Sonoff Basic (or Shelly 1) in a 3-way switch configuration?

[Michael Ingraham]

Not explicitly a Sonoff question, but more generalized to include Sonoff Basic or Shelly 1. In either case I'd flash TASMOTA on the device.

I've added some smart switches to some of our lights and lamps and had been wanting to tackle placing a Sonoff Basic in the wall light switch housing for some of the lamps which are plugged in to a switched outlets. I also have a project started for our five ceiling fans... which are switched at the wall as well. With the availability of the compact Shelly 1, I've felt more at ease of taking this step. No need to hack the Basic to access GPIO14, no mix of low & high voltage, and getting it all to fit inside the circuit box. The Shelly 1 appears to address all of these. The fact that the Shelly 1 has all the pins already in place to easily allow flashing is a huge bonus!

I'm comfortable with understanding the setup for a single pole light switch. A physical three-way circuit scenario is less obvious... to me. I haven't found any examples, Sonoff, Shelly, or otherwise, that shows how to set up smart switching and physical switching for a three way light switch. The load would always be controlled by the smart switch. My sense is that I only need one smart switch in the mix; yes? Of the two circuit boxes on the walls where the 3-way switches are installed, the smart switch would be in the circuit box where I have access to the home's mains neutral (hopefully one of the circuit boxes has line & neutral available, otherwise a different approach is needed). The smart switch would be controlled wirelessly (e.g., via MQTT) or by the smart switch input signal. Then, rather than just one wall switch "signaling" the smart switch, the operation of either wall switch would "signal" the smart switch. As always, the home automation can control the smart switch to toggle the state of connected load.

Am I way off base?

Otherwise, needing to retrofit each wall switch to function as a single pole switch and needing neutral at each switch is probably a bridge too far for me. I don't want to get into re-wiring the house.

If my hypothesis is correct (i.e., only one smart switch required), what does that wiring look like? Of course, if there is already a tutorial on making three-way circuits "smart" or know of one, I'd be grateful if you would point me to it.

Regards.

Mike

[Philip Knowles]

There is a way to do this but you need to be confident of your house wiring. In the UK we use a loop in wiring system for lights. Live and neutral go to the ceiling rose (or junction box). A live feed then comes off the rose and goes to the switch. The feed then comes back to the lamp.

With a three way switch there is and additional wire between the switches but the end result is one wire that comes back to the lamp.

So, if you disconnect the switch feed from the rose and connect it to a GPIO and then take the return and connect it to GND. The switches operate as normal we’ve just changed the supply. The switch will then trigger the Sonoff. It can be overridden by wifi.

 

However you must be sure that no other AC supply can get into that circuit.

 

I’ve already done this with a bathroom light and extractor using a Dual. The light switch operates relay 1. The fan is operated by relay 2  after a timer and goes off after another timer

 

I’ll draw something up tomorrow.

 

Sent from Mail for Windows 10

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[Michael Ingraham]

Thanks Philip! The diagram will be really helpful for me to get my head around this.

In the US, electrical code allows the line and neutral to go to any of the three circuit boxes in the installation. So one has to know a little bit more about what one is doing and how to properly identify which circuit box to install the smart switch in. But your response is already helping. I had such blinders on that I hadn't even considered the ceiling rose (BTW, I had not heard that quite descriptive name used here in the US.).

P.S. Take a look at the Shelly (review by The Hookup). No messing about with low voltage & high voltage connections. No cracking the device open to solder or add inputs. It's built to be used as a "plain" smart switch or as a smart switch installed in a home's electrical circuit box. In fact, from what I gather, it's built to fit in EU (or at least German) circuit boxes specifically. It's nice and compact so it fits more easily in any circuit box, particularly US sizes. And the pins to flash it are already available externally to the circuitry (and recessed from getting short circuited). And they are reasonably priced.

[Phil]

The shelly does look like a great candidate for sensorless devices shut in small spaces, i caught a utube on it the other week but its not a cheap device at 3-4x the cost of a sonoff basic (£4 vs £15+) and iirc the gpio interface is live when wired into the mains prohibiting the use of additional sensors/h/w..  

Shelly vs sonoff Utube

[Michael Ingraham]

https://shelly.cloud/product/shelly-1-open-source/ - 9.90 €

So, for me, Sonoff for most applications; Shelly for switchbox applications.

Yeah - that the same Shelly review video I'd linked.

[Philip Knowles]

Here is the diagram as promised. This is how a 2 way switch system works in the UK (with UK wiring colours too – the blue wire to the lamp from the switch should have brown sleeving on – we use brown for live and green/yellow for earth). We use an ‘intermediate’ switch in between the two switches for additional switch points

The GPIUO is set as a switch1 and the normal light switches will switch the Sonoff output on and off. Importantly, wifi will also switch it on and off (even if the switch is on).

The Shelly1 looks to be a great piece of kit. Unfortunately, in the UK, we don’t have a neutral in our light switches (to save copper) but it is small enough to fit above a ceiling rose (where we do have neutral) and the switched live from the switch can be wired into Sw on the Shelly1.

[Michael Ingraham]

Thanks Philip. This helps tremendously!

My Sonoff (TASMOTA really) projects keep growing... but my available time seems to diminish :( Soldering leads to flash my S31 (for the washer monitor) is kicking my ass. Then I have to retrofit my ceiling fans with 4Ch controls... and then I'll tackle this one. The good news is that the Shellys are back-ordered so I can't do this one right now anyway ;-)