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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?