NOTE: If you try this at home, PLEASE don't electrocute yourself!

I recently began designing a prototype ECG for mobile applications. My design goals for this project were mostly educational: to better familiarize myself with the facets of bluetooth connectivity and Android app development.

Analog Design:

The first prototype circuit is fairly ugly -- an INA212 (instrumentation amplifier from Texas Instruments) and two LM741 op-amps were used to amplify and bandpass filter the cardiac signal. The op-amps used here are a second order salen-key design -- making a bandpass filter with lower and upper cutoff frequencies around 1/4 Hz and 150 Hz, respectively. The INA inputs were extracted from sticky chest electrodes. I found a pack of 100 Vermed SilveRest electrodes for under 20 dollars on Amazon. They have an adhesive Ag/AgCl gel on one side, designed specifically for physiological signal acquisition. For a more detailed explanation of the circuit diagram, see "Meditating on Matlab."