What is the best way to power the separate sides of an optically isolated relay circuit? Answered
I am working on a Raspberry Pi based thermostat for my air conditioner and have come across a variety of pre-made relay boards that would allow me to interface with the 24v AC control circuits. Most of the boards I have found have optoisolators that separate the input side of the board from the relay side of the board. I assume this is to prevent damage to the GPIO pins in the event of a mechanical failure of one of the relays.
These boards also have separate power inputs for the respective sides. I intend to use a bridge rectifier and voltage regulator so that I can power both the Raspberry Pi and relay board directly from the 24v AC line on the wall. My questions specifically is how I should isolate the power for both sides of the board. Do I need to have two separate bridge rectifiers and voltage regulators to essentially create two power buses or is there another acceptable way to protect the Raspberry Pi in the situation? Also, is the isolation even necessary in this situation?
The circuit diagram for the relay board can be found at http://imgur.com/UiXmfKC.
Thanks in advance for your advice.