system that includes FreeRTOS, embDUAL (IPv4 and IPv6 TCP/IP stack) and

embHTTP. Instructions are provided to download the pre-build binary, program the PIC32

flash memory, and interact with the demo using a standard web browser. For this project, a

server will be established to store the measurement data in the internet webpage, which can be



accessible by the clients or users with authentic credential. The server is capable of sending and

receiving data from the microprocessor to the webpage.

Design

As it is a multi-measurement unit; hence, 4 different measurements are processed in

four different states. Each state can be selected using designated switches provided in the

measurement unit board. Pin A2 is set for selecting voltage measurement, pin A3 for resistance,

pin A4 for capacitance and pin A5 for measuring inductance. The four switches themselves are

connected with pin A0 of the microcontroller. Pin A6 to A11 are initialized as output pins.

Voltage measurement

The PIC microcontroller used in this project is a PIC32MX695F512L that has 16 analog

input pins for the in-built 16-bit ADC. The voltage to be measured is fed to one of the 16 ana-

log channels. PIC32 has a range of voltage between 0V-3V. To match with the input range an

instrumentation amplifier is used just before the input voltage. The initial supply voltage is fed

through the negative input of the amplifier. A reference voltage, Vref was sent through the posi-

tive input. R1 and R2 were selected as 9890 and 991 respectively. In this process, even

negative voltage is possible to handle. The following formulation was used to adjust the input

voltage:

= (1 +2

1) (

2

1) ; = (

10) + 2.11

This output voltage was then fed to the ADC input and then the microprocessor calcu-

late the actual input voltage using the following formula:

= ( 2.11)(10)



The resultant voltage is then displayed in the LCD of the measurement unit.

Inductance Measurement

After much researching and cost analysis, it was decided that the resonant frequency

method would be chosen to measure inductance. Colpitts Oscillator was used for this purpose

as it consists of a similar parallel LC resonator tank circuit, which has configuration with less

self and mutual inductance in the circuit, and provides more stable frequency at output. How-

ever, in the LC circuit there instead of a single capacitor, Colpitts oscillator uses two capacitors

in series which actually acts a capacitor based voltage divider. The oscillating frequency which

is a pure sine-wave voltage is determined by the resonance frequency of the tank circuit. When

the power supply is connected with to the junction of the capacitor C1 and C2, they get charged

up and then discharged through the coil (inductor). The frequency of oscillations for is deter-

mined by the resonant frequency of the LC tank circuit:

= 1

2

Here, CT is the equivalent capacitance of the series connected C1 and C2:

=

121+2

The amount of the feedback will depend on the values of the two capacitors; the feed-

back will be higher with small valued capacitors. There were options to choose either bipolar

junction transistor (BJT) as the amplifiers active stage of the Colpitts oscillator, or an opera-

tional amplifier. However, the op-amp based Colpitts oscillator was chosen as it was simple to

design and the gain for the op-amp circuit depend on the input and feedback resistors; no other

circuit elements have any effect on it.



Fig. 15. Colpitts Oscillator Circuit to Measure Inductance

At inverting mode, the op-amp used R1 = 1 k as input resistor and R2 = 100 k as the

feedback resistor. Therefore, the gain was obtained as, A= 2

1 = 100. The capacitor values

were chosen as C1=C2= 1F and CT = 0.5 F.

Pin A5 of the microcontroller was used as the input which was connected to the Vout of

the oscillator circuit. XR2206 function generator was used as an external oscillator was to pro-

vide high quality sine waveform (0-3 V at 9V DC input) of high-stability and accuracy. The

frequency value for the initial parallel LC circuit is measured and stored. Then the unknown

inductance Lx is connected and the new frequency is received by the microprocessor. Then both

the frequencies are processed and the value of the inductance is achieved. The output values are

then displayed in the LCD as well as the value would be wirelessly uploaded to the webpage

created for this project.



Capacitance Measurement

In general, capacitance is used as a very common and significant component in deter-

mining the frequency of various oscillatory circuits. In this project, an astable multivibrator 555

timer IC was used to apprehend the frequency of an oscillation which then use to find the un-

known capacitance used in the designed circuitry. 555 timer has a broad frequency output rang-

es which mostly depend on the two resistors and the timing capacitors used in the circuit.

