A friend has asked me to look into the possibility of constructing a one-off Arduino-compatable 8 channel muscle/EMG sensor for experimentation purposes, and gave the documentation of the commercial (single channel) product available here:
as a spec for the type of device he would like. The product's design seems to be released under a fairly permissive license, so one could theoretically whip up an 8 channel version and distribute it as one wished with no problem.
The design as it stands has some problems, the most obvious of which is that it does not make any attempt to meet any requirements for medical equipment, or provide any form of isolation between the body and the power/ground lines of the host computer's USB port.
A purpose-built piece of equipment would use an isolated supply for everything and run the USB lines to the host through an optoisolator, but because the device is supposed to be used with an Arduino, which uses the USB ground as reference ground for signals coming in to its A/D converters, this makes proper isolation of the body connections somewhat more difficult.
To provide isolation, my thought was to use a pair of 4 channel optocouplers to couple the EMG signal from the input instrumentation amplifiers into the rest of the circuitry. Since the current requirements of the input amps are pretty low, their supplies could be isolated by using an "optoisolator power supply," maybe as simple as some photodiodes charging up capacitors. The instrumentation amp IC used here can run with as low as +/- 1.35 volt rails. Does anyone make4 channel transistor optocouplers with the base terminals brought out, so they could also be used as photodiodes?
Please bear in mind that I realize medical standards are stringent, and I probably do not have the means to test whether a device so constructed adheres to all such requirements. I simply wish to provided an added level of protection for someone who is aware of the risks involved with such experimentation, however small. I myself do not intend to mass-produce the device or make it available for sale.