Regular readers will remember my efforts to add remote control to the garage door shutter with a Shelly 2.5.

This had all been working fine, but then I had to replace the old Ellard controller with something else - something which actually provides a safety cut-out and allows you to legally have the door close on its own without a person having to keep their finger on the button.

And at this point, it ocurred to me that wiring the Shelly 2.5 back in would defeat the point of having a safety cut-out, since the Shelly is effectively in parallel with the controller and won’t respond to the controller trying to issue a stop because there is an obstruction.

What would be really nice is if the Shelly could operate the 12v terminals designed for connection of a key switch, much like my relays on the Raspberry Pi board did in v1.0 some years back.

But, the Shelly 2.5 puts 240V AC onto its switch outputs, so what to do?

There are various articles out there about how to convert a Shelly 2.5 to provide two dry contact relays, and they all start with “break the case open, get a soldering iron …”.

Nuts to that.

Anyone with basic knowledge of electronics knows that the way to control one circuit with another is a relay.

And while it’s quite unusual to use a “high power” (240V AC) circuit to switch a low power (12V) one, there’s no reason it can’t be done.

So all I needed was a couple of mains powered dry contact relays:

Relays in situ

I need to get some heat shrink on to tidy this up, but it works, and it’s much safer.