ESP32-C3 pinout: every GPIO, every ESP32-C3-MINI-1 pin, and the two pins that decide whether it boots

The MINI-1 is 13.2 × 16.6 × 2.4 mm with pads on a 0.8 mm pitch. Pads 1 to 11 run down the left, 12 to 24 along the bottom, 25 to 35 up the right, and 36 to 48 across the top, just below the antenna, all ground. Pad 49 in the middle is a ground pad made of nine squares, and pads 50 to 53 are the corner grounds. Many of the pads are not connected: the module only brings out the GPIOs the chip has free.

The ESP32-C3 chip is a QFN32, 5 × 5 mm. This table follows its GPIO numbers, which are also the numbers you use in code, and gives the MINI-1 pad for each one. “Free” means Espressif lists no restriction on it.

UART1, I²C, I²S, the TWAI (CAN) controller and the LED PWM outputs have no fixed pins: the GPIO matrix routes them to any free GPIO. The FSPI names are the pins the general-purpose SPI reaches directly through the IO MUX; through the GPIO matrix it can use other pins too.

Names and functions from Table 3-1 of the module datasheet.

Those are the variants Espressif lists as current; the older N4, H4 and H4-AZ are not recommended for new designs. The MINI-1U is 13.2 × 12.5 × 2.4 mm, has a connector for an external antenna in place of the PCB antenna, and uses the same pads with no antenna keep-out.

Three pins are read when EN goes high and latched until power-down. Espressif asks for them to hold their level for at least 3 ms after EN rises; after that they work as normal GPIOs.

With the Arduino core’s defaults for a generic ESP32-C3 board, SDA is GPIO8 and SCL is GPIO9, so an I²C bus sits on both boot pins. Its pull-up resistors give the right levels at reset, but a sensor that holds SCL low while the chip starts can send it into download mode. On your own board, put I²C on other free GPIOs.

GPIO18 (D−) and GPIO19 (D+) connect to the USB Serial/JTAG controller by default: a USB 2.0 full-speed port that gives you a serial console, flashing and JTAG debugging with no USB-to-UART chip. Wire them straight to a USB-C receptacle as a pair, and leave room for 22 to 33 Ω series resistors and small capacitors to ground (fitted only if needed) close to the module, as Espressif suggests. A USB-C receptacle also needs its own 5.1 kΩ resistor on CC1 and on CC2: USB-C CC resistors explains why.

Once firmware is running, tools can usually reset the chip into download mode over this port without touching the buttons. That stops working if the application turns the USB PHY off, uses the port as a USB host or device, or gives GPIO18 and GPIO19 to another peripheral; then you need the BOOT button. Espressif recommends keeping control of the strapping pins for that reason, and keeping the UART0 download interface too.

The ESP32-C3 has two 12-bit SAR ADCs. ADC1 reads GPIO0 to GPIO4 (channels 0 to 4) and is factory-calibrated. ADC2 has one channel, on GPIO5, is not calibrated, and does not work on some chip revisions, so Espressif recommends ADC1. The calibrated ranges from the hardware design guidelines:

• Attenuation 0: 0 to 750 mV, total error ±10 mV.
• Attenuation 1: 0 to 1,050 mV, ±10 mV.
• Attenuation 2: 0 to 1,300 mV, ±10 mV.
• Attenuation 3: 0 to 2,500 mV, ±35 mV.

A battery voltage above 2.5 V needs a divider, and Espressif suggests a 0.1 µF capacitor from each ADC pin to ground. The ESP32 battery charger circuit sizes that divider for a Li-ion cell.

Small boards print their own names on the pins. The Arduino core defines them in each board’s variant file; here are the two boards people ask about most:

The XIAO’s D0 to D10 are GPIO2, 3, 4, 5, 6, 7, 21, 20, 8, 9 and 10. That puts D8 and D9 on the two boot pins: a part that holds D9 low at power-up can send the board into download mode. The Super Mini’s Arduino variant uses plain GPIO numbers and puts its LED on GPIO8, one of the boot pins, so keep that pin free of anything that pulls it low at reset.

• Power: 3.3 V on pad 3 from a regulator that can deliver at least 0.5 A, with 10 µF and 0.1 µF at the module as in Espressif’s peripheral schematic.
• EN: never floating. An RC delay of 10 kΩ to 3V3 and 1 µF to ground lets the supply settle before the chip starts; add a reset button from EN to ground.
• Boot: a button from GPIO9 to ground, a pull-up on GPIO8, and a pull-up on GPIO2 as Espressif recommends.
• Flashing: USB-C to GPIO18 and GPIO19, or a USB-to-UART bridge to TXD0 and RXD0 (pads 31 and 30). Espressif recommends a 499 Ω series resistor on U0TXD to suppress harmonics.
• Antenna: put the antenna end at the edge of the board, ideally hanging past it, with no copper on any layer under it, and dense ground vias on the board next to it. Espressif recommends at least 15 mm of clearance around the antenna inside the enclosure.
• Ground: soldering the centre pad (49) is optional and helps with heat. Do not over-paste it, or the module sits too high for the edge pads to wet.

The ESP32 PCB design guide walks through the same support circuit on a finished board, from the regulator to the antenna keep-out.

PCBEditor’s part library carries the ESP32-C3-MINI-1 with Espressif’s own KiCad footprint, the same pads drawn in the figure above, beside the bare ESP32-C3 and the WROOM-02. The MINI-1’s antenna keep-out becomes a keep-out on your board that moves with the module: the copper pour, the router and the rules check keep copper out of it, and the KiCad export writes it as a rule area.

When PCBEditor draws the schematic for an ESP32-C3 board, it gives the chip a way to load its firmware: the USB port when GPIO18 and GPIO19 are wired to one, otherwise a programming header on UART0 (GPIO21 and GPIO20) with the boot line on GPIO9. It treats GPIO8 as a strapping pin that must be high: if nothing else on the board holds it, it adds a 10 kΩ pull-up to 3.3 V, and its electrical check reports a floating GPIO8 as an error.