Flashing of WiFi Switch with a Raspberry Pi
There are many similar devices made by the same big company (Tuya) and redistributed by 3rd parties companies (like Sonoff, AVATTO, ...). These devices are natively integrated with the Tuya cloud which can operate the device remotely. For example, from the cloud it's possible to upload a new firmware via OTA.
If you consider this to be unsecure and a kind of leakage in your home network, you can flash the device with a open source firmware (Tasmota) which can be operated locally on your network, does not require a cloud, and can be integrated locally with other system like Domoticz, Home Assistant, Alexa, Google.
Devices produced up to early 2020, could be flashed with a Tuya cloud simulator, e.g. tuya-convert. The vulnerability has been fixed and tuya-convert cannot works anymore (see #483).
If you want to flash the Tasmota firmware, you need to open the device and connect a serial device (like a Raspberry PI) to the test points. A bit of reverse engineering needs to be done to map the testing point to the ESP chip pins.
For the ESP pinout, you need to check the Espressif datasheet. See for example:
- ESP8266 https://www.espressif.com/sites/default/files/documentation/0a-esp8266ex_datasheet_en.pdf
- ESP8255 https://www.espressif.com/sites/default/files/documentation/0a-esp8285_datasheet_en.pdf
This page applyes to a specific device: 
Precondition: Configure Raspberry PI inverting AMA and S0 serial in config.ini and cmdline.txt https://spellfoundry.com/2016/05/29/configuring-gpio-serial-port-raspbian-jessie-including-pi-3-4/ https://hallard.me/enable-serial-port-on-raspberry-pi/
Connection:
- connect RPI GPIO 5V to pin 3 of 5V/3V converted
- connect RPI GPIO TX to ESP serial RX
- connect RPI GPIO RX to ESP serial TX
- connect RPI GPIO GND to ESP GND
Steps:
- switch on the device with ESP GPIO0 shortcut on GND; this can be done by pressing the device button
- run esptool and flash the firmware
esptool.py erase_flash
esptool.py write_flash -fm dout 0x0 tasmota.bin
