If driving three of these boards with the inverted logic, would the arduino current draw be too much to set 24 pins high so as to have the relays 'off'?
I'm using this setup and all my relays are 'on' at startup due to there being no 'high' set.
The relays are powered separately. No current draw on the arduino outputs at this point due to 'low' output states but I would prefer to have the relays off and wonder if driving all 24 outputs high at start-up would be too much.
1) Inverted logic means that when the pin is 'HIGH', no current is flowing.
2) Try writing a 'HIGH' to the pin BEFORE you make the pin an output.
3) A 'LOW' output will SINK ~2mA opto LED current. So 24 relay inputs = ~48mA. Not a big problem.
Current flows from Arduino's 5volt pin, to the relay board's VCC pin, through the opto LEDs and indicator LEDs, back to the Arduino output pins. The Arduino pin switches internally to ground (sinking).