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M5Stack-ATOM
Ultra-compact ESP32 board with RGB LED and button - ideal for simple wireless triggers and automation nodes.
24 × 24 mm
ESP32
MCU
240MHz
clock
4MB
flash
520KB
SRAM
19· Two 12-bit, 18 Channels ADC
GPIO
BLE 4.2+ WiFi
radio
Pinout
19 pins
| Pin | GPIO | Labels | Status | Capabilities | Notes |
|---|---|---|---|---|---|
| 1 | 0 | G0 | strapping | - | |
| 2 | 1 | TXPWM | uart | uart | |
| 3 | 3 | RXPWM | uart | uart | |
| 4 | 9 | G9PWM | strapping | - | |
| 5 | 10 | G10PWM | strapping | - | |
| 6 | 12 | G12PWM | strapping | - | |
| 7 | 19 | G19SSPWM | safe | spi | |
| 8 | 21 | G21PWM | safe | - | |
| 9 | 22 | G22SCKPWM | safe | spi | |
| 10 | 23 | G23MISOPWM | safe | spi | |
| 11 | 25 | G25DAC1PWM | safe | dac | |
| 12 | 26 | RXD2SDAG26DAC2PWM | safe | i2c · dac | |
| 13 | 27 | G27PWM | safe | - | |
| 14 | 32 | TXD2SCLG32PWM | safe | i2c | |
| 15 | 33 | G33MOSIPWM | safe | spi | |
| 16 | 35 | ADC1 | strapping | - | |
| 17 | 36 | G36ADC2 | strapping | - | |
| 18 | 37 | G37 | strapping | - | |
| 19 | 39 | G39 | strapping | - |
Start with these
9 pins with no boot or system involvementG19SSG21PWMG22SCKG23MISOG25DAC1RXD2SDAG27PWMTXD2SCLG33MOSI
Freely 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 |
|---|---|---|---|
| G0 | GPIO0 | Must be HIGH during boot for normal startup; if held LOW on reset, forces flash programming mode. | Strapping |
| G12 | MTDI (GPIO12) | Keep LOW during boot (internal PD); pulling HIGH at reset selects 1.8V flash mode, causing flash brownout if 3.3V flash is used. | Strapping |
| ADC1 | GPIO35 | Cannot be used as output; only suitable for input. | Other |
| G36 | GPIO36 (SENSOR_VP) | Cannot be used as output; only suitable for input (e.g., analog read). | Other |
| G37 | GPIO37 (SENSOR_CAPP) | Cannot be used as output; only suitable for input. | Other |
| G39 | GPIO39 (SENSOR_VN) | Cannot be used as output; only suitable for input. | Other |
Only if you know the tricks
wired to flash or USB - expect a fight| Pin | Label | What to know | Role |
|---|---|---|---|
| TX | U0TXD (GPIO1) | Connected to on-board USB-UART for uploading and logs; drives serial output at boot, so using as GPIO can disrupt programming or console. | USB |
| RX | U0RXD (GPIO3) | Used for receiving data from USB-UART (programming); also pulled HIGH at boot for console communication, so using as GPIO can disrupt uploads. | USB |
| G9 | GPIO9 (Flash SD2) | Used by internal flash/PSRAM; typically not exposed on modules, avoid using as GPIO. | Flash |
| G10 | GPIO10 (Flash SD3) | Used by internal flash/PSRAM; typically not exposed on modules, avoid using as GPIO. | Flash |
These are recommendations, not hard rules - with the right pull-ups, timing and boot-state awareness most pins can be made to work. When in doubt, start green.
Pinout notes The M5Stack-ATOM pinout brings out 19 GPIO pins - every one of them usable in your project. For peripherals, I²C is mapped to SDA on GPIO26 and SCL on GPIO32;…
The M5Stack-ATOM pinout brings out 19 GPIO pins - every one of them usable in your project.
For peripherals, I²C is mapped to SDA on GPIO26 and SCL on GPIO32; the SPI bus (MOSI, MISO, SCK, SS) is broken out in full; TX/RX on GPIO1 and GPIO3 cover serial logging and flashing.
