The Heartbeat Huggable

As part of a final project for a sensors class, I developed a simple heartbeat sensor system that was to be implemented in a simulated version of the Huggable Project.

The idea here was someone could hold the hands of the Huggable, and visually be able to see their “pulse”. For this simplistic version, I wanted to feed the ECG signal into an LED “heart” whose intensity would match the ECG waveform. To do this, I needed to create a 2-lead system, one for each hand. After many failed attempts with other circuits, I decided to try a revision of Vadim Gerasimov’s simple ECG circuit, used in the VitaMon project by Michael Sung. In addition to the Sung schematic, I tacked on a second order Butterworth low-pass filter to clean up the signal. Since most relevant ECG data is found well below 40Hz, I set my cutoff to be about 26Hz.

The whole circuit is powered by a 4.8V battery, and the leads are very simple - two pennies. The results were surprising for how simple the circuit was. Although there was a lot of noise that caused the LED to flicker with no contact to the leads, one could actually see the pulse of the LED match the heartbeat once the leads were firmly grasped. In a future revision of this circuit, capacitive sensing would be implemented to detect whether or not the leads are being grasped, so that way, the LED would only reflect the pulse of the heart. Some fine tuning of the low-pass filters could also produce a cleaner waveform that could ultimately be probed and extracted as serial data, so that the waveform could be analyzed with MATLAB or some other program.

The full report of this project can be found below.