I bought a PS2 to Saturn controller adapter, and now have trimmed down the circuitry of a wireless PS2 pad so it fits into a model 1 Saturn pad. In theory, I can run wires from ground to ground, then between each pad’s buttons so it simulates an “OEM” RF wireless controller 🙂

One problem though, I want to put a rechargeable battery inside that can be recharged via micro USB or whatever. Adafruit has some good products, but the batteries seem to be mostly 3.7v. The wireless pad is generally run on 2 AA batteries which only give 3v correct? More confusing, I think I read that 3.7v batteries are 4.2v when fully charged?? Can I just buy a “3.7v” battery and cut down the voltage with a simple resistor?

I feel like this is a really simple problem but can’t find an immediate solution myself it seems…thanks for any help!

A resistor won’t work, because the voltage will change as the battery depletes (which you alluded to, already). You should use an LDO (low drop-out) voltage regulator. One popular example would be the LM1117. It’s an adjustable regulator, which means you can set the output voltage using a resistor (which is explained in the datasheet, along with other support components you’ll need, such as filtering capacitors). I just bought something that contains three of the little guys! (presumably all set to different voltages).

For the highest efficiency, you could even use a switching regulator, but for one this size, the cost will likely outweigh the benefit (and if you cheap out on it, the efficiency will likely be worse than the LM1117).