I saw the Open Hardware Pulse Sensor at thought I'd try to make it at home. Took me awhile, but here's my bumbling process.
I've been working on re-making the the Open Hardware Pulse Sensor so it'd be "easy" to send off to OSHPark and make at home. I'm not sure but I think I started this project in March (2013) and I've just now finished it.
The bit of encouragement I needed was when hackaday.com put it up as their "Fail of the Week." I thought I was going to be mature about it. But those four red letters started eating at me, so I gave it another go. Weirdly, I got it working.
I do want to take a moment and thank hackaday.com. I know not everyone is happy with them right now, but I firmly believe in their "Fail of the Week" article. It seems like we are all quick to cover projects that work, but that mentality leaves many committing the same mistakes over and over, without realizing there are thousands making that same mistake themselves. Excellent foresight and innovation, hackaday.com. Hats off.
Back to it, I believe there were three problems:
1. I had mixed up the op-amps again. In my defense, I've got 5 different ICs flying about in the same package as the op-amp.
2. The Arduino I'd been plugging into was sitting on a surface that provided enough conductivity to create noise between the 3.3v pin on the underside and A0, which I was using for the op-amp in.
3. Every time I touched the sensor the exposed vias were shorted through my own conductivity. Stupid mineral water.
Anyway, after finishing it and getting it to work, I thought I'd share what information I had gathered.
Here's a video I put together about the fail and problem fixing.