I want to drive this relay board with the Imp GPIO.
Are they 5V tolerant? I will supply the 5V to the relay board from another source.
The spec is 3.6v maximum, sorry.
It’s a shame that relay board uses PNP transistors. If it used NPNs you’d be able to drive it with 3.3v no problem. I’ve no idea why they’d use PNPs, that’s just really unusual.
They make another board which looks like it uses an NPN, though there’s no schematic for it: http://www.emartee.com/product/41852/5V%20Relay%20Module
…the fact that their test code says that when they drive the control line high the relay closes implies that it’s an NPN setup (with a PNP setup, you need to drive the line low to turn the relay on).
With the 41852 board you’d power the relay board at 5v, eg from the april VIN line, connect the april and relay board grounds together, then connect an imp pin to the relay control line. Done.
How about this one?
http://www.thesunrain.com/Amazon/2%20relay%20board/2-ch%20relay%20module.pdf
Found here: http://www.amazon.com/SainSmart-2-Channel-Relay-Module-Arduino/dp/B0057OC6D8
Found my own answer I think but please confirm:
That’s a different relay board, and if you get that one then yes, the link you have posted is the correct instruction for use with the imp.
Actually, that SainSmart relay board is really nice. The relay drive is opto-isolated from the control input - unusual but cute.
…just don’t try a similar thing with the emartee part!
Amazon Prime rocks! I should have it Monday!
Which should I use DIGITAL_OUT_OD_PULLUP or DIGITAL_OUT_OD?
What state are these in when the Imp comes up? I don’t want these relays to turn on when it first gets turned on.
The imp pins all come up as inputs with no pull up or down - ie, floating.
As there’s an LED in the optoisolator, you need several milliamps to flow to trigger the relay, ie you need to be pulling the line hard low (floating won’t turn it on).
You can use plain DIGITAL_OUT if you want, as driving hard high will do nothing. Either of the other ones you suggest will work too, as low is the only critical state.