The frequency of oscillation for the 555 timer circuit can be derived from the

following formula:

=1.44

(1 + 22)

The values for R1 and R2 were taken as 66.7 k and 67 k respectively which were al-

most equal. To improve the duty cycle of the 555 timer, a diode was added in parallel with R2

which change the frequency equation to:

=1.44

(1 + 2)

For an unknown capacitor C (which is actually the timer capacitor of the 555 timer cir-

cuit) is connected for measurement purpose; a pulse will send be sent through the 555 timer. It

will produce an output pulse with a certain frequency which will be taken as input via A5 pin of

the PIC32. The microprocessor will count the value of the frequency and from the above for-

mula calculate the value of the capacitor and will output in the LCD as well as to the webpage

designed for the project.



Fig. 16. Astable 555 Timer Circuit to Measure Capacitance

Resistance Measurement

For the designing of the resistor measurement system, the voltage divider is implement-

ed with a known small valued shunt resistor of 1.058 . The reference voltage will be meas-

ured by the microprocessor using the process described in the previous voltage measurement

section. In the next step, the voltage divider equation mentioned in the theory section will be

used to calculate the unknown resistance of the DUT. However, while measuring the resistance,

it was appeared that the voltage across the shunt resistor was very small (0.32 mV) which was

not possible to read by the microprocessor accurately. To solve this issue, an instrumentation

amplifier was connected in parallel to the shunt resistor. The amplifier will initially increase the

gain of the output voltage across the shunt resistor. The gain of the amplifier could be measured

by the following formula:

=49400

+ 1; where RG = 55, is the resistor connected in between the positive and

the negative power supply of the amplifier. Using this amplified voltage, the microprocessor



will calculate the output voltage using the following formula and then will use it to find the

value of the unknown resistance.

= (+ )() = (0.32 0)(899)

Web Server and Site Design

The web server was set up using the chipKITs built in SD card facility. First the server

was created using HTML and then it was copied to the SD card. It is needed to confirm that any

links which was specified in the web pages should be relative to the current page, or relative to

the root of the SD file system. The website was built using the basic HTML with the JavaScript

support to send and receive data from the internet. The chipKIT WF32 board can be connected

with a router using the Ethernet port present in the board. The server is running from the board.

Whenever, the board does any measurement, it stored in a variable inside the html file which is

inside the SD card. With the help of Wi-Fi module in the board, is connected to the router by

matching the SSID which is already programed in the board and the pass phrase. Basically, Wi-

Fi module scan all the Wi-Fi networks and connects to the appropriate networks. After the con-

nection is made, the Wi-Fi module, starts listening to the pre-defined IP address, at which point

the web server goes online. The variables which are stored in the html file (V, R, L, C) and the

current state. And they are being displayed in a table format in the webpage. The main HTML

file refreshes every 2 seconds to get the updated value.



Documentation Including Schematics and Parts

Lists

Component Model / Details

Micro-processor Board ChipKIT WF32

Micro-controller PIC32MX695F512L

555 Timer IC LM511

Function Generator XR2206

Switch PBS-26

Operational Amplifiers LM741, LM314, AD620



Measurement and Testing Procedure

As mentioned earlier, the measurement unit has four different states for four distinctive

parameters. Each states are selected with a push button switch. At every push, it changes one

state and it follows as: voltage resistance capacitance inductance. Therefore, a single

push initiates the first state (voltage measurement), consecutive two pushes initiates the second

state (resistance measurement), and third and fourth state activate with three and four pushes

respectively. If a user wants to move to the capacitance measurement directly (without measur-

ing the first two parameters), the switch is needed to be pushed thrice. At the hardware side,

when any DUT is connected to the measurement probe, the switch is pushed for respective

number of times. As soon as the state is selected, the particular measurement circuitry will be

activated and the function generator will supply a pulse through that circuit. For the voltage

measurement, the microprocessor will measure the voltage via ADC and display it in the LCD.

In the similar fashion, whenever any DUT will be connected to the measurement probe, the

particular type of measurement (inductance, resistance or capacitance) will be displayed in the

LCD.

