The MacGyver way of heart rate logging

Before I begin I have to say that to the best of my knowledge this device is absolutely safe but I cannot guarantee that. Therefore am not liable if you PC explodes, your house burns down or any other unfortunate event results from you trying to recreate it.


So I had this idea that it will be pretty interesting to record my pulse while meditating. Unfortunately, as it often happens, I decided that I have to do this right away and didn't have time to order parts for any device. As a result, I built something from things laying around and it seems to do the trick!

Here is the parts list:

Old PC microphone,
Soda bottle
Candy with plastic wrapper
Super/Crazy glue
matches/lighter

Assembly:

Take the microphone and break it! It should have a small microphone element in it connected to the wire and surrounded by all the unnecessary plastic. Luckily, the microphone that I used was pretty simple to take apart and the wire with mic and plug came out in one piece. The actual mic. is a small (about 1cm) circular element.

Take the cap off the soda bottle. Drill a hole in its top so that the mic element extracted at the previous step will just fit (it has to be tight).

Take the candy and eat it (if you are on a diet- throw it away) but keep the plastic wrapper.
Put super glue at the lower edge of the soda bottle cap. Stretch the wrapper on a table and glue the cap to it (you can trim the extra edges).

Using the matches, heat the plastic wrapper FROM A DISTANCE to stretch the plastic further. If you get it too close, the plastic will melt and you will have to eat more candy and try again.

When the plastic is tight, insert the mic in the hole on top of the cap. The entire cap should be airtight right now and vibrations from the big (candy wrapper) membrane should transmit easily to the microphone.

soda cap
________
||.........|
||.........|
||.........|
mic........| candy wrapper membrane
||.........|
|| ........|
||______|


Use any recording software on the PC to record the signal from the device. Placing the cap on your neck (where you normally measure pulse) and pressing lightly seems to do the trick. I processed the signal using MATLAB (I can post the code if people are interested).

I am including some pictures of the device and the signal that I recorded. As a next step, I amm getting a real data logger and will try to make an optical pulse measuring device. Good luck if you try this and please post comments.