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https://forum.arduino.cc/index.php?topic=490415.0 http://www.forward.com.au/pfod/ESP8266/GPIOpins/ESP8266_01_pin_magic.html https://www.instructables.com/id/Using-the-4-Pins-of-the-ESP8266-01/ https://randomnerdtutorials.com/esp8266-pinout-reference-gpios/ https://www.forward.com.au/pfod/ESP8266/GPIOpins/ESP8266_01_pin_magic.html https://www.instructables.com/id/ESP0101S-RELAY-..