New video: how the T4EU1C no-neutral Sonoff touch switch works

Figuring this out was quite interesting, and it’s cool to see the scope trace that shows the load being switched off very briefly to allow the switch to vampire off a little bit of power.


That was a really cool explanation, electricity really is fascinating! It all makes sense now, what a stupidly simple idea.

My only thought is, exactly how big is the loss by using the capacitor box? Most of my use cases will be LED, so will likely need it to avoid the flicker issue.

I don’t think the loss will be significant, or at least it won’t be more than you’d have with a regular Sonoff Touch. The caps in the anti-flicker device act as a current limiter and the value that I calculated (0.3A) is the maximum that they will allow to pass at 50Hz. However, if the switch pulls less power than that, then less will pass through the circuit. My theory is that the power consumption of the T4 with the anti-flicker device is about the same as a normal Sonoff Touch powered using a neutral connection.

That’s really really cool and in hindsight makes sense. I bought a couple of the original Sonoff Touch’s, but with a double brick established home (most Perth homes are built this way) it was kind of a pain. It’s very common to just channel the wall with a concrete cutter, shove the wires in and “plaster” over them. So to add a Neutral would require destructive modifications and a lot of mess!

Modding them looks rather finicky though, it’ll be interesting to see if the release of the rectangle ones are similarly finicky.

There’s ongoing work to figure out more about the reflashing process, and why the touch switch doesn’t work for many people. For me it worked, and there are documented cases of it working for other people, but often it doesn’t. There are several theories at the moment, with the leading one being that the series resistor connecting the Holtek touch sensor IC to GPIO0 has a value that is too high, so it can’t overcome the bias of the internal pull-up resistor in the ESP8285.

I’ve been working with DrZzs and the Tasmota devs to figure it out. I only have one T4, and mine has been butchered, so I’ve been suggesting things for DrZzs to try and he’s been testing it.

Hopefully we’ll have an easier way before long, and also have sorted out the touch sensor.


I’ve just had a couple of the EACHEN version of this switch arrive this week. I will make a post about it with a couple of photos. Not had the chance to test it yet.