How to read non-voltage-free switches via Shelly

Hi folks,

In the past my (primitive) home automation has been growing organically with all kind of technologies I learned from people in this community. As a result it became a huge mess, which would unmaintainable for my familly if I ever would not be around anymore...

So we decided to go for a (nearly full) Shelly approach. And I have to admit that it looks MUCH better now, both the wiring and my flows. One of their devices I love the most is the Shelly i4 dc which allows me to measure the status of all my voltage-free switches (magnetic door contacts, relays of smoke detectors, water level sensors, ...):


The last thing I need to migrate to Shelly is the control of my 2 garage door openers. They are currently still connected to my Node-RED system for years via optocouplers, so now time to move on....

Each garage door opener has the following pins:

  • Pin 1: GND
  • Pin 3: VCC (24 Volt DC)
  • Pin 5: Microswitch that indicates if garage door is fully open
  • Pin 6: Microswitch that indicates if garage door is fully closed
  • Pin 10: To open/close the garage door --> I already use a Shelly switch Plus 1 to control this and works fine).

The problem is that pins 5 and 6 are NOT voltage-free relais, that I could measure with the wiring diagram above. Because these pins have the following values:

  • 24 Volt DC if the microswitch is open
  • 0 Volt if the microswitch is closed

So their voltage is delivered by my garage door opener, not by the Shelly...

Does anybody have an idea how I can measure something like that with Shelly devices? I assume I cannot do simply something like this:


Or can I use another Shelly type for this? Perhaps a Shelly Plus 2?


Because then I could use its build in relay to control pin 10, and thus replace my existing Shelly switch plus 1 device.

Hopefully somebody knows how I can do this. Then I have finally after all those years a setup that is easy to maintain.


P.S. I will try to share a short tutorial on Discourse during the weekend, to explain how you can easily use the Shelly i4 dc with Node-RED...

I have not used these but I think they may work for you

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Hi @E1cid,

Thanks for the assitance!!!

Am I correct that I need to measure the digital voltage that way, and then determine myself whether I consider the measured voltage as 0 or 1. Like my i4 dc does for me behind the scenes automatically.

If so, it is a pitty that I cannot use the Shelly Plus Addon for that purpose, because it would fit better into my din rail holders between my other shellies... But I think it's voltage range is not big enough.

Bart, I have not used them, but if they are like other shellies , they could possibly have actions . So you may be able to do this all internally, in shelly uni Shelly Uni Device Smart Control

din mount for uni Shelly UNI - Gehäuse / casing DIN-Mount by -Olsche- - Thingiverse

If you have a known voltage perhaps use an external relay. This would give you a clean set of contacts to use as a digital one or zero. Yes, it does increase parts count by one but you have a guaranteed clean input/output so no danger to either device
[Edit] and there are gobs of relays in all voltage ranges and ac/dc that DIN mount

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Ok so with the actions indeed I could simulate a 'normal' Shelly with the plus-uni. Thanks!

The din rail mount could indeed do the job. Will certainly take it into consideration!
The stupid thing is that I had everything replaced by Shellies, and left a couple of din rail holders free for my garage door opener related Shellies:

So a bit pitty that there is no 'normal' shelly that can do the job, because that would fit nicely into my cabine...

Hi @gerry,
Could you explain this a bit in detail, how that should work?

For anybody interested in this topic, I see here that the digital input of a Shelly Plus Addon works like this:

  • -15 V to 0.5 V (True)
  • 2.5 V to 15 V (False)

So its voltage range indeed does not go until 24 V DC.

Connect a relay to your contacts of the door opener so the relay energizes and deenergizes with the door. You now have a set of contacts that opens and closes with your door. These contacts are completely isolated from everything. Now take one side of the contacts to an input on your Shelly, the other side to either plus or ground on the shelly , now you have a circuit with no external voltage on the Shelly that tells you open or closed. You will need a pull up or pull down depending on the connection.


Based on all the input, I am now tempted to go for one Shelly Uni for each garage door opener. With a din-rail holder, it looks like a decent solution: very simple wiring, similar web interface as my other Shellies, supports MQTT like my other Shellies.

When I look at the wiring diagram of Shelly Uni, it looks to me like my garage door opener sensors behave like in the part highlighted with the red arrow:

That would mean that the wiring between my garage door opener and a Shelly Uno could be very simple:

Description Garage door opener Shelly Uno
GND pin 1 pin 2
VCC (24 Volt DC) pin 3 pin 1
Sensor door open pin 5 pin 7
Sensor door closed pin 6 pin 8

Unless somebody sees a blocking error (through his electronic glasses...), I am going to order a couple of Uno's...

Looks like a good option Bart.
Do Shelly now do a case for the Uni, to attach it to a din-rail?
I haven't looked at their full range of accessories, but I bought some Uni's when they were first released, and had to use joint boxes from the local hardware store.
The Uni's are smaller than you'd probably expect, but work really well.

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Yes the one that @E1cid shared:

Can buy them e.g. here as a bundle. Rather expensive, but then at least I don't have them flying somewhere in the air my IOT closet...

The one thing I find pitty about the Shelly Uno's is that they don't have terminal blocks like the other Shellies, so I need to start soldering...

I prefer soldering, but there are other options to join wires, terminal strips etc...

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So, if you want to be remembered in a positive way by your family, give up on all that and install simple ON/OFF switches :wink:

Hi @ebolisa,
Well in fact you are absolutely right. My rule of thumb is: it should work also without shelly/wifi/Node-RED. So in this case I have a physical wall switch for every garage door. And the sensors are already being used by the garage door openers itself, which is why there is already 24 V on those sensor switches.

And everything extra is luxury and hobby...

Of course the Shellies are a bit tempting to sin against this rule. Because they can also operate standalone (without wifi/Node-RED) and they have SW inputs to attach directly phisical switches to them. And they are easy to replace. But I still try to not use them in the old critical paths, which always need to keep working...

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