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Wireless Pulse OximeterWireless Pulse OximeterGroup #7
Frank BrunoMatthew EcklundHeather Grenitz
Eric Roberts
Sponsored by:
http://www.betterworldengineering.com
Project DescriptionProject Description
Wireless, remote monitored Pulse Oximeter
Consists of two units◦
TSU: Transmitting Sensor Unit◦
RDU: Receiving Display Unit
TSU will be worn by patient, RDU monitored by caregiver
Finger sensor will obtain data, the TSU will calculate the pulse-ox values and transmit the information to the RDU, where it will be displayed
GoalsGoals
Ultimately to monitor infants at risk of SIDS
Less obtrusive and more easily worn for long periods of time compared to hospital units
More affordable than existing wireless units
Remote monitoring
Ideal for a wide variety of users
Maximum protection at minimal cost
ObjectivesObjectivesTransmitting Sensor Unit (TSU)
Able to be worn on the wrist with an attached finger sensor
Battery powered
Control the Pulse-Oximeter Sensor
Make calculations to achieve accurate Pulse-Ox data
Monitor unit’s battery life
Transmit data wirelessly to the RDU across a midsize home
Receiving Display Unit (RDU)
Receive data wirelessly from the TSU across a midsize home
Display Patient’s Pulse-Ox data
Wall powered with battery backup
Display TSU Battery life and RDU battery status
Audible alerts for critical conditions, loss of signal and low battery
Overall Block DiagramOverall Block Diagram
MCU Sensor
PowerAntenna
Transceiv er
MCU
Display
PowerAntenna Speaker
Status Indicator
s
Transceiv er
Wireless OptionsWireless Options
Transmission Methods◦
Bluetooth◦
Zigbee◦
Custom Radio Frequency and Protocol
Custom RF and protocol chosen◦
Alternatives have high overhead and a large amount of unnecessary features◦
Requires less power◦
Lower cost parts
MicrocontrollerMicrocontroller
Ideally, would use CC430 from Texas Instruments.◦
Composed of MSP430 with internal CC1101
◦
9mm x 9mm QFN◦
32 GPIOs, 12-bit ADC, 2-channel USART
◦
Production has been delayed
Using MSP430F1610 and CC1101 instead◦
12mm x 12mm LQFP, 48 GPIOs and two 12-bit DACs
◦
5mm x 5mm QFN, Sub 1GHz transceiver operating at 915 MHz in the ISM band (FCC 15.247)
◦
Communicate using SPI
TSUTSU
Pulse OximetryPulse Oximetry
Non-invasive optical measurement of heart rate and arterial oxygen saturation of the blood
Hemoglobin is the red colored substance in blood and is the carrier of oxygen
Red and infrared light are attenuated less by body tissues and more by blood (600nm, 940nm)
Light shines through finger and strikes a photodiode, which creates a very small current based on the amount of light incident on the photodiode
Determine attenuation of light based on output of photodiode
TSU SpecificationsTSU Specifications
Sensoro Generate alternating pulses of light at 600nm (red)
and 940nm (Infrared)o Photodiode must detect light in the range of 600nm
to 940 nmo Convert photodiode current to voltage values
between 0V and 2.3Vo Accuracy of 2% (70%-100%, Adult/Pediatric) o 2 BPM for pulse
Transmit a minimum of 100 ft
MCUo Two 12-bit DACso Three 12-bit ADCso 12 GPIOs
Block Diagram TSUBlock Diagram TSU
Red LED SML-LXFT0603SRC-
TR
PhotodiodeOED-SP-23-
TRDiffAmpLT6004
IR LED APT1608F3
C
DC/DCBuck
converterEP5368QI
ADC in
ADC in
ADC in
lightlight
Max 1.5 V
Current VAC + DC
V DC
Trans Amp
LT6004V AC
MCU
ADC
ADC
DAC
LED Control Circuit
V ir V r
IR
R
SensorSensor• To calculate pulse oximetry the photodiode current must be
converted to a voltage
• This voltage has both a DC and AC component that represents
attenuation of light
• DC – constant volume of blood• AC –
ebbing and flowing of blood• AC used for measurements• DC used for AGC
LED1
LED2
PIN1
Photo-Diode
Photo AnodePhoto Cathode
IR_A / RED_CIR_C / RED_A
10 )(
