ESP8266

The venerable Esprissif chip with wifi, and the foundation for so much Internet of Things shit in the world.

The ESP-8266 is readily available in a dozen variants. These are my notes for the ones I most often use:

Wemos D1 Mini pinout

NodeMCU v3 board and pinout

General ESP8266 notes

The ESP-8266 (and 8285 variant) is a 3v3 microcontroller. The GPIO pins are 5V tolerant for binary inputs, but it's probably not a good idea to go throwing 5v data lines around with it.

If you're not using a DEV (Wemos / NodeMCU / etc) board:

• Pull RST (reset) HIGH to keep it from floating. (GND it to hw reboot)
• Pull EN (enable) HIGH to make device run.

GPIO dragons

At first blush it looks like the ESP-8266 has lots of GPIOs, but in reality only about half a dozen are universally usable. Common stumbling blocks / warnings:

• The pin numbers on Wemos / NodeMCU / &etc "dev boards" don't match the ESP-8266 datasheet GPIO numbers. Refer to the pinout diagrams to see the actual mappings.
• GPIO1, GPIO2, GPIO3, GPIO16 all strobe HIGH at boot. If you put a transistor or relay on them, be prepared for it to intermittently strobe high uncommanded every time the uC reboots.
• GPIO0, GPIO2 are pulled-high, and device will not boot if they're pulled low.
• GPIO1 (TX) will cause device not to boot if pulled low.
• GPIO15 is pulled low and device will not boot if pulled high
• The raw A0 analog input pin is 0-1VDC. The "dev boards" (NodeMCU, Wemos D1 &etc) all put a 3.3:1 voltage divider network in front of it. So be aware of the specific implementation you're using

Flashing

The default way to flash the program space in an ESP-8266 is to tie GPIO0 to GND during boot, this puts the device into firmware update mode.

Modern dev boards can be reset and flashed via the USB port using the esptool.py (which is also utilized by PlatformIO)

Momentarily grounding RST will reset the device. Tie RST high (if not already) the rest of the time to prevent it from floating.

ESP-12F Module and pinout