In order to use the ESP-01 Wi-Fi relay module, a programmer/programming adapter is required to program the ESP-01 module (see below). Also it is pretty easy to make your own programmer, or you can ...

If so, remember to connect the VCC pin to 5V of the Arduino board to enable the control input pins IN1 and IN2. Also note at this point that, if you want perfect galvanic-isolation, do not link ...