These results can be seen from the website created for this project. Any user (client pc)

with the login credential can access the website. The website contents a table consisted of the

measurement results which will be updated automatically time to time. Whenever a state is se-

lected, it will be highlighted in the table and the data will be displayed. At the very same time, a

graphical representation of the output pulse will be displayed in the webpage which was devel-

oped using JavaScript.



Fig. 17. Webpage Display for the Measurement Unit



Performance Measurement

Voltage

Range % error

(+ve) 4V (-ve) 4V Less than 3%

Resistance

Range % error

1 k - 15 k Less than 3.5%

Capacitance

Range % error

1 F 1 mF Less than 5%

Inductance

Range % error

1 mH 1 H Less than 3%



Analysis of Performance

From the performance measurement section, the accuracy of the results were within a

reasonable accuracy range. In all four cases of measurements, the measured values had less

than 5% of accuracy. The frequency range for this measurement could have been improved us-

ing different values of resistor with relay or CMOS switches which would reroute the supply

voltage to a different set of resistor set (that can handle that higher or lower range of frequency).

Voltage values were fairly close to the actual input values. In the case of webpage, the tables

were updated in an acceptable manner. However, the output voltage graph was not fair enough

to consider.



Conclusion

The project was focused on the measurement unit with multi-functionality with internet

access. To choose the right method for the measurement as well as the server and Wi-Fi mod-

ule development, a great deal of research was apprehended. The measurement parameters were:

voltage, inductance, capacitance and resistance. After the completion of the measurement unit,

the results we had received were with in an acceptable percentage error. The measurement

range for all four components were for voltage, (+ve) 4V to (-ve) 4V; for resistance, from 1 k

to 15 k; for capacitance, from 1 F to 1 mF; and for inductance from 1mH to 1H. The internet

access for the results was established successfully with the aid of the SD card system and Wi-Fi

module of the ChipKIT WF32 board. The frequency range could have been higher with a dif-

ferent configuration of the resistor set used in the measurement units circuitry; however, for

that relays or switch should have been implemented. Overall, the design project appeared to be

successful in terms of the final result and the learning aspects.

This engineering designing project was a practical experience of a typical designing

process for an engineer. There are some aspects of engineering field in real life which were ex-

perienced through this project. Throughout this project, we have learnt to research and analyze

different measurement processes, the combinational approach of hardware and software devel-

opment, and the different sides of a professional report writing techniques. Moreover, it al-

lowed us to learn team-work, time management, cost minimization, managerial experience as

well. In the conclusion, it can be said that the designing of this multi-measurement unit was a

valuable experience for the final year students; as it would vastly help us to implement our the-

oretical knowledge in practical engineering field.



Appendices

Code for measurement unit

#include

#include

#include // MRF24WG WiFi transceiver -- also use for the

WF32

#include

#include

#include

LiquidCrystal lcd(9, 8, 7, 6, 5, 4);

const int chipSelect_SD_default = 51; // Change 10 to 53 for a Mega

const int chipSelect_SD = chipSelect_SD_default;

static const char szHTMLRestart[] = "GET /Restart ";

static const char szHTMLTerminate[] = "GET /Terminate ";

static const char szHTMLReboot[] = "GET /Reboot ";

static const char szHTMLFavicon[] = "GET /favicon.ico ";

static const char szHTMLSample[] = "GET /Sample ";

GCMD::ACTION ComposeHTMLSamplePage(CLIENTINFO * pClientInfo);



/// State Variables

int x=0,count=0,count2=0;

/// Voltage Variables

float v=0,vactual=0,vref=1.918,r1=9890,r2=991;

/// Resistance Variables

int samples=100;

float vr=0,g=49400/55+1,rshunt=1,iactual=0,vrref=3.245,R=0;

/// Capacitance Variables

float fc=0;

float rc1=465,rc2=463,C=0,CmF=0,CuF=0,CnF=0;

//float r1=66700, r2=67000;

/// Inductance Variables

float fi=0, fave=0, w=0, w2=0, CT=0.5*pow(10,-6),L=0,LmH=0;

/// File declarations

File dataFile;

void setup()



{

Serial.begin(9600);

