Sonoff 5V Inching/Selflock Module RE5V1C Relay
GPIO1 ETX GPIO2 IO2 GPIO3 ERX GPIO4 RX GPIO5 TX
Please see the Hardware Preparation page for general instructions.
Access the serial interface by soldering wiring to the labled solder pads as shown in the image above - (3V3, ERX, ETX, GND) are available on the relay mounted side of the PCB. Note: use the ERX and ETX pins, not the two marked RX/TX.
To place the board into flashing mode, depress the surface mounted button switch on the reverse side of the PCB while power is applied. The used voltage regulator is a Low-Dropout Linear Regulator. Named as LM1117 which can deliever up to 800-mA.