ESP32 C3 Zero
Minimalist ESP32-C3 board with Wi-Fi & BLE - ideal for simple, budget-friendly IoT builds in tight spaces.
Pinout
18 pins · 2.54 mm pitch
| Pin | GPIO | Labels | Status | Capabilities | Notes |
|---|---|---|---|---|---|
| 1 | - | 5V | power | - | 5V power input for the board |
| 2 | - | GND | ground | - | Ground connection |
| 3 | - | 3V33.3V | power | - | 3.3V power output |
| 4 | 0 | IO0 | safe | adc | GPIO, ADC |
| 5 | 1 | IO1 | safe | adc | GPIO, ADC |
| 6 | 2 | IO2 | strapping | adc | GPIO, ADC |
| 7 | 3 | IO3 | safe | adc | GPIO, ADC |
| 8 | 4 | IO4 | strapping | adc | GPIO, ADC |
| 9 | 5 | IO5 | strapping | - | GPIO |
| 10 | 6 | IO6 | strapping | - | GPIO |
| 11 | 7 | IO7 | strapping | - | GPIO |
| 12 | 8 | IO8SDA | strapping | i2c | GPIO |
| 13 | 9 | IO9SCL | strapping | i2c | GPIO |
| 14 | 10 | IO10RX | uart | uart | GPIO, LED |
| 15 | 18 | IO18RX | uart | uart | USB DM |
| 16 | 19 | IO19RX | uart | uart | USB DP |
| 17 | 20 | IO20RX | uart | uart | GPIO, UART Receive (secondary) |
| 18 | 21 | IO21TX | uart | uart | GPIO, UART Transmit |
Start with these
4 pins with no boot or system involvementFreely assignable - no strapping, flash, USB or JTAG duties. Ideal first picks for buttons, sensors and LEDs.
Fine - with a little care
sampled at boot or shared with debug/serial| Pin | Label | What to know | Role |
|---|---|---|---|
| IO2 | GPIO2 | Must be held high during boot (if low on reset, normal flash boot may fail) | Strapping |
| IO4 | MTMS | Used during boot; JTAG TMS for debugging; acts as Quad-SPI flash IO (hold data line) in internal-flash variants | JTAG |
| IO5 | MTDI | Used during boot; JTAG TDI for debugging; acts as Quad-SPI flash IO (write-protect data line) in internal-flash variants | JTAG |
| IO6 | MTCK | Used during boot; JTAG TCK for debugging; provides flash clock in internal-flash variants | JTAG |
| IO7 | MTDO | Used during boot; JTAG TDO for debugging; acts as Quad-SPI flash IO (data line) in internal-flash variants | JTAG |
| IO8 | GPIO8 | Must be held high during reset (if low, UART flashing/boot may not work) | Strapping |
| IO9 | GPIO9 | Controls boot mode on reset (HIGH for normal flash boot, LOW enters serial download mode) | Strapping |
| IO20 | U0RXD | Used as UART0 receive (console/bootloader); repurposing may disable serial programming and debug logs | UART |
| IO21 | U0TXD | Used as UART0 transmit (console/bootloader); repurposing may disable serial console output and printing | UART |
Only if you know the tricks
wired to flash or USB - expect a fight| Pin | Label | What to know | Role |
|---|---|---|---|
| IO18 | USB_D- | By default connected to on-chip USB Serial/JTAG controller; to use as GPIO it must be reconfigured from its USB function | USB |
| IO19 | USB_D+ | By default connected to on-chip USB Serial/JTAG controller; not available for GPIO use unless USB functionality is disabled or remapped | USB |
Pinout notes The ESP32 C3 Zero pinout brings out 18 pins at a 2.54 mm pitch - 15 usable GPIO alongside the 5V , GND and 3V3 power rails. Peripheral wiring is…
The ESP32 C3 Zero pinout brings out 18 pins at a 2.54 mm pitch - 15 usable GPIO alongside the 5V, GND and 3V3 power rails.
Peripheral wiring is straightforward: I²C is mapped to SDA on GPIO8 and SCL on GPIO9, while TX/RX on GPIO21 and GPIO10 cover serial logging and flashing.
Beyond plain digital I/O you get 5 ADC-capable pins for sensors and battery monitoring.
9 of the exposed pins carry boot-time or system duties on the ESP32-C3 (IO2, IO4, IO5 and 6 more) - check the guidance above before wiring anything to them. IO0, IO1, IO3 and IO10 are free of any such role - the safest first picks.
Getting started
flash your first firmware in ~2 minutesBoard: Esp32c3 Dev
USB CDC On Boot: Enabled
Flash Size: 4MB · QIO
Upload Speed: 921600
// blink
pinMode(0, OUTPUT);
digitalWrite(0, LOW); // on (often inverted)[env:esp32-c3-zero]
platform = espressif32
board = esp32-c3-devkitm-1
framework = arduino
monitor_speed = 115200
upload_speed = 921600esp32:
board: esp32-c3-devkitm-1
variant: esp32c3
framework:
type: esp-idf
# blink - GPIO0
output:
- platform: gpio
pin: 0
id: led_out
light:
- platform: binary
name: "LED"
output: led_outesptool.py --chip esp32c3 --port /dev/ttyACM0 \
write_flash 0x0 firmware.binGood to know
board-specific quirks worth 60 seconds
Specifications
ESP32-C3 · 23.5 × 18 mmAbout this board
At 23.5 × 18 mm it's among the smallest boards in the whole ESP32 family.
Inside sits the ESP32-C3 - a single-core RISC-V and the budget low-power pick. Sibling Zero-format boards cover the ESP32-C6 and ESP32-S3, so you can change radios or horsepower without changing the footprint.
At $4.90 it's cheaper than most Zero-format boards, which usually run around $6.27.
Around the module: an addressable RGB LED (GPIO10) and Reset/Boot buttons.
It flashes over native USB - no serial-converter driver needed.
- Ultra-compact size: 23.5 × 18 mm
- Low power consumption: deep sleep current ~43μA
- Onboard WS2812 RGB LED (GPIO10)
Where to buy
prices are typical street pricesResources
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