3102 ECG ProjectGroup 2: Abdiqani Sidow, Alex Motley,

Lucas Knutson, Tim Dirks

Project Overview

● Create an Electrocardiogram (ECG) to output heartbeat waveform to external Oscilloscope

● Display pulse on integrated LCD display

Design Specifications● Max Power: 1 Watt● Signal input voltage: 1mV● Signal output voltage 1V● Power rails: ± 3.0 volts● Minimum Heart Rate: 10 beats/minute● Maximum Heart Rate: 400 beats/minute

System Block Diagram

Analog Filtering Subsystem

● Remove DC offset Voltages● Remove signals above 100 Hz● Notch out 60 Hz ambient noise

Analog Filtering SubsystemParts Chosen

● AD620 Instrumentation Amplifier○ High Precision○ Low Power○ Cost Effective

● TL084 Op Amp○ 4 Op-Amp Chip for simplified routing○ Low Power○ Low DC offset current

Analog Filtering Subsystem

60 Hz Notch

Analog Filtering Subsystem

100 Hz Low Pass

Analog Filtering Subsystem

0.01 Hz High Pass

Analog Filtering Subsystem

Analog Amplification Subsystem

● Gain of 1000 of signal from 1mV to 1 V○ 2 Stages

● Feedback to leg to stabilize the signal from common signal.

Analog Amplification Subsystem

7x gain

Analog Amplification Subsystem

143x gain

7*143=1001

Analog Amplification Subsystem

Feedback Network

Analog Amplification Subsystem

Analog Amplification Subsystem

Analog Amplification Subsystem

● Benchtop testing of amplification showed an output of 1.2 Volts with a 1 mV input sinusoidal input.

● Benchtop testing of feedback circuit still under way

Power Subsystem

● Two CR2450 batteries in series, one providing -3 rail, the other +3 rail, and between them ground

● Solder points on circuit between -3 battery and the point considered to be the -3 rail, same for +3 battery, will allow us to turn the whole circuit on and off with a physical switch

Power Subsystem Circuit Diagram

Power Subsystem

P = I * V 1.7 mA * 6 V = 10 mW

Digital Subsystem

● Specifications:○ Max Power: 0.5 W○ Analog System Input: 1 V○ Max Heart Rate: 400 beats/minute○ Min Heart Rate: 10 beats/minute○ At most last 30 heartbeats used to calculate pulse○ At least 3 heartbeats used to calculate pulse

Digital Subsystem Circuit Diagram

Digital Subsystem Operation

● Analog signal input to comparator on microcontroller, which records time after receiving each heartbeat’s positive and negative components

● Heartbeat times are stored in a circular buffer and a running average is computed

● Running average is outputted to LCD display via LCD driver

Digital Subsystem Status● LCD display hardware and associated code is functional● Hardware for pulse sampling has been ironed out, code is

still in progress○ Incomplete code will not affect PCB design

● Currently not operational, we accidentally fried the LCD Driver○ New LCD driver is on order

● Consumes ~20mW when operating○ This number will go down as we refine the code to put the

microcontroller into a low current state for the majority of its operation

System Integration● Integration has not been done yet

○ Made last minute changes to display type (LCD instead of LED)

○ Analog troubleshooting● Full system integration is planned for the next week

○ At this point, all of the subsystems should be fully operational

○ Biggest problem area will be analog to digital interface, however, room for adjustment exists in the malleability of the code that the microcontroller is running

Final Project Implementation Status

● PCB design will be completed this week○ Majority of Altium work has been completed

● Design work for the enclosure and human interface will start this week

Schedule

BudgetItem Name Quantity Total Price

Digital Subsystem

Pic MicroController 1 $2.32

PIC Chip Holder 1 $0.26

LCD Display 1 $4.41

LCD Driver 1 $4.00

Resistors/Capacitors as needed $1.00

Subsystem Total: $11.99

Analog Amplification Subsystem

Instrumentation Amplifier 1 $8.38

Resistors/Capacitors as needed $2.50

Subsystem Total: $10.88

Item Name Quantity Total Price

Analog Filter Subsystem

4 Op-Amp Chip 2 $1.36

Resistors/Capacitors as needed $2.50

Subsystem Total: $3.86

Overall

Box $15.00

Power/Reset Button $5.00

Battery/Snap Lead Kit $6.77

Subsystem Total: $26.77

TOTAL: $53.50

Conclusions

● Analog system is simulating expected results● Digital System is outputting display● Sufficient progress has been made on the

subsystems to submit PCB files by deadline

Unresolved Problems● Finding a power switch capable of opening/closing two

circuits simultaneously with one flip of the switch○ We will have to find one on digikey (we know that

they exist)● LCD visibility on outside of box while mounted to PCB

○ We will bring the LCD as close to the outside of the box as possible and if necessary add a recessed look

Hardware Demo

● There is high probability that the hardware demo will be successful

● Currently on schedule, which includes time for anticipated problems, such as final integration, and also time for unanticipated problems or necessary PCB changes.

Questions?