For a work project I need to control 2 industrial winches - both remotely (over RS232) and from a pendant. The relays need to be ~30 Amp and 120VAC (we stock those at work). For bidirectional control I need 4 relays.
I need to monitor limit switches and user buttons.
I already have microcontrollers in hand (3.3V ARM).
I did a quick Google search and I didn’t see anything exactly like I need. I’ll be designing my own circuit for this project (for schedule’s sake), so this isn’t a question of how-to. But I figured I couldn’t be the only person wanting to use their own relays with a microcontroller.
If I use sparkfun parts, I’ll use the photocouplers to provide isolation to and from the ARM (separate packs for each direction powered from the proper sides, of course) = (http://www.sparkfun.com/commerce/produc … cts_id=784)
Then I’d use the multi-darlington pack to drive the relays (http://www.sparkfun.com/commerce/produc … cts_id=312).
The parts are cheap enough. And I’ve seen many people that don’t have much electronics experience ask this question on the Sparkfun forums (and other furms).
Is this too “industrial” for sparkfun?
-Matt
I’ve used the darlington transistor arrays to drive relays (12V or 24V coils) from a MCU, as long as the ULN2803 pin 10 is connected to the relay psu. Pretty much the same circuit as the Rabbit SE1100 relay board but I wouldn’t use the output optos, the relays already provide isolation, see schematic: http://www.rabbit.com/products/se1100/docs.shtml
For digital inputs, I use opto-couplers like the PS-2501 with extra LED’s so I know what’s on and off.
Don’t put the relays close to the CPU, as the contacts usually arc which makes too much EMI/RFI and things will crash.
If the winches can hurt anyone during a malfunction (code error, relay gets stuck etc.), you need emergency stop buttons that override the whole thing.
I did a commercial project like this but used garage door opener RF kits and some logic.
Yes, well aware of the E-stop button.
Also that board from Rabbit looks great - EXCEPT the relays aren’t big enough. But I think I’ll get a couple of them, remove the relays, run coil power to the output terminals, and run to my larger relays from there.
That’s certainly MUCH cheaper and quicker than me rolling my own board.
Notice that Rabbit also provides optically isolated inputs.
-Matt