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Bee S3
A compact ESP32-S3 development board designed for general-purpose IoT applications.
ESP32-S3
MCU
240MHz
clock
8MB
flash
512KB
SRAM
18· 8 ADC
GPIO
BLE 5.0+ WiFi
radio
Pinout
18 pins| Pin | GPIO | Labels | Status | Capabilities | Notes |
|---|---|---|---|---|---|
| 1 | 1 | VBAT_VOLTAGEPWM | safe | - | |
| 2 | 3 | A3D3T3PWM | strapping | adc · touch | |
| 3 | 4 | A4D4T4PWM | safe | adc · touch | |
| 4 | 5 | SSA5D5T5PWM | safe | adc · touch · spi | |
| 5 | 6 | A6D6T6PWM | safe | adc · touch | |
| 6 | 7 | A7D7T7PWM | safe | adc · touch | |
| 7 | 8 | A8D8T8PWM | safe | adc · touch | |
| 8 | 9 | A9D9T9PWM | strapping | adc · touch | |
| 9 | 10 | A10D10T10PWM | strapping | adc · touch | |
| 10 | 34 | RGB_PWRPWM | strapping | - | |
| 11 | 35 | MOSISDOD35PWM | strapping | spi | |
| 12 | 36 | SCLD36PWM | strapping | i2c | |
| 13 | 37 | SDAD37PWM | strapping | i2c | |
| 14 | 38 | MISOSDID38PWM | strapping | spi | |
| 15 | 39 | SCKD39PWM | strapping | spi | |
| 16 | 43 | TXD43PWM | strapping | uart | |
| 17 | 44 | RXD44PWM | strapping | uart | |
| 18 | 48 | RGB_DATA | strapping | - |
Start with these
6 pins with no boot or system involvementVBAT_VOLTAGEPWMA4D4SSA5A6D6A7D7A8D8
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 |
|---|---|---|---|
| A3 | 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 |
| SCK | 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 |
| 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 |
|---|---|---|---|
| A9 | 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 |
| A10 | FSPICS0 | Used to select the external flash chip. It is required for flash access and cannot be repurposed without losing flash connectivity | Flash |
| RGB_PWR | 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 |
| SCL | 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 |
| SDA | 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 |
| MISO | FSPIWP | On flash-equipped chips, this pin is tied to the flash’s WP# (or D3) line. It should be avoided for other use, as it’s needed for flash operations. | Flash |
| RGB_DATA | SPICLK_N | Used only on variants with Octal SPI interface, as the negative leg of the differential clock&. On such chips it operates at 1.8 V; it should be avoided for GPIO to prevent conflicts with the octal flash/PSRAM clock. | 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 18 pins on the Bee S3 are usable GPIO. Peripheral wiring is straightforward: I²C is mapped to SDA on GPIO37 and SCL on GPIO36; the SPI bus ( MOSI , MISO ,…
All 18 pins on the Bee S3 are usable GPIO.
Peripheral wiring is straightforward: I²C is mapped to SDA on GPIO37 and SCL on GPIO36; 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 8 ADC-capable pins for sensors and battery monitoring and 8 capacitive-touch inputs.
4 of the exposed pins carry boot-time or system duties on the ESP32-S3 (A3, SCK, TX and 1 more) - check the guidance above before wiring anything to them. VBAT_VOLTAGE, A4, SS, A6 and 2 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 - 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: Bee S3
USB CDC On Boot: Enabled
Flash Size: 8MB · DIO
Upload Speed: 921600
// blink
pinMode(1, OUTPUT);
digitalWrite(1, LOW); // on (often inverted)[env:Bee_S3]
platform = espressif32
board = esp32-s3-devkitc-1
framework = arduino
monitor_speed = 115200
upload_speed = 921600esp32:
board: esp32-s3-devkitc-1
variant: Bee_S3
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-S3Compute
MCU
ESP32-S3
Clock
240 MHz
SRAM · Flash
512 KB · 8MB
Radio
Wi-Fi
802.11 b/g/n
Bluetooth
5.0 LE
Antenna
PCB
I/O
GPIO · ADC
18 · 8
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
The Bee S3 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 $10.00 it's cheaper than most ESP32-S3 boards, which usually run around $30.
Around the module: an addressable RGB LED (GPIO48) and Reset/Boot buttons.
It flashes over native USB - no serial-converter driver needed, which isn't a given among ESP32-S3 boards.
- 1S LiPo battery connector with onboard battery-voltage monitoring on GPIO1
- No onboard LiPo charger by design, to minimise deep-sleep quiescent current
- Deep-sleep current below 20µA
- Built on the ESP32-S3-MINI-1 module (no PSRAM)
Where to buy
prices are typical street pricesBee S3
$10.00per unit, typical
Resources
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