2016-03-13 (Su) Cyborg Heart Rate Sensor

When the feedback device, like a motor or coil, and the sensor were taking power from the same voltage regulator it was not surprising to see the light on the sensor fluctuate. This fluctuation lead to the contaminated readings before. To keep this from happening the feedback device and sensor must be separated. The inductor coils wound for this project were not fragile nor would they be harmed by more than five volts so they would be run by a regular battery. A 9V battery in this case. Since the sensor required a steady voltage and current it would be powered by the on-board voltage regulator. A USB battery pack couldn't be used because they also have a voltage regulator inside. Alternatively a large voltage regulator and battery could be used but it would have to be large enough to supply the peak current of the coil and that would not be a convenient package.

A graph was sketched of the effects of keeping the feedback device, red, and the sensor, green, on the same low-current supply. The bottom graph showed what it might look like if the two were separated. Depending on how much current the battery could supply there could still be fluctuation but it should be reduced.

Comparison of combined VS separated circuits

Another sketch was made, very similar to first transistor circuit, which showed a 9V battery supplying power to the controller, with on-board regulator, and the coil, powered directly from the battery. The sensor was not shown but it would be powered solely by the controller board. A 9V battery wouldn't be a suitable choice to combine with a vibrator motor, which expects 3.3V. It would be possible, and easy, to supply 4.5V from three single cells, which would probably be enough to power the controller and sensor.

Circuit with separation

The circuit was constructed and a program was loaded to oscillate the transistor-coil and simultaneously blink the LED at full power. The duty cycle on the coil was approximately 10%. This didn't work and the cause was unknown when this blog was written. Interestingly, the coil would activate when the controller was supplied by USB power.

LED blinking but coil inactive

To do:
  • Record set of analog input data showing heart sensor readings. 2mS readings
  • Rerecord at same location with vibrator motor activating periodically and observe any discrepancies in signal due to motor use
  • If the motor activation causes a problem the project may not work without a second voltage regulator
  • If there is no problem
    • Take second reading at different body location
    • Take third reading at different body location
    • Compare data
    • Write pseudo code for extracting heart rate
    • Program with Arduino UNO

The rest of the posts for this project have been arranged by date.

First time here?

Completed projects from year 1.
Completed projects from year 2

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2016-03-09 (W)