The ESP8266 has a current limit of 12ma, so we have to take care when driving relays. First I start with a 817C Optoisolator. The datasheet says says the IR LED drops 1.2v, so I plug 3.3v source voltage, 1.2v forward voltage, and 12ma forward current into the calculator at http://led.linear1.org/led.wiz and I get a 180 … Continue reading Driving Relays with the ESP8266