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#33: Sonoff Mini and S55: ALMOST perfect

The new Sonoff Mini DIY and Sonoff S55 are (so far) the best Sonoff devices that ITEAD has made. Flash them with Tasmota, and they get even better.

Resources

Background

The original Sonoff Basic didn’t have any provision for an external button or switch. One of the most common hacks is to add a switch, so ITEAD decided to make it easy and put screw terminals right there on the Mini.

The Mini is also the smallest Sonoff model so far, which makes it ideal for retrofitting behind an existing switch. Combined with the screw terminals to connect the switch, the Mini is probably the best general-purpose Sonoff for anyone wanting to retrofit home automation to an existing home.

The S55 is an exterior-rated GPO (General Purpose Outlet) or power point. It allows you to have both local control of the power point using a button, and also control from your home automation system.

Both are nice devices, but they become even better when the amazing Open Source Tasmota firmware is installed on them.

Over the years there have been many methods developed to do OTA (Over The Air) replacement of the existing Sonoff firmware with an alternative such as Tasmota. However, I’ve found that these methods are either frustratingly complex or just stop working because ITEAD change things with new releases. I don’t even bother trying these methods anymore: I just go straight to connecting a USB-to-Serial adapter to the programming pins on the Sonoff’s processor. It can be tricky to get the connections sometimes, but it’s guaranteed to work every time single time.

Warning: Do not attempt to connect a programming adapter to any Sonoff model while mains power is connected. ALWAYS disconnect the Sonoff and power it ONLY through the 3.3V connection.

Install Tasmota on Sonoff Mini

The programming connections for the Sonoff Mini are provided on tiny flat pads on the bottom of the PCB:

The button on the top of the PCB is connected to GPIO0, so if you connect to GND, 3.3V, TX, and RX, you can put the Sonoff Mini into programming mode by holding down the button while connecting power from the programmer.

Unfortunately the pads on the PCB are very small, so soldering jumper wires onto them is tricky. If you have a small soldering iron and good eyesight (or magnification) you can solder wires directly onto the pads.

Just be careful you don’t apply too much heat, because the pads can come away from the PCB!

To get around that problem I used my 3D printer to make a programming jig using a design published on Thingiverse. This programming jig uses “pogo pins”, which are spring-loaded pins that can make temporary connections to a PCB. Pogo pins come in a variety of sizes and shapes. I used P75-B1 pins, which means they have a 0.75mm diameter pin with a simple conical point:

This design has 3 parts: a base that holds 4 pogo pins, a small spacer that slips over the pins to help keep them aligned, and a top that goes over the pins and then provides alignment guides for the Sonoff Mini.

I used super-glue to attach the top to the base, once I’d checked everything was aligned:

The Sonoff Mini can be attached using an elastic band:

The pogo pins push against the pads on the PCB:

Hold down the button on the PCB while plugging in the programming adapter to force the Sonoff to go into programming mode, then you can use Esptool or whatever other method you prefer to load the Tasmota binary. In my case I used Esptool, and the command looked like this:

esptool.py -p /dev/tty.usbmodem141101 write_flash -fm dout 0x0 sonoff-6_6_0.bin

However, this command is specific to the USB port that I used on my computer. You may need to adjust the command to suit your needs. This is all documented well on the Tasmota site.

Because the Sonoff Mini has different pin arrangements to a normal Sonoff Basic, and it’s designed to use a normal switch instead of a button, you need to load a special configuration for it.

After you’ve been through the normal Tasmota setup process and connected it to your WiFi as described in the Tasmota docs, go to the Tasmota templates site at blakadder.github.io/templates/ and search for “Mini”. You’ll find a template that looks like this:

{"NAME":"Sonoff Mini","GPIO":[17,0,0,0,9,0,0,0,21,56,0,0,255],"FLAG":0,"BASE":1}

In the Tasmota interface, go to Configuration -> Configure Other and paste the template into the “Template” field.

Make sure the “Activate” check-box is ON, then click “Save”.

Your Sonoff Mini will now operate as expected, with the external switch operating in the normal way.

Install Tasmota on Sonoff S55

The Sonoff S55 doesn’t have a “DIY mode” jumper, so that’s not an option. Luckily, the usual programming header is provided on the PCB ready for you to solder on wires, solder on a header, or just press connections against it. The button for external control is linked to GPIO0, so it’s very easy to put it into programming mode.

The header is in the normal 0.1″ pitch so it’s large enough to solder on a header directly. There’s no need to use a complex pogo pin programming jig.

Solder some hookup wires directly onto the pads, or solder on a header:

I soldered a 4-way 0.1″ header socket onto the pads, with the pins bent a little sideways to make the head sit almost horizontal with the PCB. This makes it easy to plug in a Sonoff Programming Adapter, or use jumper wires to your own USB-to-serial converter.

Hold down the GPIO0 button while you connect the programming header to put it into programming mode, then follow the normal instructions for installing Tasmota. This is very well documented on the Tasmota site.

There’s no specific device profile for the S55 in Tasmota, but it uses the same pinouts as the Sonoff S26 and other mains-plug adapters. Simply select “Sonoff S2x” as the module type in the configuration interface, and it will work as expected.

4 thoughts on “#33: Sonoff Mini and S55: ALMOST perfect

  1. Thx for giving us another great tutorial……

    Glad that you are back

  2. Hi,
    Have a look at the following Amazon items:
    B07FKYT5G8 I have bought three (3) of these three (3) gang wall light switches and loaded Tasmota onto them. They work very well. They work manually as well as via the WiFi (in my case openhab).
    One actually drives two (2) down lights (left and right switches) the center switch communicates with openhab and it then Tx’s a IR code for the ceiling fan. 🙂

    I’m about to buy a couple of these GPO’s to give a try for things like Soldering Iron switches 😉
    B07S942V7L

    Just plug the above codes into the Amazon search bar.
    Neil

  3. can you please add the flsh gid to your online store? I would buy one and i’m sure others would also.

    1. I will as soon as it’s ready. I’ve done an updated version with auto-reset but the pinout on the programmer probably has to be changed before I release it. It’s all tied up with the “let’s make a standard programming header for ESP8266” discussion at the moment.

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