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UM FeatherS3
A Feather-format ESP32-S3 board with 16MB Flash and 8MB PSRAM, offering USB-C connectivity and support for various peripherals.
52.3 × 22.9 mm
ESP32-S3
MCU
240MHz
clock
16MB
flash
512KB
SRAM
22· 13 ADC
GPIO
BLE 5.0+ WiFi
radio
Pinout
22 pins · 2.54 mm pitch| Pin | GPIO | Labels | Status | Capabilities | Notes |
|---|---|---|---|---|---|
| 1 | 1 | A0T1PWM | safe | adc · touch | |
| 2 | 2 | A1VBAT_SENSEPWM | safe | adc | |
| 3 | 3 | A2T3PWM | strapping | adc · touch | |
| 4 | 4 | A3PWM | safe | adc | |
| 5 | 5 | SSA4T5PWM | safe | adc · touch · spi | |
| 6 | 6 | A5T6PWM | safe | adc · touch | |
| 7 | 7 | A6T7PWM | safe | adc · touch | |
| 8 | 8 | SDAA7T8PWM | safe | adc · touch · i2c | |
| 9 | 9 | SCLA8T9PWM | strapping | adc · touch · i2c | |
| 10 | 10 | A9T10PWM | strapping | adc · touch | |
| 11 | 11 | A10T11PWM | strapping | adc · touch | |
| 12 | 12 | A11T12PWM | strapping | adc · touch | |
| 13 | 13 | A12LED_BUILTINLEDPWM | strapping | adc | |
| 14 | 14 | T14PWM | strapping | touch | |
| 15 | 34 | VBUS_SENSEPWM | strapping | - | |
| 16 | 35 | MOSISDOPWM | strapping | spi | |
| 17 | 36 | SCKPWM | strapping | spi | |
| 18 | 37 | MISOSDIPWM | strapping | spi | |
| 19 | 39 | RGB_PWRLDO2PWM | strapping | - | |
| 20 | 40 | RGB_DATAPWM | strapping | - | |
| 21 | 43 | TXPWM | strapping | uart | |
| 22 | 44 | RXPWM | strapping | uart |
Start with these
7 pins with no boot or system involvementA0T1A1VBAT_SENSEA3PWMSSA4A5T6A6T7SDAA7
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 |
|---|---|---|---|
| A2 | GPIO3 | Sampled at reset to select JTAG interface (USB Serial/JTAG controller vs. external pins). Improper use can disable external JTAG or alter debug interface. | Strapping |
| RGB_PWR | MTCK (GPIO39) | Default JTAG debugging TCK pin. If JTAG is needed, this pin must be free; it may also be used internally for PSRAM chip select on certain modules, so avoid repurposing it. | Other |
| RGB_DATA | MTDO (GPIO40) | Default JTAG TDO output for debugging. Using it as GPIO will interfere with JTAG debugging functionality. | Other |
| TX | U0TXD (GPIO43) | Used for bootloader output and UART console logs. If repurposed, you will lose the default serial output (and programming via UART0). | Other |
| RX | U0RXD (GPIO44) | Used for bootloader input (download mode via serial). If repurposed, you cannot use the default UART0 download mode for programming the chip. | Other |
Only if you know the tricks
wired to flash or USB - expect a fight| Pin | Label | What to know | Role |
|---|---|---|---|
| SCL | FSPIHD | Connected to external flash (data/hold signal) on most modules. Not recommended for use as GPIO, since it must remain dedicated to flash communication. | Flash |
| A9 | FSPICS0 | Used to select the external flash chip. It is required for flash access and cannot be repurposed without losing flash connectivity | Flash |
| A10 | FSPID | Used as a data line for flash (and in-package PSRAM). It should not be used as GPIO when the flash/PSRAM is in use. | Flash |
| A11 | FSPICLK | Drives the flash (and PSRAM) clock. This critical signal must be reserved for memory and not used as general GPIO. | Flash |
| A12 | FSPIQ | Used as a data line for flash/PSRAM transfers. Not available for other uses when flash/PSRAM is connected. | Flash |
| T14 | FSPIWP | Connected to external flash (data/write-protect signal). Not recommended as GPIO because it’s reserved for flash operations. | Flash |
| VBUS_SENSE | FSPICS0 | Wired to the chip select of the internal flash in flash-equipped variants. It must remain low during flash operation, so it’s not available for other use. | Flash |
| MOSI | FSPID / PSRAM_D0 | In modules with octal PSRAM, this pin is connected to the PSRAM data line. It is reserved for memory interface and not free for general GPIO when flash/PSRAM is present. | Flash |
| SCK | FSPICLK / PSRAM_CLK | In modules with octal PSRAM, this pin drives the PSRAM clock. It must be dedicated to the memory interface, not used as a regular GPIO when that interface is in use. | Flash |
| MISO | FSPIQ / PSRAM_DQS | In modules with octal PSRAM, this pin is connected to the PSRAM’s DQS signal. It cannot be repurposed without disrupting the PSRAM/flash communication. | 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 All 22 pins on the UM FeatherS3 are usable GPIO, spaced at the standard 2.54 mm pitch. Peripheral wiring is straightforward: I²C is mapped to SDA on GPIO8 and…
All 22 pins on the UM FeatherS3 are usable GPIO, spaced at the standard 2.54 mm pitch.
