Hello everyone,
Here I am with a short instruction on flashing another device with open source firmware, focused on local control. I’ve already flashed about 20 of these wifi wall switches, but at the time I didn’t have the forethought to document anything :oops:
So today is the day 
Long story short, Sonoff T3, 3 gang, EU model. Super easy to flash. you will need some leads (5), a serial TTL flasher, and either a second pair of hands or an USB extension cable, at least it helped me a lot.
Regarding software, grab this, runs on windows if you use it:
Simple double click, click to find the right usb port, select the release and press tasmotize! and that’s it.
Oh and sorry about some of the pictures, I was flashing the board while taking them, so they look kind of crap, my bad.
This is what we have to work with. The extra lead is to set the esp to boot mode.
While looking for documentation I found this thread which helped me a great deal. There I found the location of the GPIO0: TP1 (Key0) for my T3 3 gang. In some models it appears it’s TP0, so keep an eye for that.
I’m not particularly fussy so I just stood very still and flashing was successfull. Having more space to maneuver thanks to the USB extension cable really helped here.
And there we go: Got it flashed at the second try
What else… Configuration, the template is still the sonoff T1 1/2/3 gang, and it works great.
As an extra, because one of the relays is connected to an extractor fan I added one of these near the load, since I’ve had a previous relay malfunction after some months of work. Induction loads are bad for these little relays it would seem. It’s a Shelly RC snubber. super cheap, buy a couple, have them around.
And here it is installed, I didn’t take a picture with the cover because it would be a black square 
but they do look sweet!
What do you get with all of this effort?
A local solution;
A local Web Server to control the device;
An mqtt client builtin;
A rule engine, albeit a little limited, you can make some adjustments to the way the switches behave, I remember having a shutter mode even (preventing two relays being on at the same time);
It’s Tasmotized! Check out their github for more information about it
Final thoughts:
It’s 1h30 am, I’m tired and I will probably come back and add more details later, I just need some sleep
Flashing is really easy if you have someone help you, they just need to either plug the usb extension cord to the port, or hold any of the other leads in place.
It seems like the 1 gang and 2 gang version have a TP0 pin which is connected to the GPIO0. My T3 3 gang had a TP1 instead.
Oh I backed up my previous switch config and restored on this one, and openhab immediately picked it up too, so that was super cool.
In hindsight, and knowing what I know today, I probably wouldn’t go this route again. Sonoff will eventually phase these out sooner or later. If push comes to shove, they will work towards making them harder to flash, and as they continue to fail (This is the second one I had to replace since 2018) I will eventually run into sourcing problems - And I’m not even considering the cost here - So if anyone is reading this looking to make an informed decision, I have this to share with you:
Consider instead the zigbee in wall relays, and use normal run of the mill wall switches. Adding these in the wall, while it reduces the range of the zigbee antenna, if you have one per room will instantly make your zigbee network very capable. If one dies, they are easy enough to replace, and whether it’s an aqara, xiaomi, tuya, or bosch , as long as they are zigbee you’ll be fine as the switch on the wall will look the same. And as an additional benefit you don’t need to bother about flashing them, so i believe these to be a better option in the end.
That’s about it easy exercise in the end! Hope this helps someone out there!