Wemos D1 R32 pinout: every Uno hole, and the ESP32 GPIO behind it

The Wemos D1 R32 is a classic ESP32 on the Arduino Uno’s outline, with an ESP32-WROOM-32 module where the Uno’s chip would be and the Uno’s four headers in the Uno’s places. The holes carry the Uno’s names, but a sketch writes GPIO numbers, and the two do not match: the hole marked D2 is GPIO 26. This page lists every hole with its GPIO, the power pins, the input-only pins, the strapping pins, the onboard LED and which pin to use for what.

The circuit above is the board in Mokxi with a button on the hole printed D2, GPIO 26, lighting an LED on D3, GPIO 25, and the blue LED with it. Everything in the table is checked against the board model the simulator runs, and where Mokxi does less than the chip, the row says so.

IOREF is 3.3 V, because the board’s logic is 3.3 V, and that is the thing a 5 V shield needs telling. 3V3 is the regulator’s output, enough for a sensor, not for a motor. 5V is the USB rail. VIN is the barrel jack’s side of the 5 V regulator. The three GND holes are one ground.

Every GPIO is 3.3 V and none is 5 V tolerant, so a shield made for a 5 V Uno can plug in and still damage a pin if it drives one to 5 V. Give a 5 V output a divider or a level shifter. In Mokxi the board is always powered from USB: VIN and AREF are open, and the regulator is not modeled, so a circuit that would overload the real one still runs here.

A2 to A5 are GPIO 35, 34, 36 and 39. On the ESP32 those pins have an input buffer and nothing else: no output driver and no internal pull-up or pull-down. They make good analog inputs, all on ADC1, and they cannot be outputs. A button on one needs a 10 k resistor of its own.

Mokxi refuses an output on these pins the way the chip does, so a sketch cannot believe it is driving one.

The blue LED is on GPIO 2 and lights when the pin is HIGH. LED_BUILTIN is 2. GPIO 2 is also the A0 hole, so anything wired to A0 shares the pin with the LED.

Only ADC1 reads in Mokxi, and on this board ADC1 is A2 to A5. A0 and A1 are GPIO 2 and 4, on ADC2, and analogRead on them reads 0 here. On a real board ADC2 works only while WiFi is off. ADC1 is twelve bits, 0 to 4095, with a real part’s curve at the default 11 dB: a pot across 3.3 V reaches 4095 at about 3.1 V.

PWM is LEDC, on any pin with an output driver. Wire.begin() uses SDA, GPIO 21, and SCL, GPIO 22, and SPI uses D13, D12, D11 and D10, GPIO 18, 19, 23 and 5, for SCK, MISO, MOSI and SS, so an Uno shield that uses SPI finds it in the same place. In Mokxi both buses run in software on those pins, because the chip’s I2C and SPI controllers are not modeled.