Sonoff Basic Voltage Free Relay Changeover Modification

What is Sonoff –

Home automation is “The Internet of Things”. It simply means the way all devices or appliances are networked together to provide customers with a seamless control over their home equipment.

Sonoff is an affordable device that provides users with smart home control. It is a WiFi based wireless switch that can connect to a wide range of appliances. Sonoff transmits data to a cloud platform through the WiFi router, which enables users to remotely control all the connected appliances, via the mobile application eWeLink. The cloud server of Sonoff is Amazon AWS global server.

Sonoff makes all home appliances smart. As long as the mobile has network, users can remotely control the appliances from anywhere at any time. Another feature available is to set timing schedules for the appliances, which can include countdown, scheduled on/off, and can thus, help users maintain an easy life.



The unit I needed to modify was the Sonoff Basic, this is a simple WiFi enabled unit which will switch 230v on or off, however, the application I needed was for it to switch a set of voltage free contacts, as these cost less that £6.00 each, its worth a go with the soldering iron.sonoff

The unit is very compact and before starting, I paired it with my mobile phone and checked that it worked correctly.

Sonoff open

The top simply clips off the base and the PCB comes apart without any fixings after cutting the paper security seal.



The relay has the Sonoff sticker on it and the mains is switched through the relay, the board uses double sided tracks for this.


The relay was desoldered and removed from the PCB, this then allowed access to the tracks which were cut with a Dremel.

bottom cut

The picture shows the bottom of the PCB with the tracks cut from the 230v input and a shorting link to complete the relay switching circuit.

top cut

This shows the relay back in place and the top tracks cut, the modification now allows a voltage free changeover which will be used to bring on my low voltage triggered external lighting.

Lighting Sonoff

Sonoff installed and connected to controller.

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10 thoughts on “Sonoff Basic Voltage Free Relay Changeover Modification”

  1. Thanks for the reply. I was able to replicate your switch. I’m not real sure I have a use for it. I just wanted to try. These Sonoff switches are just so hackable. I wish I could provide 3.3v or 5v to activate a solid stage relay.

  2. I did the exact same modification before I saw this article. I used a 12in hacksaw with the rounded end snapped off to allow cutting into a tight space (24 tpi), to cut the track which can be done without removing the relay.

    Initially I was going to use the basic SV model which is supplied without case but identical in dimension. The draw back is the manual switch has a low button which doesn’t reach the hole, though it fits the basic case perfectly otherwise.

    Current drain of the basic is 8.8mA and 12mA with a 130v supply from an isolating transformer.

    The SV model with an input of 5v running in isolated mode is 40mA and 80mA with the relay operated.

  3. I’ve not done the modification to a TH16 as the one I have needed to switch a voltage rather than give a volt free contact, I can’t see any reason why it can’t be done following the same steps as I did with the Basic.

  4. Hi,

    The safest thing to do is to unsolder the relay and extend the leads to the relay coil, then solder wires onto the relay contacts, I thought I could give you a drawing based on the link images, but without me trying it first could end in disaster

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