Greetings, all:
I'm working on a project that requires 4 relays be switched from a single Arduino pin. Why a single pin? The project is an audio device which contains several selectable circuits routed to and from a single stereo set of I/O. There are 10 circuits in the chassis, each of which requires 4 relays to fully switch in and out. I would like to use only 10 pins for this part of the circuit (MOST of the rest of the pins are in use for other tasks - RGB display, LEDs, etc.).
I'm using a MEGA, which can supply, what, 40mA per pin @ 5V? The relays I'm using are the lowest current draw for 5V available, but each relay coil still draws 20mA. What's the most efficient (i.e. lowest parts-count) way of keeping 5V steady but amplifying current from the available 40mA per pin up to 80mA?
I was thinking a simple, single transistor emitter follower powered by the 9V utility rail inside the chassis (the same rail that will be powering the Arduino) would do, as long as the small loss in voltage isn't enough to keep the relays from switching.
Anyone have any thoughts on the matter?
Best,
Ian