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UM TinyS3
A compact development board from Unexpected Maker, offering wireless connectivity and ample Flash and PSRAM in a small form factor.
35 × 17.8 mm
ESP32-S3
MCU
240MHz
clock
8MB
flash
512KB
SRAM
19· 9 ADC
GPIO
BLE 5.0+ WiFi
radio
Pinout
19 pins| Pin | GPIO | Labels | Status | Capabilities | Notes |
|---|---|---|---|---|---|
| 1 | 1 | A0T1PWM | safe | adc · touch | |
| 2 | 2 | A1T2PWM | safe | adc · touch | |
| 3 | 3 | A2T3PWM | strapping | adc · touch | |
| 4 | 4 | A3T4PWM | safe | adc · touch | |
| 5 | 5 | A4T5PWM | safe | adc · touch | |
| 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 | VBAT_SENSEPWM | strapping | - | |
| 11 | 17 | RGB_PWRPWM | safe | - | |
| 12 | 18 | RGB_DATAPWM | safe | - | |
| 13 | 33 | VBUS_SENSEPWM | strapping | - | |
| 14 | 34 | SSPWM | strapping | spi | |
| 15 | 35 | MOSISDOPWM | strapping | spi | |
| 16 | 36 | SCKPWM | strapping | spi | |
| 17 | 37 | MISOSDIPWM | strapping | spi | |
| 18 | 43 | TXPWM | strapping | uart | |
| 19 | 44 | RXPWM | strapping | uart |
Start with these
9 pins with no boot or system involvementA0T1A1T2A3T4A4T5A5T6A6T7SDAA7RGB_PWRPWMRGB_DATAPWM
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 |
| 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 |
| VBAT_SENSE | FSPICS0 | Used to select the external flash chip. It is required for flash access and cannot be repurposed without losing flash connectivity | Flash |
| VBUS_SENSE | FSPIHD | On chips/modules with integrated flash, this IO is wired to the flash hold pin internally. It cannot be reassigned to GPIO without breaking flash access. | Flash |
| SS | 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 The UM TinyS3 pinout brings out 19 GPIO pins - every one of them usable in your project. For peripherals, I²C is mapped to SDA on GPIO8 and SCL on GPIO9; the…
The UM TinyS3 pinout brings out 19 GPIO pins - every one of them usable in your project.
For peripherals, 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.
On the analog side there are 9 ADC-capable pins for sensors and battery monitoring and 9 capacitive-touch inputs.
If you want zero surprises, A0, A1, A3, A4 and 5 more are free of any such role - the safest first picks. 3 of the exposed pins carry boot-time or system duties on the ESP32-S3 (A2, TX and RX).
Getting started
flash your first firmware in ~2 minutes1
Connect over USB
Native USB - no driver, no serial chip. Not detected? Hold BOOT while plugging in.
2
Flash with your tool
Arduino IDE, PlatformIO, ESPHome or esptool - copy the settings on the right.
3
Verify it runs
The blink example uses GPIO1 - swap for your board's LED pin if different.
Board: Tinys3
USB CDC On Boot: Enabled
Flash Size: 8MB · DIO
Upload Speed: 921600
// blink
pinMode(1, OUTPUT);
digitalWrite(1, LOW); // on (often inverted)[env:tinys3]
platform = espressif32
board = esp32-s3-devkitc-1
framework = arduino
monitor_speed = 115200
upload_speed = 921600esp32:
board: esp32-s3-devkitc-1
variant: um_tinys3
framework:
type: esp-idf
# blink - GPIO1
output:
- platform: gpio
pin: 1
id: led_out
light:
- platform: binary
name: "LED"
output: led_outesptool.py --chip esp32s3 --port /dev/ttyACM0 \
write_flash 0x0 firmware.binBuild details: sketch space 1310720 B · data 327680 B · DIO
Specifications
ESP32-S3 · 35 × 17.8 mmCompute
MCU
ESP32-S3
Clock
240 MHz
SRAM · Flash
512 KB · 8MB · 8MB (QSPI) PSRAM
Radio
Wi-Fi
802.11 b/g/n
Bluetooth
5.0 LE
Antenna
3D
I/O
GPIO · ADC
19 · 9
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
35 × 17.8 mm
The UM TinyS3 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
At its core is the ESP32-S3 - a dual-core Xtensa with vector extensions suited to AI workloads.
Expect to pay about $20.00 - less than the ~$30 most ESP32-S3 boards go for.
Onboard you'll find 8MB (QSPI) PSRAM, an addressable RGB LED (GPIO18), battery charging 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.
- Battery via header pins + a top JST-PH connector; single 700mA 3V3 LDO; VBAT voltage sensing on GPIO10
- Onboard 3D (ceramic chip) antenna
Where to buy
prices are typical street pricesUM TinyS3
$20.00per unit, typical
Resources
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