Ok, so here's a real challenge for you gurus! ;)
Could anyone of you come up with a myoelectric sensor? One of those things that pick up the increased voltage across the skin when an underlying muscle contracts.
Myoelectric signals are detected by placing three electrodes on the skin. Two electrodes are positioned so there is a voltage between them when a myoelectric signal occurs. The third electrode is placed in a neutral area, and its output is used to cancel the noise that can otherwise interfere with the signals from the other two electrodes. The output voltage is processed using a device called a differential amplifier. The output of this amplifier has much higher voltage than the myoelectric signals themselves. This higher voltage, which produces significant current, can be used to control electromechanical or electronic devices.
This type of sensors are used in many prostetic devices, but as far as I know (not beeing an amputee myself), a lower-arm myoelectric prostetic device with only gripping-motion (and no feedback from the arm, so you can't, say, pick up an egg) will run you about $5.000! I find this to be rather horrible, seeing as how the guys in the first YouTube video listed below did it with hobbyist gear and a low-end microcontroller.
Now I don't claim to be an expert (nor anywhere close to one), but by using a voltmeter on your skin you'll get a reading within the range of (I think) >0 to 50-60 mV. With amplification and perhaps some noise-smoothing one could at least make this a really neat experiment! 8-) Has any of you expertly people got any experience using "differential amplifiers"? I have never even used an opamp myself so... :-[