Hi,Show us the exact relay you have (point to data sheet?)..
Sounds like you want an alternating relay, I've used them in industrial work but don't know if they are made in low voltage types. When powered current went to terminal "A", at the same time a solenoid was pulled in, when power was turned off, the sol dropped out, switching to terminal "B". Next on cycle sent current to terminal "B" and so on. Contacts are switched on the falling edge of power input.
The output is tri-state, so it can be HIGH, LOW, or HI impedance. Of course you would need a few components on the other end to translate this to and drive the relay. I think you have the additional obstacle of 70ft of wire to handle as well. That's a long way. Perhaps a drawing of the proposed wiring would be good
Use CAT5 cable for the low voltage, plus a mains cable. That gives you plenty of options, CAT5 ischeap and its resistance properties are well defined - you can common-up multiple wires for morecurrent handling.Otherwise your only option is adding smarts at the relay end (another Arduino) and talk serialto it.
Even if you don't care about the state, you will want to be sure that when you send a signal it switches the relay off or on, regardless of what state it is in.Relays may switch off for whatever reason (short power interruption), so when you think you switch it off, you switch it on. Asking for trouble.Power supply: why not a small 5V adapter at the relay? You have mains power available. Just make sure you connect the live wire before the relay to that adapter. Then you need only two wires to control the relay, no need to string a power supply as well.For the switching, indeed use the three-state ability of the poles. Don't skimp on signals, use 10 mA or so, and require at least 5 mA for it to even react. That makes your setup much more robust - that long wire is an antenna, picking up lots of noise.Make it so that a HIGH signal switches on the relay, and a LOW signal switches it off. As you have a latching relay, a pulse of 0.1-1 seconds or so will do just fine, after which you can set your pin to INPUT and have it not supply any current. Depending on the relay all you probably need is two diodes on the other end to separate these signals.
If you used a SPCO relay you can achieve this by using the traditional 2-switch control of a staircase light. Nothing fancy required.Allan
You may be powering the relay separately, just realize that the signal needs a ground, so....
Yah CAT5 is definately my wire of choice here .
I'll have ground from the main line.