11 111* l
inCC rrooII
10 : )(
22 222* l
inCC rrooII
Automatic Gain ControlAutomatic Gain Control
MCU determines DAC output based on DC component input
Output from the DAC on the MCU controls current to LEDs
To utilize constant DC equation the DC component from red and infrared LED must be the same
AGC constantly monitors output from photodiode and adjusts to maintain the same voltage
R log
1ACI log
2ACI
1122
12
0
02
oror
rr
r RR
CCCSpO
Sensor ControlSensor Control
Control alternating pulses by pair of LED select lines
Common power lines
DAC controls current through system to control
IR_A / RED_CIR_C / RED_A
5k
R14
20R
R15
20R
R16
5k
R17
GND GND
LED_DR1
LED_DR2
DAC DAC
6
2
1
T1A
MMDT2222V-7
3
5
4
T1B
1
2
6
Q2ABC856AS-7
4
5
3
Q2B1kR12 1kR13
+3. 3V
LED_DR1
LED_DR2
1
2
6
Q1ABC856AS-7
4
5
3
Q1B
1kR10 1kR11
LED1
LED2 IR_A / RED_CIR_C / RED_A
RDURDU
RDU SpecificationsRDU Specifications
MCU◦
18 GPIOs◦
One ADC for battery monitoring◦
2 SPI interfaces
Receive from source approximately 100 feet away
Display◦
Minimum 0.4 in◦
Minimum 3 digits◦
Can be seen from 10 ft away
Speaker producing sound at a minimum of a 60dB sound pressure level
RDU Block DiagramsRDU Block Diagrams
4243 digit 7-segmented
DisplayLDT-A512RI
LED Display Driver
MAX6957
LED ArraySSF-LXH400GD
SSA-LXB435SUGD
MCU
4
SPI
Status LEDs
5
SpeakerSMT-0540-T-6-R
SpeakerDrive Circuit
PWM
DisplayDisplay
Must be bright with large numbers to be seen from a distance
3-digit, 7-segment display measuring 1.5in x 0.75in with 0.56in tall digits
Will show heart rate and SpO2 , alternating automatically between the two values
And LED driver, Maxim part number MAX6957, will be used to drive the display, Lumex part numberLDT-A512RI
IndicatorsIndicators
LEDs◦
Orange for signal Lumex part number SSI-RM3091SOD-150
◦
2 Yellow to indicate which measurement is being displayed Chicago Miniature Lighting part number 5100H7
◦
Green 4-LED array for TSU battery life status Lumex part number SSA-LXB425SUGD
◦
Red/Green bicolor LED for RDU backup battery status Dialight part number 558-3001-007F
◦
Blue to show if the AC power is connected Dialight part number 558-0803-007F
◦
All panel mount to the front of the RDU
AlarmsAlarms
Maximize safety by utilizing alarms as well as indicator LEDs
Speaker◦
Audible alerts for:
Danger conditions
Loss of signal
Low power
◦
Surface mount speaker PUI Audio part number SMT-0540-T-6-R
PCB FabricationPCB Fabrication
Using Altium to create schematics and PCB layouts
Need 3 TSU boards and 2 RDU boards for testing and prototyping
Using Sunstone Circuits ValueProtoTM PCB service◦
Specifically for low quantities of small area, two layer boards
◦
Free shipping◦
10-day turn around can be expedited
Estimate the total cost to be approximately $100
Populate boards ourselves
Mechanical DesignMechanical Design
Case sizes are based on PCB and battery dimensions
RDU◦
PCB measures 2in x 2.5in◦
Back up battery pack measures 2in x 2.25in◦
Case measures 6in x 4in x 2in
TSU ◦
PCB measures 0.85in x 2.5in◦
Battery measures 0.70in diameter x 2.65in long◦
Case measures 4in x 2in x 1in◦
Will have wrist strap on the bottom
Example of RDU caseExample of RDU case
Example of TSU caseExample of TSU case
Mechanical DesignMechanical Design
Sensor mechanical design more difficult
Pre-made cases are not available as they are for the TSU and RDU
Several different options◦
Ready-made sensor, with parts replaced◦
Fabric cuff with Velcro or elastic◦
Silicon or alginate mold
Depend on final budget and time to test
SoftwareSoftware
SoftwareSoftware
Efficient and fit inside the parameters of the MCU 5KB RAM and 32KB Flash
The primary language is C with the ability to use assembly if needed
TI Code Composer Studio v4 IDE
Olimex MSP430F1611 Development Board
TSU SoftwareTSU Software