On the analog side there are 2 true DAC outputs.
If you want zero surprises, G19, G21, G22, G23 and 5 more are free of any such role - the safest first picks. 6 of the exposed pins carry boot-time or system duties on the ESP32 (G0, G12, ADC1 and 3 more).
Getting started
flash your first firmware in ~2 minutes1
Connect over USB
Install your USB-serial driver (CH340 / CP210x) if no port appears. Not detected? Hold BOOT while plugging in.
2
Match & flash
Set the Tools options shown, then click Upload.
3
Verify it runs
The onboard LED on GPIO19 blinks - swap the pin if your board's LED differs.
Set these in Tools · leave everything else at default
Arduino IDE 2.x — Tools Copy
Board: "ESP32 Dev Module"▸
Flash Size: "4MB (32Mb)"▸
Flash Mode: "DIO"▸
Partition Scheme: "Default 4MB with spiffs (1.2MB APP / 1.5MB SPIFFS)" (default)▸
Upload Speed: "921600"▸
▸ every other Tools option — leave at default
Board: ESP32 Dev Module Flash Size: 4MB (32Mb) Flash Mode: DIO Partition Scheme: Default 4MB with spiffs (1.2MB APP / 1.5MB SPIFFS) Upload Speed: 921600
Find it: Tools ▸ Board ▸ ESP32 Arduino ▸ ESP32 Dev Module
// blink the onboard LED
void setup() {
pinMode(19, OUTPUT);
}
void loop() {
digitalWrite(19, HIGH); delay(500);
digitalWrite(19, LOW); delay(500);
}board to selectesp32dev⧉ copy
[env:m5stack-atom]
platform = espressif32
board = esp32dev
framework = arduino
monitor_speed = 115200
upload_speed = 921600Find it: PlatformIO Home ▸ Boards, search
esp32dev — or type it after board =.board to selectesp32dev⧉ copy
esp32:
board: esp32dev
variant: m5stack_atom
framework:
type: esp-idf
# blink - GPIO19
output:
- platform: gpio
pin: 19
id: led_out
light:
- platform: binary
name: "LED"
output: led_outFind it: search ESPHome's board list for
esp32dev (same ids as PlatformIO).esptool doesn't pick board settings — a prebuilt .bin already has them baked in. This is just the raw flash command.
esptool.py --chip esp32 --port /dev/ttyACM0 \
--baud 921600 write_flash 0x0 firmware.bin--port = your /dev/tty* (macOS/Linux) or COMx (Windows).Build details: sketch space 1310720 B · data 327680 B · DIO
Specifications
ESP32 · 24 × 24 mmCompute
MCU
ESP32
Clock
240 MHz
SRAM · Flash
520 KB · 4MB
Radio
Wi-Fi
802.11 b/g/n
Bluetooth
4.2 LE
Antenna
3D
I/O
GPIO · ADC
19 · Two 12-bit, 18 Channels
UART · I²C · SPI
3 · 2 · 4
PWM
16 channels
Power
USB
USB-C
Serial
-
Boot address
0x1000
Flashing
Upload · OTA
esptool_py · esp_ota
Flash · Boot mode
DIO · DIO
Sketch · Data
1.25 MB · 320 KB
24 × 24 mm
The M5Stack-ATOM uses esptool_py for firmware uploads, esp_ota for over-the-air (OTA) updates. Flash mode is DIO with DIO boot mode. The maximum sketch size is 1.25 MB with 320 KB available for data.
About this board
At its core is the ESP32 - a dual-core Xtensa with both Bluetooth Classic and BLE.
Expect to pay about $7.50 - less than the ~$20 most ESP32 boards go for.
Only 19 GPIO are broken out, where most ESP32 boards manage about 24 - worth checking the pinout covers what you need.
Onboard you'll find a Grove connector, an addressable RGB LED (GPIO27), an IR transceiver and User buttons.
Where to buy
prices are typical street pricesResources
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