Serial.print("Initializing SD card...");

lcd.begin(16,2);

pinMode(A2, INPUT); // Voltage

pinMode(A3, INPUT); // Resistance

pinMode(A4, INPUT); // Capacitance

pinMode(A5, INPUT); // Inductance

pinMode(A0, INPUT); // Switch

pinMode(A6, OUTPUT);






//// SPI Intializations

pinMode(chipSelect_SD_default, OUTPUT);

digitalWrite(chipSelect_SD_default, HIGH);

pinMode(chipSelect_SD, OUTPUT);



digitalWrite(chipSelect_SD, HIGH);

// see if the card is present and can be initialized:

if (!SD.begin(chipSelect_SD)) {

Serial.println("Card failed, or not present");

return;}

Serial.println("card initialized.");

//////////// WEB SERVER

AddHTMLPage(szHTMLSample, ComposeHTMLSamplePage);

AddHTMLPage(szHTMLRestart, ComposeHTMLRestartPage);

AddHTMLPage(szHTMLTerminate, ComposeHTMLTerminatePage);

AddHTMLPage(szHTMLReboot, ComposeHTMLRebootPage);

SetDefaultHTMLPage(ComposeHTMLSDPage);

SDSetup();

ServerSetup();

ProcessServer();

}

void loop()

{

buttoncount();

lcd.setCursor(0,0);



lcd.clear();

// save to file

dataFile = SD.open("target.htm", FILE_WRITE);

dataFile.seek(83);

dataFile.println("");

dataFile.print("var V=");

dataFile.print(vactual,4);

dataFile.print(";");


dataFile.print("var R=");

dataFile.print(R,4);



dataFile.print("var C=");

dataFile.print(C,8);



dataFile.print("var L=");

dataFile.print(L,8);



dataFile.print("var S=");



dataFile.print(count2);



dataFile.close();

switch(count2){

case 0:

lcd.setCursor(0, 0);

lcd.print("Voltage ");

// voltage acquisition

v=((3.25-0)/(pow(2,10)-1))*analogRead(A2);

vactual=-(v-(1+r2/r1)*vref)/(r2/r1);

// print to lcd

lcd.setCursor(0, 1);

lcd.print(vactual);

lcd.print("V");

break;



case 1:

lcd.setCursor(0,0);

lcd.print("Resistance ");

vr=0;

for(int i=0;i



fc=(1/(2*pulseIn(A4, HIGH)*pow(10,-6))) ;

C=1/((rc1+rc2)*fc);

CmF=C*pow(10,3);

CuF=C*pow(10,6);

CnF=C*pow(10,9);

lcd.setCursor(0,1);

lcd.print(CuF, 6);

lcd.print(" uF");

break;

case 3:

lcd.setCursor(0,0);

lcd.print("Inductance ");

fi=(1/(2*pulseIn(A5, HIGH)*pow(10,-6))) ;

w=(2*3.14159265359*fi);

w2=pow(w,2);

L=1/(w2*CT);

LmH=L*1000;

lcd.setCursor(0,1);



lcd.print(L,6);

lcd.print(" H");

break;

}

ProcessServer();

delay(40);

}

void buttoncount(){

x=digitalRead(A0);

if(x==HIGH){

count++;

if(count>10){

count2++;

count=0;

if(count2>3){

count2=0;

}}}}



Code for Webserver

/*********************************************************************/

/* */

/* HTTPServerConfig.h */

/* */

/* The network and WiFi configuration file required */

/* to specify the network parameters to the network libraries */

/* */

/*********************************************************************/

/* Author: Keith Vogel */

/* Copyright 2013, Digilent Inc. */

/**********************************************************************

**/

/*

This library is free software; you can redistribute it and/or

modify it under the terms of the GNU Lesser General Public

License as published by the Free Software Foundation; either

version 2.1 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful,

but WITHOUT ANY WARRANTY; without even the implied warranty of

MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

GNU



Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public

License along with this library; if not, write to the Free Software

Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA

*/

/**********************************************************************

**/

/* Revision History: */

/* 7/19/2013(KeithV): Created */

/**********************************************************************

**/

#if !defined(_WEBSERVERCONFIG_H)

#define_WEBSERVERCONFIG_H

//*********************************************************************

***

//*********************************************************************

***

//****************** SET THESE VALUES FOR YOUR NETWORK

*****************

//*********************************************************************

***



//*********************************************************************

***

// You have a choice of either calculating a static IP based on LocalStaticIP (next varia-

ble)

// Or setting the whole IP yourself. If you want DHCP to supply and automatically set

// your network parameters, set this to {0,0,0,0}. However, you then MUST set lo-

calStaticIP.

