Everyone who has ever designed an electronic circuit knows the anxiety of the first power up of a new prototype. Maybe it's just me, but rarely a newly designed circuit works as expected the first time electrons start flowing through resistors, capacitors and ICs. Thankfully, we have breadboards and perfboards to build and test a prototype before jumping to a PCB design. But even so, after spending hours soldering your new and shiny PCB, having inhaled the fumes of solder, with back pain and eyestrain, because of some kind of mysterious black magic, you power up the circuit, measure its output and... nothing happens. So it begins the process of "debugging" the circuit: checking and rechecking the schematics and PCB design, testing continuity, measuring the output of every stage... If you are lucky, the problem is due to a faulty IC, or for placing the wrong component. But sometimes the problem is worse, and you have made a design mistake in the connection of some components, or the traces are not wide enough to withstand the current flowing through them, or the grounding is badly designed and induces lots of noise on the system, or you forgot to put that 10 pF capacitor in pin 13 of U4 that didn't seem that important...

Of course, the first test of the EMG sensor was no exempt of the "no signal at the output" problem. Thankfully, the problem was solvable, two components were misplaced and the values of two resistors were wrong. So after desoldering and resoldering the problematic components, I powered the circuit again, measured the output and... hurray!!! A nice and clean EMG signal popped out on the oscilloscope screen. The project goes on.