Reddit mentions of Icstation 3V 1 Channel Relay Power Switch Module with Optocoupler Opto Isolation High Level Trigger for IOT ESP8266 Development Board (Pack of 5)

5pk 3v relays from Amazon. I had to get these when I switched from 5v Uno to 3.3v ESP32. My 5v relay wouldn't recognize the 3.3v as a high signal. Using to control 24VAC garage furnace.

Don't. Use something like these.

I'm sure you could find them cheaper on Aliexpress or eBay, but I use these exact ones with NodeMCUs, WeMos D1 Minis, and WeMos D1 Mini Lites all the time. They work great.

I'm not clear what you mean by I/O board? If it's just the gpio header on the pi itself, it's 3.3v but at 10mA, maybe 12mA? Enough to drive a signal, but not enough to energize a coil. (If you do have a separate board, you'd have to either lookup the specs for it, or let us know which one so we can figure it out.)

So you'll need something to use that to push a relay. Typically a darlington pair, an optoisolator, or a trip to Amazon.

I'm cheap and lazy, so I regularly use either these, which are 3v modules, or these which are awesome, but do need 5v drivers (I usually use an MCP23018 between the pi & the relay board - you'll find a shedload of documentation for this on the googles, but I'll shout-out adafruit's docs specifically). For the sainsmart ones, when they say 12V, they mean you'll need a separate 12V supply to push the relays themselves, they're not expecting 12V from the pi.

These will get the pi to drive n/c & n/o dry contacts you're used to, but I note you also asked about triggers - relay boards won't help protect inputs, so be warned that the inputs are also 3.3v and have very little tolerance (5v will kill them, let alone 24V. Anything you put in the IO lines goes straight into the CPU, so be gentle).


A couple of projects you might want to look into if you want to let someone else worry about the interfaces;

• Kunbus Revolution - not cheap, but Germans doing things the german way, to proper grownup specifications
  
• UniPi - looks more expensive, but works out well when you figure out how many Kunbus modules you'd need to get that many IO (if you just get the board that is. Their housings add grownup prices quickly)
  
• Pimoroni automation hat - Isn't trying to be industrial, isn't trying to charge industrial prices. When they say 'SRS BSNS' they mean 24v, not IEC61131. I went this direction in the end, because I'm cheap.
  
  

Love the push/pull analogy. Thanks for that one, makes sense. Kind of a supply vs demand situation.

Yes, same power supply but only interact via a relay: GPIO2 on ESP-01 goes high (+3.3v, remember I'm still learning terminology here) when triggered via message, opens 3.3v relay (https://amzn.com/B01M0E6SQM) which connects 12v via step-up to gate remote which has it's button locked on. So 5v source split into 3.3v step down and 12v step up, separated by the relay downstream.

The setup allows me to skip two important features: needing to deconstruct/integrate with the remote board to replicate a button press (which would have been destructive) and needing to power off a battery (would have required ongoing replacement & cost).

In case anyone has this same problem, this opto-isolator board seems to have fixed the issue.

I was having issues with the limit switches triggering prematurely also, so I installed four of these boards (one per limit switch and one for the probe circuit) and installed an add-on board using this circuit and the probe and limit switches are now working perfectly. :)