5. Analog Filtering Subsystem
● Remove DC offset Voltages
● Remove signals above 100 Hz
● Notch out 60 Hz ambient noise
6. Analog Filtering Subsystem
Parts 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
17. 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
18. 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
21. 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
23. 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
24. 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
25. 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
26. 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
28. Budget
Item 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
29. 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
30. 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
31. 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.