TSU responsible for calculating ◦
SpO2
◦
Heart rate ◦
Battery Life
Communicates data to the CC1101 for RF transmission
Time multiplexed hardware for LED switching
Switch turned onSetup SPI
with CC1101
Setup CC1101 comm
settingsSetup LED
Select Timer
Setup Send and Battery Life Timer
Setup ADCSetup DAC
Calculation Loop
Packet:
MSP430 communicates with CC1101 using SPI
CC1101 notifies MSP430 using interrupts whether a packet has been received or sent successfully
CC1101 library to handle communication between MSP430 and the CC1101
TransmissionTransmission
Receiver Interrupt
Receive Packet from
CC1101
Send Timer Interrupt
Construct and Send
Packet
Header SpO21 Byte
Heart Rate2 Byte CRCBattery Life
1 Byte
Software driven SensorSoftware driven Sensor
Timer Interrupt driven time multiplexing◦
1000 samples per second
Each LED has its current controlled by the DAC
Software driven SensorSoftware driven SensorLED Select
Timer Interrupt
IR LED Selected
Select IR LEDDisable Red LED
Select Red LEDDisable IR LED
Read AC+DC voltage Supply DC Offset to OpAmp
Read in AC only Signal
Digitally process AC signal
Store squared AC Signal and increment Heart
Beat counter
Yes
No
Software RDUSoftware RDU
RDU responsible for receiving calculated data from the CC1101 upon RF reception
Analyze the data ◦
Sound alarms ◦
Changing status indicators
Display alternating between SpO2 and Heart Rate
Switch turned on
Setup SPI with CC1101
Setup CC1101 comm settings
Setup SPI with MAX6957
Setup MAX6957 Ports and Intensity
Setup ADC
Low Power Mode
Setup Timer for Battery Life, Alarm check, and Display
selection
Software driven DisplaySoftware driven Display
SPI communication tells MAX6957 which segments to turn on
LEDs turned on based on status conditions
Display Timer Interrupt
Heart Rate Displayed
Display Heart Rate Select Heart Rate
LEDDisable SpO2 LED
Display SpO2Select SpO2 LED
Disable Heart Rate LED
Yes
No
Software driven SoundSoftware driven Sound
Pulse-Width Modulation (PWM) is required to create sound from a speaker
The software creates a PWM using a timer on the MCU
This process is controlled by software so we can create any sound
Trial and error will be used to determine the correct sounds for the alarm conditions
Timer Interrupt
Alarm Condition
Do nothing
Sound appropriate alarm
Yes
No
Software Battery MonitoringSoftware Battery Monitoring
For the TSU we will drain the battery on a simulated load
Based on this drain we can create a table to lookup the battery life
To determine the battery life several drain tests will need to be performed to understand the battery life of our system. We can choose values to represent 25% increments and change the status whenever the life falls below these values.
Timer Interrupt
Update Battery Life from ADC
PowerPower
Power Specifications Power Specifications –– TSUTSUThe TSU requires a small amount of current at a low voltage for a long
time.
Drain 50 mA or less
Power regulated to be 3.3 V
Run at least 8 hours
Battery Requirement
Working voltage greater than 3.3 V
Charge capacity greater than 400 mAh
Smaller then a C Cell Battery (50mm x 26.2mm)
Rechargeable within 4 hours
Batteries Batteries -- TSUTSULithium Ion Battery Pack w/ Built in safety
3.7 V with 940 mAh
Safeties include 4.2 V Overvoltage Protection, 2.5 V Undervoltage Protections and 3 A Overcurrent Protection
Dimensions: 17 mm in diameter by 67 mm in length
Weighs 27g (0.95 oz)
Estimated Charge Life:Est. drain of 50 mACharge life = 940 mAh / 50 mA = 18.8 hours
Charger
Smart Charger (0.5A) for 3.7V Li-ion/Polymer Rechargeable Battery Packs
4.2 VDC at 0.5 A
Charge time = (.94 Ah x 1.5) / (0.5 A) = 2.82 hours
Power Specifications Power Specifications –– RDURDUThe RDU requires a larger amount of current at a low voltage for a long
time.
