I have a wall mounted reverse-cycle controller but no wireless remote. The push-buttons on the controller are basically like membrane switches - they just complete a particular circuit on the controller PCB when pressed.
I'm going to solder two wires on to the controller PCB at points that are common to each side of the on/off switch. If I want to control this switch with an Arduino, is a relay the only practical option?
I read another post that suggests a transistor could be used as a switch. To do this would I need to know more about the voltages/current through the controller PCB switch circuit?
You don't want line voltages and Arduino voltages mixing. Relays give perfect isolation and are not normally an issue. You can use low bounce "mercury wetted" reed relays since current shouldn't be an issue.
The hazard is that you get an ohmic connection of the Arduino to the line and then touching the Arduino and ground at the same time can lead to shock hazard.
Assuming it actually uses 5 V logic, a 74HC4066 would do the job nicely. It will require the Arduino/ ESP to have a common negative with the logic on the board, and even run off the same power which is presumably 24 V AC.
But you need to know on what voltages it operates.
Thanks, I'll poke around the controller board a little more. I'll look around online some more in case there are some specs available (though I doubt it).
It's a Toshiba controller powered by two wires which also carry an ancient serial protocol. There have been some attempts to decipher the protocol, but nothing complete yet, so I gave up on that approach and figured I'll just operate the power button and maybe temperature up/down buttons remotely instead.
Many years ago, I had to interface an X-10 Power Line Controller to a microprocessor based piece of equipment. The PLC had 16 buttons so I used 16 4N26 opto-couplers connected across the existing buttons. It was clunky and not very elegant, but it worked exactly the way I needed. The LED side of the optos were connected to 2 ports on a peripheral chip and they provided the necessary isolation !!
A relay is the safest and most foolproof solution if you don't know exactly how the circuit works, or if you have a switch matrix, etc.
As you may know a relay is an electrically-operated and electrically-isolated switch so it can be wired in parallel with an existing switch with no worries.
And with a momentary switch there is no issue of a conflict (as long as the relay is operated momentarily).
I think you can daisy chain Toshiba controllers on the 2-wire bus. If the Arduino doesn't insert a signal into the lines I'm hoping it would just be seen as a dead/null device on the bus.