Peripheral wiring is straightforward: I²C is mapped to SDA on GPIO8 and SCL on GPIO9; the SPI bus (MOSI, MISO, SCK, SS) is broken out in full; TX/RX on GPIO43 and GPIO44 cover serial logging and flashing.
Beyond plain digital I/O you get 13 ADC-capable pins for sensors and battery monitoring and 11 capacitive-touch inputs.
5 of the exposed pins carry boot-time or system duties on the ESP32-S3 (A2, RGB_PWR, RGB_DATA and 2 more) - check the guidance above before wiring anything to them. A0, A1, A3, SS and 3 more are free of any such role - the safest first picks.
Getting started
flash your first firmware in ~2 minutes1
Connect over USB
Native USB - shows up as a port right away, no driver needed. 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 GPIO1 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: "ESP32S3 Dev Module"▸
USB CDC On Boot: "Enabled"▸
Flash Size: "16MB (128Mb)"▸
Flash Mode: "DIO"▸
PSRAM: "QSPI PSRAM"▸
Partition Scheme: "16M Flash (3MB APP / 9.9MB FATFS)" (default)▸
Upload Speed: "921600"▸
▸ every other Tools option — leave at default
Board: ESP32S3 Dev Module USB CDC On Boot: Enabled Flash Size: 16MB (128Mb) Flash Mode: DIO PSRAM: QSPI PSRAM Partition Scheme: 16M Flash (3MB APP / 9.9MB FATFS) Upload Speed: 921600
Find it: Tools ▸ Board ▸ ESP32 Arduino ▸ ESP32S3 Dev Module
// blink the onboard LED
void setup() {
pinMode(1, OUTPUT);
}
void loop() {
digitalWrite(1, HIGH); delay(500);
digitalWrite(1, LOW); delay(500);
}board to selectesp32-s3-devkitc-1⧉ copy
[env:feathers3]
platform = espressif32
board = esp32-s3-devkitc-1
framework = arduino
monitor_speed = 115200
upload_speed = 921600
board_build.arduino.memory_type = qio_qspi
build_flags = -DBOARD_HAS_PSRAMFind it: PlatformIO Home ▸ Boards, search
esp32-s3-devkitc-1 — or type it after board =.board to selectesp32-s3-devkitc-1⧉ copy
esp32:
board: esp32-s3-devkitc-1
variant: um_feathers3
framework:
type: esp-idf
psram:
mode: quad
speed: 80MHz
# blink - GPIO1
output:
- platform: gpio
pin: 1
id: led_out
light:
- platform: binary
name: "LED"
output: led_outFind it: search ESPHome's board list for
esp32-s3-devkitc-1 (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 esp32s3 --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-S3 · 52.3 × 22.9 mmCompute
MCU
ESP32-S3
Clock
240 MHz
SRAM · Flash
512 KB · 16MB · 8MB (QSPI) PSRAM
Radio
Wi-Fi
802.11 b/g/n
Bluetooth
5.0 LE
Antenna
3D
I/O
GPIO · ADC
22 · 13
UART · I²C · SPI
3 · 2 · 4
PWM
8 channels
Power
USB
USB-C
Serial
Native (CDC)
Boot address
0x0
Flashing
Upload · OTA
esptool_py · esp_ota
Flash · Boot mode
DIO · QIO
Sketch · Data
1.25 MB · 320 KB
52.3 × 22.9 mm · pin pitch 2.54 mm
The UM FeatherS3 uses esptool_py for firmware uploads, esp_ota for over-the-air (OTA) updates. Flash mode is DIO with QIO boot mode. The maximum sketch size is 1.25 MB with 320 KB available for data.
About this board
Inside sits the ESP32-S3 - a dual-core Xtensa with vector extensions suited to AI workloads.
At $22.50 it's cheaper than most ESP32-S3 boards, which usually run around $30.
Around the module: 8MB (QSPI) PSRAM, a STEMMA QT connector, an addressable RGB LED (GPIO40), an ambient-light sensor, battery charging (MCP73831) via JST-PH 2.0 and Reset/Boot buttons.
It flashes over native USB - no serial-converter driver needed, which isn't a given among ESP32-S3 boards.
- Dual 700mA LDO regulators - second LDO (IO39) powers the RGB LED and a switchable 3V3 rail that auto-shuts down in deep sleep
- Onboard 3D high-gain antenna (a separate u.FL-connector variant is also sold)
Where to buy
prices are typical street pricesUM FeatherS3
$22.50per unit, typical
Resources
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