/diy/ - Do It Yourself

>>2701927
Vin will only accept voltages above ~6-7V, because it's a 5V linear regulator. The smarter method would be to just connect them directly to the 5V pin, assuming the NiCd cells will clamp the voltage to no more than 5.5V. Could drop to 2xPV 3xNiCd if it isn't clamped, or just use a clamping zener. An Arduino Nano can run on a Vcc of anywhere from 2.7V to 5.5V, though at a lower voltage I doubt the CH340 will act properly, and you may need to turn down the clock frequency in the fuses. I'd also desolder the power LED or its resistor, it burns like 2.5mA constantly so it's bad for battery powered projects where you're making the MCU sleep.