[John Miller] has the perfect response next time he complains about an ache or pain and one of his friends says, “You should listen to your body!” As you can see in the video below, he already does. Using two 9V batteries and some instrumentation amplifiers, [John] built an electromyography (EMG) rig.
If you haven’t heard of EMG, think of EEG or EKG, but for muscles instead of your brain or your heart. The LT1167 amplifier is well-suited for this application and even has a data sheet showing how to create an EMG circuit. [John] also used some more garden-variety op amps and the ubiquitous LM386N chip for audio amplification.
This isn’t the first EMG rig we’ve seen, but [John] does a nice job of explaining why such a special amplifier is used and how it works. He also provides a lot of pointers to more detailed information, including a paper that covers the safety aspects of hooking yourself — or anyone — up to electronics.
The op amps require a dual polarity power supply, so the project uses two 9V batteries. Not only is this handy, but it eliminates any concerns about the device that connects to you getting power from the wall.
Why do you want to listen to muscles? Maybe just to do it, which is a perfectly good excuse around here. However, it is possible to use the signals to control devices like prosthetic limbs, cursors, and more. You can even move someone else’s arm with the right equipment.