I'm working on a circuit to activate a relay with an Arduino, adapted from this schematic:
The relay is a RTE24005, which has a 5V coil. When I use the 5V and ground from the Arduino it works perfectly.
When I use a wall wart power supply instead (5V, 550mA), it fails to switch.
The only real difference I can tell is that the wall wart isn't the same ground as the the input from the Arduino.
Does this make a difference?
Is there something else that I'm missing?