// If you fully specify your static IP, then you do NOT need to set localStaticIP

// but you MUST then set the remaining Gateway, subnet, and DNS values below.

//static IPv4 ipMyStatic = {192,168,1,225}; // a place to calculate our static IP

static IPv4 ipMyStatic = {0,0,0,0}; // a place to calculate our static IP

// This will be ignored if ipMyStatic is NOT set to {0,0,0,0}

// If ipMyStatic == {0,0,0,0} AND localStaticIP == 0, then the full IP returned by

DHCP will be used

// Otherwise this is the last octet in the IP address... so if DHCP comes up with a subnet

of 192.168.1.x

// this will set your IP address to 192.168.1.(localStaticIP) for example if

// localStaticIP == 190; your final IP address would be 192.168.1.190 assuming the

subnet address of 192.168.1.x



static byte localStaticIP = 195; // this will be the gateway IP with the last octet of the

IP being 195

// Set the port to listen on; this is a required item

static unsigned short listeningPort = 80; // 80 is the default for an HTTP server

// how many sockets/connections will we be able to handle at once? Also required

#define cMaxSocketsToListen 6

// You ONLY MUST set these if you specifically assigned ipMyStatic to a static

// IP address other than {0,0,0,0}; otherwise DHCP will overwrite these.

static IPv4 ipGateway = {192,168,1,1};

static IPv4 subnetMask = {255,255,255,0};

static IPv4 ipDns1 = {8,8,8,8}; // public Google DNS server

static IPv4 ipDns2 = {8,8,4,4}; // public Google DNS server

//*********************************************************************

***

//*********************************************************************

***

//***************** SET THESE VALUES FOR YOUR WIFI AP

******************

//************* only have to set these if you are using WiFi *************



//*********************************************************************

***

//*********************************************************************

***

#ifdef USING_WIFI

// Specify the SSID of your AP

const char * szSsid = "jabran";

// select ONLY 1 for the security you want, or none for no security

// then updated the appropriate section below for your key or passphrase

#define USE_WPA2_PASSPHRASE

//#define USE_WPA2_KEY

//#define USE_WEP40

//#define USE_WEP104

#define USE_WF_CONFIG_H // See documentaton for WF_Config.x override

// modify the security key to what you have.

#if defined(USE_WPA2_PASSPHRASE)

const char * szPassPhrase ="hello123";

#define WiFiConnectMacro() DWIFIcK::connect(szSsid, szPassPhrase, &status)



#elif defined(USE_WPA2_KEY)

DWIFIcK::WPA2KEY key = { 0x27, 0x2C, 0x89, 0xCC, 0xE9, 0x56, 0x31, 0x1E,

0x3B, 0xAD, 0x79, 0xF7, 0x1D, 0xC4, 0xB9, 0x05,

0x7A, 0x34, 0x4C, 0x3E, 0xB5, 0xFA, 0x38, 0xC2,

0x0F, 0x0A, 0xB0, 0x90, 0xDC, 0x62, 0xAD, 0x58 };

#define WiFiConnectMacro() DWIFIcK::connect(szSsid, key, &status)

#elif defined(USE_WEP40)

const int iWEPKey = 0;

DWIFIcK::WEP40KEY keySet = { 0xBE, 0xC9, 0x58, 0x06, 0x97, // Key 0

0x00, 0x00, 0x00, 0x00, 0x00, // Key 1

0x00, 0x00, 0x00, 0x00, 0x00, // Key 2

0x00, 0x00, 0x00, 0x00, 0x00 }; // Key 3

#define WiFiConnectMacro() DWIFIcK::connect(szSsid, keySet, iWEPKey, &status)

#elif defined(USE_WEP104)

const int iWEPKey = 0;

