Using With Sonoff S20¶
ESPHome can also be used with Sonoff S20 smart sockets. These devices are basically just an ESP8266 chip with a relay to control the socket, a small button on the front and a blue and green LED light.
This guide will step you through setting up your Sonoff S20 and flashing the first ESPHome firmware with the serial interface. After that, you will be able to upload all future firmware with the remote Over-The-Air update process.
If you’ve previously installed Sonoff-Tasmota on your Sonoff S20, you’re in luck 😀. ESPHome can generate a firmware binary which you can then upload via the Tasmota web interface. To see how to create this binary, skip to Step 3: Creating Firmware.
Since firmware version 1.6.0, iTead (the creator of this device) has removed the ability to upload a custom firmware through their own upload process. Unfortunately, that means that the only way to flash the initial ESPHome firmware is by physically opening the device up and using the UART interface.
Opening up this device can be very dangerous if not done correctly. While the device is open, you will be a single touch away from being electrocuted if the device is plugged in.
So, during this entire guide never ever plug the device in. Also, you should only do this if you know what you’re doing. If you, at any step, feel something is wrong or are uncomfortable with continuing, it’s best to just stop for your own safety.
It’s your own responsibility to make sure everything you do during this setup process is safe.
For this guide you will need:
Sonoff S20 😉.
A USB to UART Bridge for flashing the device. These can be bought on Amazon (or other online stores) for less than 5 dollars. Note that the bridge must be 3.3V compatible. Otherwise you will destroy your S20.
A computer running Home Assistant with the ESPHome Home Assistant add-on.
A screwdriver to open up the S20.
A soldering iron and a few header pins to connect the UART interface.
Have everything? Great! Then you can start.
Step 1: Opening up the Sonoff S20¶
The first step is to open up the Sonoff S20. Note that you do not have to run the original firmware supplied with the Sonoff S20 before doing this step.
Just to repeat this: Make absolutely sure the device is not connected to any appliance or plugged in before doing this step.
While the device is not plugged in, turn the back side so it’s facing you and unscrew the three black screws that hold the case together.
After that, you should be able to remove the front cover and should be greeted by a bunch of parts.
Step 2: Connecting UART¶
We’re interested in the main part of the S20 with the green PCB. On the bottom of the PCB, you will find four unpopulated holes. These pins expose the UART interface used to flash firmware onto the device and debug issues.
So, in order to flash our own custom firmware, we’re going to need to somehow connect the UART to USB bridge to these pins. The only way to make a good connection here is by using a soldering iron and soldering on some pin headers. On older models of the Sonoff S20, you were able to get the whole PCB out. Newer versions, however, glue the PCB onto the case to avoid people flashing custom firmware. If the latter is the case, you will just need to solder the pin headers from above - it’s a bit difficult, but possible.
When you’re done, it should look something like this:
Now go ahead and connect the pins to your UART bridge, making sure the S20 is not plugged in as before. Also beware that some UART to USB bridges supply 5V on the VCC pin if it’s not explicitly labelled 3.3V. It’s best to just use a multimeter and double check if it’s unclear.
On some older S20s, the
TX pins are swapped (sometimes even the written silkscreen is
wrong). If your upload fails with an
error: espcomm_upload_mem failed message it’s most likely due
to the pins being swapped. In that case, just swap
TX and try again - you won’t break
anything if they’re swapped.
Step 3: Creating Firmware¶
The Sonoff S20 is based on the
ESP8266 platform and is a subtype of the
With this information, you can step through the ESPHome wizard (
esphome sonoff_s20.yaml wizard),
or alternatively, you can just take the below configuration file and modify it to your needs.
esphome: name: <NAME_OF_NODE> platform: ESP8266 board: esp8285 arduino_version: 2.4.2 wifi: ssid: <YOUR_SSID> password: <YOUR_PASSWORD> api: logger: ota:
esphome sonoff_s20.yaml compile to validate the configuration and
pre-compile the firmware.
After this step, you will be able to find the compiled binary under
<NAME_OF_NODE>/.pioenvs/<NAME_OF_NODE>/firmware.bin. If you’re having trouble with
uploading, you can also try uploading this file directly with other tools.
Step 4: Uploading Firmware¶
In order to upload the firmware, you’re first going to need to get the chip into a flash mode, otherwise the device will start up without accepting any firmware flash attempts. To do this, while the UART bridge is not connected to your USB port, press and hold the small push button in the middle of the PCB. Then plug the UART bridge into your computer and keep holding the button for 2-4 seconds. The S20 should now be in a flash mode and should not blink any LED.
Now you can finally run the upload command:
esphome sonoff_s20.yaml run
If successful, you should see something like this:
Hooray 🎉! You’ve now successfully uploaded the first ESPHome firmware to your Sonoff S20. And, in a moment, you will be able to use all of ESPHome’s great features with your Sonoff S20.
If above step don’t work, however, here are some steps that can help:
Sometimes the UART bridge cannot supply enough current to the chip to operate. In this case use a 3.3V supply you have lying around. A nice hack is to use the power supply of NodeMCU boards. Simply connect 3.3V to VCC and GND to GND on the pins. Do not attempt to plug the device into a socket to overcome this problem while troubleshooting.
In other cases the
RXpin are reversed. Simple disconnect the device, swap the two pins and put it into flash mode again.
Step 6: Finishing Up¶
Now you’re pretty much done with setting up the Sonoff S20. The only steps left are to remove any cables that you added within the housing and make sure everything in there is clean. If, for example, you used wires to connect the UART console, you should definitely remove them to avoid a short with mains.
Sometimes the soldered-on header pins can also interfere with the button. It’s best to remove the header pins again, as you will hopefully not need to use them again because of ESPHome’s Over-The-Air Update features (+ the OTA safe mode; if your node reboots more than 10 times in a row, it will automatically enter an OTA-only safe mode).
If you’re sure everything is done with the S20 and have double checked there’s nothing that could cause a short in the case, you can put the front cover with the button on the base again and screw everything together.
Now triple- or even quadruple-check the UART bridge is not connected to the S20, then comes the time when you can plug it into the socket.