Wiring relays

[murphy]

I am attempting to trigger a store bought animatronic prop using a relay. The prop runs off of a 6V wall wort, and can be triggered with a matswitch. My plan is to trigger the prop through the  matswitch input with a relay controlled by the Prop1.

I have a 5VDC relay I purchased from Radio Shack and would like to trigger it from one of the 3 pin headers. Which 2 of the 3 pins should I connect the relay to? Or am I misunderstanding the purpose of the 3 pin headers?

I have the Prop1 trainer, and have been able to control the LEDs, but can't get the relay to function the way I want.

[JonnyMac]

Do not connect a relay to the 3-pin headers -- even if that relay says it will operate at 5v it probably requires more current than a pin can handle.  Worse, when a release disengages and the magnetic field in the coil collapses there is an induced "kickback" current that can damage the onboard processor.

Rule: Anything with a coil should be connected to the OUTx terminals.  The ULN2803 provides a buffer so that the small signal from the processor can switch a large load, and it also provided protection from kickback currents.

[JackMan]

murphy,
         You can energize your 5v relay using the 6v wall wart that is powering your prop. Connect the positive lead of the wall wart, (you may need to splice it) to one side of the relay coil and the other side of the coil to whatever OUTx you have programmed on your Prop-1. Connect a common ground (-) between the Prop-1 (GND) and the negative side of the 6v wall wart. The N.O. contacts of the relay would take the place of the mat switch. An extra volt to the 5v relay won't hurt a thing.  ;)

[JonnyMac]

A 6v supply may not work with the regulator on the Prop-1, though.  It's an LDO (low drop-out), but really wants 2v of headroom to properly regulate.

[JackMan]

Just so we're all on the same page, use the normal 12v power supply for powering the Prop-1, use the 6v wall wart for your prop and the 5v relay as I outlined above. Of coarse you could also exchange the 5v relay for a small 12v and just connect it to V+ and OUTx on the Prop-1 but RS is usually more trouble than they're worth when returning an item.  8)

[murphy]

I went and bought a 12V relay to use. It seemed the simplest thing to do for my (lack of) skill level! :D And I plan on working this into a scene with some lights, fog and an opening casket triggered by an IR beam.
It worked like a charm, although I did need to wire the relay to normally closed. Otherwise the prop didn't activate until after the relay closed then opened again. ???
Thanks for the help guys!!

[JackMan]

Hmmm....Seems odd, a mat switch is typically a N.O. device. Anyway, glad you got it working.  ;)