Homemade ECG Machine: Improving Daily

UPDATE: An improved ECG design was posted in August, 2016.
Check out: http://www.swharden.com/wp/2016-08-08-diy-ecg-with-1-op-amp/

As most of my readers know, I’ve been slowly building a homemade ECG machine over the last month. This is the most basic circuit I’m currently using, designed using two quad op-amps (LM324s). I’ve produced some surprisingly good ECG traces and even identified an arrhythmic heartbeat while I was just sitting watching TV. Currently the device is limited because you have to be attached to your computer, but in the spirit of continuously improving my work I’m working toward making it a modular device (powered by a 9V battery) which dumps heart voltage potential data to a minidisc recorder . There’s one problem – how can I optimally adjust the gain (input power) if I cannot see the trace of the wave on a monitor? I’ll billed a VU meter to monitor the output, of course! My minidisc recorder can take mic-in and echo it the line-out at the same time, so I’ll just put the VU meter on the line-out and it shouldn’t affect my trace. The result is that I can walk around for 24 hours, recording my ECG, with a device I hope to get down to the size of a cell phone. (Maybe a 1990s cell phone?)

Here’s the most attractive (super-simple) LED-based digital VU meter circuit I’ve found, along with some sample images of its (bread-boarded) construction. I have all the parts at home I think, so it should be straightforward to make. The pain now is the electrodes (which are still the junky ones made from scissor-cut aluminum cans), and I think I might splurge and buy some actual disposable ECG electrodes. I think the total cost of my device as it stands is about $4, so I don’t want to spend more than I have to on electrodes.

In other news it appears I’ve been accepted into dental school. I got a voicemail this morning at 8am, another one at 12:30pm, and apparently one on my parents’ answering machine (I listed them as an alternate number). Then they sent me an email! (pictured) They reject me one year, then get all spastic about my acceptance when I re-apply two years later – what gives? Here’s a snapshot from my inbox, and don’t forget The Phone Call 1 and The Phone Call 2!