Estimated draw of 150 mA
Power regulated to 3.3 V
Run at least 8 hours
Primary power from external 120V AC/DC supply
External AC/DC supply
COTS equipment
5 V DC supplied and rated for 1 A
Battery Requirement
Working voltage greater than 3.3 V
Charge capacity greater than 1200 mAh
Batteries Batteries -- RDURDUThe battery backup will only be used for moving the unit
between rooms or if the power goes out. Thus it will need to be able to power the unit for at least one entire use before draining the battery completely. It will consist of 3x AA Batteries arranged in series in a side-by-side battery holder that will be accessible to the user.
AA Battery◦
1.5V and 2700 mAh◦
14mm in diameter by 50.5mm in length
RDU battery pack◦
4.5V and 2700 mAh◦
2in x 2.25in x 0.75in
Battery MonitoringBattery MonitoringThe battery will connect to a voltage divider, Op Amp, and an ADC input
of the MCUMax Voltage at ADC of MCU: 2.3 VMax Voltage of TSU Battery: 4.2 VMax Voltage of RDU Battery: 4.5 VRatio = 4.2 V / 2.3 V = 1.8264.2 V * (100k / 186.6k) = 2.25 V4.5 V * (100k / 200k) = 2.25 V(Values chosen to account for resistor tolerances)
This voltage will be fed back to the output of the operation amplifier so that the voltage and current coming out of the operational amplifier are acceptable for the ADC input on the MCU
GND
BATT Life
GND
GND100kR3
86.6kR2
+3.3V_ANA
OUT 1-IN2
+IN3
V+
4V
-13
NC8
NC9
S17
U3A
BATT_SW
Automatic Power SwitchAutomatic Power SwitchSince the RDU will have an internal backup battery the system
will need to be able to switch to it automatically when needed.Intersil ICL7673
Automatic Battery Back-up Switch
Connects output to whichever input is greater
Can be adapted to use a rechargeable battery
External Transistors used to increase output currentfrom 38mA to 200mA
6mm x 5mm SOIC
Vo 1
Vs2
SBAR 3
GN
D4
NC5
PBAR 6
NC7
Vp8U2 Auto Power Switch
GND
10uF
C1
GND
GND
VIN
BATT
10uF
C6
Vsw
11
22
33
SW1
LED1
GND
1kR1
1
2
6
Q1AMMDT4126
4
5
3Q1B
154R
R51.24kR4
316R
R31.24kR2
DC/DC ConversionDC/DC Conversion
+3.3V
GND
4.7uF
C9
GND
GND
10uF
C10
GND
EP5368QI
NC 1
PGN
D2
NC 3VFB 4
VSENSE 5
AG
ND
6
VOUT 7
VOUT 8
NC 9
VS010 VS111 VS212
ENABLE13
VIN14
NC 15NC 16
U3Buck Converter
10uF
C11
10000pF
C12
Vsw
Enpirion EP5368QI
600 mA Synchronous Buck Regulator
Voltage is set to 3.3 V
Minimal external components needed
Input is stabilized by the 4.7 uF capacitor
Ripple performance is improved by the 10 uF capacitors
Ideal for space limited RF designs
3mm x 3mm QFN
TestingTestingThere are four major systems that we need to test for our project:
Sensor Functionality◦
Data processed is in a legitimate range◦
Medical Comparison to Hospital-Use Pulse-Oximeters
Successful Transmission◦
The TSU sending the correct information◦
The RDU receiving the correct information
Accurate Display◦
The RDU displays the correct information on the display◦
The RDU makes the necessary updates to all of the status indicators◦
The RDU creates the necessary audible alerts when required
Power Usage◦
TSU runs for at least 8 hours on its battery◦
RDU successfully switches to its battery when unplugged◦
RDU runs for at least 8 hours on its battery
AdministrativeAdministrative ContentContent
BudgetBudgetTSUIC's $28.66
Passive $6.86Transistor $1.16
Other $3.94Price per TSU $40.62
3 TSUs $121.85Cost/TSU after samples $17.59
3 TSUs including samples $52.77
RDUIC's $37.33
Passive $17.81Transistor $0.00
Other $15.36Price per RDU $70.50
2 RDUs $141.00Cost/RDU after samples $46.78
2 RDUs including samples $93.56
Parts $262.86PCBs $100.00DEV boards $45.00Battery $11.00Battery Charger $11.00Total $429.86
Parts including samples $146.33PCBs $100.00DEV boards $45.00Battery $11.00Battery Charger $11.00Total including samples $313.33
MilestoneMilestone ss
Project ProgressProject Progress
Questions?Questions?