So I got two of the infamous 16ch relay boards which don't seem to have a proper isolation between the control part and the switching part (https://www.berrybase.ch/raspberry-pi-co/sensoren-module/relaiskarten/16-kanal-relais-modul). No schematics either, of course. They do have a 5V separate power connector for the coils but the resistance between the 5V/ground pins on the control pins and the power pins is about 1kOhm and current seems to flow through the control pins into the Arduino. At least the LEDs on the arduino are on even if it's not connected to a power supply otherwise.
- Does anyone know a 16ch relay board with proper isolation? Ideally with 5V coil voltage.
- Is it possible to power the Arduino and the relay with two different power supplies in order to reduce EMI going into Arduino's power supply network? I'm getting random USB errors on a Raspi connected to the same power supply as the Arduino and the relay board always correlated with a relay switch.
- Which of the control pins do I actually need to connect with the Arduino. The individual relay pins for sure, but what about GND and 5V? Is it sufficient to only connect one of them? Otherwise the separate power supply for the relay board would still feed into the Arduino, wouldn't it?