The Wemos D1 mini

The NodeMCU's ESP8266 on a board a third the size, with the same pin names and only the pins that do something.

What it is

An ESP-12F module, which is an ESP8266 with its flash chip under a tinned can, on a board 34.2 by 25.6 mm with two rows of eight holes 0.9 inch apart and a micro-USB socket on the end. It is the chip the NodeMCU carries, and it runs the NodeMCU's programs: a sketch that says D1 means GPIO 5 on either board.

Pins

With the antenna at the top, the left row reads RST, A0, D0, D5, D6, D7, D8 and 3V3, and the right row reads TX, RX, D1, D2, D3, D4, GND and 5V.

The silkscreen's D numbers are not GPIO numbers:

Pin	GPIO	Also
D0	16	no interrupt, no PWM
D1	5	I2C SCL
D2	4	I2C SDA
D3	0	pulled up on the board
D4	2	the blue LED, pulled up
D5	14	SPI SCK
D6	12	SPI MISO
D7	13	SPI MOSI
D8	15	pulled down on the board

• D4 carries the ESP-12F's blue LED, wired from 3.3 V to the pin, so it lights when GPIO 2 is LOW. It is LED_BUILTIN.
• A0 is behind the same 220k and 100k divider the NodeMCU has, so the hole reads 0 to about 3.2 V.
• 5V is the USB rail and 3V3 the regulator's output, both supplies for the breadboard.

The NodeMCU's six flash wires, its two reserved pins, EN, its second LED and its FLASH button are not on this board.

The programs

Its processor is an Xtensa LX106, the NodeMCU's chip, and your own sketch compiles in the tab the same way: edit it and press Run. The NodeMCU's Blink lights the blue LED on D4 and an LED you wire to D1.

WiFi

The board joins Mokxi's simulated network, as every WiFi board here does. The network name and password are properties of the board. There is no radio, no 802.11 and no real internet: Simulated WiFi says what is there and what is not.

What is modeled and what is not

Everything the NodeMCU model does, on sixteen holes. Not modeled: the CH340 USB-serial chip (Serial reaches the monitor directly), the reset circuit that lets the USB port reset the board, deep sleep's wake from D0 to RST, and the regulator's limits.

Starter project

D1 mini blink is the board across a breadboard with an LED on D1, running the NodeMCU's Blink: the blue LED on the module and the wired one are always opposite, because one lights on LOW and the other on HIGH.