oh well, i actually messed with this:
and of course there are cheaper 'knock offs' from here:
https://www.ebay.com/sch/i.html?_from=R ... 32&_sop=15
(think the 'cheap' ones may not be as safe it's good to measure the resistances of the smd resistors and measure voltages, currents esp the probes)
that design supposedly does 'right leg drive' with an intent of removing common mode noise, i'd guess part of that may be that 50/60 hz hum
but simply sitting near an ac source e.g. a switch mode usb charger, pc, etc is adequate to induce visible 50/60 hz noise mixing up with ECG signals (1mv average) the sparkfun's breakout actually use the ad8232 for a low pass filter set at 40 hz cutoff, nevertheless hum is visible.
then i simply have do a software FIR filter to remove the rest of that hum.
my thoughts are that different resistances from the lead wires is sufficient to cause differences that they couldn't be simply removed as 'common mode noise'
an oh btw that sparkfun ad8232 breakout is pretty good as an analog front end for ecg paired with MM/BP
http://www.analog.com/en/products/appli ... d8232.html
it removes a dc bias common in ecg meaaurements, removes baseline drift to an extent and centers the ecg around 1.5v out of 3v, amplifies that 1100 times based on sparkfun's breakout and analog's sample design,
then use an op amp in there to do an analog 40 hz cutoff low pass filter
that output can be simply plotted on an ili9341 with hardly any additional processing
that result is somewhat like this
but interfacing is a lot simplified with the ad8232 breakout, it is simply analogread and just plot that
however, i noted various artefacts which seem to be caused by the ad8232 itself, sometimes there are periodic spikes which i'm not too certain if it is introduced by the ad8232 or true ecg signals
just 2 c