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?