Solutions for smart bulbs with no neutral

Hi, I would like to note my experiences with installing smart bulbs while retaining my no-neutral switches.

I live in Germany and the light switches in my flat don’t have neutral wires installed. Now, I installed smart bulbs because I like the idea of having lights that change their colour temperature according to the sun. Also, I’ve configured my lights to turn on when my alarm goes off, just to annoy me harder out of bed. But that’s another story.

I wanted to retain my regular switches, but I changed them to push buttons by installing a little spring. Also, I didn’t want to rely on radio-only solutions just in case my HA server crashes or what not. Hence, I would like to use Shelly 1’s which can be coded to work as a decoupled switch when HA works but cut off power regularly when HA is not working. Shelly 1’s require a neutral connection, Shelly 2L’s don’t work with smart bulbs and SONOFF ZBMINI-L2’s don’t have a decoupled mode.

Also, the problem is that when I cut off power using my switch, then … well … the bulbs get no power and cannot be controlled otherwise. Also I noticed that automations don’t play well with lamps that are turned on by supplying power rather than sending a command.

So, I’d like to present you the solutions I found.

Before we start: These solutions require you to work with mains voltage! ALWAYS flip the breaker first before working on mains voltage! If you don’t know what you’re doing or don’t feel comfortable doing this, call a qualified electrician! You have been warned. Click below to see the solutions if you want to proceed.

Solution 1: (Easy) Use toggle function of smart bulb

This is the easiest solution but I figured that out at the very last (duh).

Requirements: This requires that you change your switch to a button. And the button must be configured to supply power by default, only cutting off power when you push the button. Also, the start behaviour (when powered on) needs to be configurable.

Steps: Change the “start behaviour” setting of each bulb in that circuit to “Toggle”. That’s it.

How it works: This way, power is almost always supplied to the bulb, while only cutting off power for minimal periods of time to signal the bulb to turn on/off.

Drawbacks: As there are capacitors in the bulbs that need to drain first, you may not let go of the button too quickly or else the bulb won’t register the power loss and hence remain on/off. Also, you can’t use Shellys or other relays with this solution.

Solution 2: (Difficult) Get neutral wires from another circuit

Requirements: Neutral wires running past the mounting box.

Steps: If there is a wall plug right below your switch’s mounting box or another circuit’s wires running past that box, you could wire these into your mounting box to supply your relay device with a neutral line.

Drawbacks: It’s likely that the wires running past the mouning box belong to a different circuit than your light. You’ll need to measure that out. If so, your device must be potential-free like the Shelly 1. Also, label the cables! Don’t mix up the circuits!

Solution 3: (Intermediate) Build a circuit hack to send commands

This solution was brought up by “My Project Box”:

Requirements: A wifi relay and smart bulbs that tolerate being supplied with DC, three resistors, two capacitors, two diodes and an octocoupler. Also, you either will have to solder these components onto a board or connect them with wagos or similar. Note: Use 10A10 diodes instead for good measure.

How it works: This clever trick uses one half of the AC spectrum to send signals while using the other half to supply power. By connecting a diode in parallel to your light switch, power is permanently supplied to the circuit, but only through one half of the AC spectrum:


When you turn on the switch, full wave AC is supplied:


We can use this to send signals to our Shelly. For that, an octocoupler circuit is used that registers changes in the AC spectrum and opens/closes the circuit respectively. That way, the Shelly knows if the switch was toggled.

Steps: Follow the video for details.

Drawbacks: You’ll need to build the circuit and install the Shelly in the ceiling rose. Also, you need to make sure that your bulbs tolerate being supplied with DC. innr comfort GU10 bulbs even tolerate being supplied with half-wave DC, as it has an internal rectifier that turns AC into DC. The package lists AC only, though, so don’t rely on that. If your bulbs tolerate half-wave DC, you don’t even need to use the second capacitor and diode as outlined in 06:05.

I hope that this helps out some of you folks! I had spent quite some time on finding solutions so I hope that I can spare some of your time!