“I wanted to have USB on the ESP8266, and a while ago I saw on the ESP32 flier, it read: “Rich Peripherals” … “Sorry, no USB!” I thought to myself, that is ridiculous. Of course there’s USB. So, it was born. This is a software USB stack running on the ESP8266/ESP8285. It requires only one external resistor, between D- and 3.3V. Currently, the chip expects D- on GPIO 4 and D+ on GPIO 5 - but any GPIO pair may be used. It is important to note that both D- and D+ MUST be adjacent.”