DWIFIcK::WEP104KEY keySet = { 0x3E, 0xCD, 0x30, 0xB2, 0x55, 0x2D, 0x3C,

0x50, 0x52, 0x71, 0xE8, 0x83, 0x91, // Key 0



0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,

0x00, 0x00, 0x00, // Key 1

0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,

0x00, 0x00, 0x00, // Key 2

0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,

0x00, 0x00, 0x00 }; // Key 3

#define WiFiConnectMacro() DWIFIcK::connect(szSsid, keySet, iWEPKey, &status)

#elif defined(USE_WF_CONFIG_H)

#define WiFiConnectMacro() DWIFIcK::connect(0, &status)

#else // no security - OPEN

#define WiFiConnectMacro() DWIFIcK::connect(szSsid, &status)

#endif

// this should be uncommented if you want to restart

// the WiFi connection when DNETcK is restarted.

// This is generally uninteresting unless you have a reason

// #define RECONNECTWIFI



#endif // USING_WIFI

//*****************************************************************

//*****************************************************************

//******************* END OF CONFIGURATION *********************

//*****************************************************************

//*****************************************************************

#endif // _WEBSERVERCONFIG_H

Code for SD card

/**********************************************************************

**/

/* */

/* HTMLSDPage.cpp */

/* */

/* Renders pages off of the SD card filesystem */

/* Typically you would make this the default page handler */

/* */

/**********************************************************************

**/

/* Author: Keith Vogel */

/* Copyright 2013, Digilent Inc. */



/**********************************************************************

**/

/*

This library is free software; you can redistribute it and/or

modify it under the terms of the GNU Lesser General Public

License as published by the Free Software Foundation; either

version 2.1 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful,

but WITHOUT ANY WARRANTY; without even the implied warranty of

MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

GNU

Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public

License along with this library; if not, write to the Free Software

Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA

*/

/**********************************************************************

**/

/* Revision History: */

/* 7/19/2013(KeithV): Created */



/**********************************************************************

**/

#include

/**********************************************************************

**/

/* SD Card Reader variables */

/**********************************************************************

**/

#define pinSdCs PIN_SDCS

// used externally to this file

// this should not be used externally directly

// use the "is/take/release" functions defined in HTPServer.h

bool fSDfs = false;

uint32_t sdLockCur = SDUNLOCKED;

uint32_t sdLock = 1;

// you can use this directly externally only if you "take" the card reader

File fileSD = File();

static const char * szFileName = NULL;

static const char szDefaultPage[] = "HomePage.htm";



static CLIENTINFO * pClientMutex = NULL;

static uint32_t cbSent = 0;

static uint32_t tStart = 0;

static uint32_t sdLockId = SDUNLOCKED;

/**********************************************************************

**/

/* HTML Strings */

/**********************************************************************

**/

static const char szEndOfURL[] = " HTTP";

static const char szGET[] = "GET /";

/**********************************************************************

**/

/* State machine states */

/**********************************************************************

**/

typedef enum {

PARSEFILENAME,

BUILDHTTP,

EXIT,

SENDFILE,



JMPFILENOTFOUND,

DONE

} STATE;

/*** void SDSetup(void)

*

* Parameters:

* None

*

* Return Values:

* None

*

* Description:

*

* Initializes SD Reader for HTML file operations

*

* ------------------------------------------------------------ */

void SDSetup(void)

{

// set up the lock counters

sdLockCur = SDUNLOCKED;

sdLock = SDUNLOCKED + 1; // never want this to be zero



// Set the pin used to control the SS line on the SD card to output.

digitalWrite(pinSdCs, HIGH);

pinMode(pinSdCs, OUTPUT);

// See if there is an SD card connected

// and that the motion subdirectory exists

fSDfs = false;

if (SD.begin(pinSdCs))

{

// Card successfully initialized, so we have a file system.

