HRV Heart Sensor Lab 2

 

https://pulsesensor.com/pages/micro-bit-fun = Demonstration of Sensor using LED matrix

https://pulsesensor.com/pages/pulsesensor-manual = User guide/Extended Manual

The HRV (Heart Rate Variability) Heart Sensor is used to measure the user’s heartbeat. The sensor measures blood volume changes using photoplethysmography which is a common technique that can also be found in smart watches and medical devices.

The HRV Heart sensor emits a light using an LED. A small portion of this light is absorbed while the rest of the light is reflected. The reflected light changes with respect to the volume of blood during each heartbeat.

A photodiode is used to detect the amount of reflected light. Using code that is created for the Micro:Bit, the signal can be interpreted.

The objective of this lab is to construct the appropriate circuit and code to successfully interpret the outputted signal which can be represented on a graph.

The above circuit (top) and code (bottom) are required to successfully interpret the signal from the HRV Sensor where the sensor is plugged into the P0 pin of the Micro:Bit. Initially, I included a delay of 100 milliseconds. I found this to be a poor decision as it greatly affected the accuracy of the signal being displayed in the graph. After removing the delay, the signal became much clearer and accurate to what is expected of a heartbeat.


The above image illustrates the output from the circuit and code. It can be seen that there are 3 large spikes in the output, this was due to a poor connection from the Micro:Bit to the board that it was mounted to, however, after the connection was adjusted, a clear signal can be seen of my heartbeat.

I found this to be an interesting lab. If I could further develop on this project, I would like to include MQTT to send the heartbeat to another device. This could be expanded on with multiple sensors to monitor a group of heart beats.

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