Serial.println("SD card initialized. File system found.");

if(SD.exists((char *) szDefaultPage))

{

Serial.print("Default HTML page:");

Serial.print(szDefaultPage);

Serial.println(" exists!");

fSDfs = true;

}

else

{

Serial.print("Unable to find default HTML page:");



Serial.println(szDefaultPage);

}

}

else

{

Serial.println("Unable to find SD Card Reader or filesystem");

}

}

/*** GCMD::ACTION ComposeHTMLSDPage(CLIENTINFO * pClientInfo)

*

* Parameters:

* pClientInfo - the client info representing this connection and web page

*

* Return Values:

* GCMD::ACTION - GCMD::CONTINUE, just return with no outside action

* - GCMD::READ, non-blocking read of input data into the rgbIn buff-

er appended to the end of cbRead

* - GCMD::GETLINE, blocking read until a line of input is read or un-

til the rgbIn buffer is full, always the line starts at the beginnig of the rgbIn

* - GCMD::WRITE, loop writing until all cbWrite bytes are written

from the pbOut buffer



* - GCMD::DONE, we are done processing and the connection can be

closed

*

* Description:

*

* This renders a page off of the SD filesystem. Pages of type

* .htm, .html, .jpeg, .png, .txt and more may be rendered

* The file extension on the filename determine the MIME type

* returned to the client.

*

* ------------------------------------------------------------ */

GCMD::ACTION ComposeHTMLSDPage(CLIENTINFO * pClientInfo)

{

char * pFileNameEnd = NULL;

GCMD::ACTION retCMD = GCMD::CONTINUE;

switch(pClientInfo->htmlState)

{

case HTTPSTART:

if(pClientMutex != NULL || (sdLockId = lockSD()) == SDUNLOCKED)

{



break;

}

pClientMutex = pClientInfo;

Serial.println("Read an HTML page off of the SD card");

Serial.print("Entering Client ID: 0x");

Serial.println((uint32_t) pClientMutex, HEX);

pClientInfo->htmlState = PARSEFILENAME;

retCMD = GCMD::GETLINE;

break;

case PARSEFILENAME:

// the assumption is that the file name will be on the first line of the command

// there is a bunch of other stuff on the line we don't care about, but it is at the

// end of the line.

Serial.println((char *) pClientInfo->rgbIn);

// find the begining of the file name

szFileName = strstr((const char *) pClientInfo->rgbIn, szGET);

if(szFileName == NULL)



{

pClientInfo->htmlState = JMPFILENOTFOUND;

break;

}

szFileName += sizeof(szGET) - 1;

// find the end of the file name

pFileNameEnd = strstr(szFileName, szEndOfURL);

if(pFileNameEnd == NULL)

{


break;

}

else if(pFileNameEnd == szFileName)

{

szFileName = szDefaultPage;

}

else

{

*pFileNameEnd = '\0';

}



Serial.print("SD FileName:");

Serial.println(szFileName);

if(SD.exists((char *) szFileName))

{

Serial.print("HTML page:");

Serial.print(szFileName);

Serial.println(" exists!");

pClientInfo->htmlState = BUILDHTTP;

}

else

{

Serial.print("Unable to find HTML page:");



}

break;

// We need to build the HTTP directive

case BUILDHTTP:

if((fileSD = SD.open(szFileName, FILE_READ)) && fileSD.seek(0) )



{

pClientInfo->cbWrite = BuildHTTPOKStr(false, fileSD.size(), szFileName,

(char *) pClientInfo->rgbOut, sizeof(pClientInfo->rgbOut));

if(pClientInfo->cbWrite > 0)

{

pClientInfo->pbOut = pClientInfo->rgbOut;

retCMD = GCMD::WRITE;

pClientInfo->htmlState = SENDFILE;

cbSent = 0;

tStart = millis();

Serial.print("Writing file:");


}

else

{

Serial.print("Unable to build HTTP directive for file:");



}

}

else

{

Serial.print("Unable to open HTML page:");





}

break;

// Send the file

case SENDFILE:

{

uint32_t cbT = 0;

if((cbT = SDRead(fileSD, pClientInfo->rgbOut, sizeof(pClientInfo-

>rgbOut))) > 0)

{

cbSent += cbT;

pClientInfo->pbOut = pClientInfo->rgbOut;

pClientInfo->cbWrite = cbT;

tStart = millis();

retCMD = GCMD::WRITE;

}

else if(cbSent == fileSD.size())

{

pClientInfo->htmlState = EXIT;

}

else if((millis() - tStart) > SDREADTIMEOUT)

{

A Multi-Measurement Uni

Documents

Multi measurement Unit