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Heltec WiFi Kit 32(V3)
An ESP32-S3 board with an integrated 0.96" OLED display, designed for compact, battery-powered IoT and wireless projects.
50.2 × 25.5 mm
ESP32-S3
MCU
240MHz
clock
8MB
flash
512KB
SRAM
27· 20 ADC
GPIO
BLE 5.0+ WiFi
radio
Pinout
27 pins · 2.54 mm pitch
| Pin | GPIO | Labels | Status | Capabilities | Notes |
|---|---|---|---|---|---|
| 1 | 0 | KEY_BUILTIN | strapping | - | |
| 2 | 1 | A0T1PWM | safe | adc · touch | |
| 3 | 2 | A1T2PWM | safe | adc · touch | |
| 4 | 3 | A2T3PWM | strapping | adc · touch | |
| 5 | 4 | A3T4PWM | safe | adc · touch | |
| 6 | 5 | A4T5PWM | safe | adc · touch | |
| 7 | 6 | A5T6PWM | safe | adc · touch | |
| 8 | 7 | A6T7PWM | safe | adc · touch | |
| 9 | 8 | SSA7T8PWM | safe | adc · touch · spi | |
| 10 | 9 | SCKA8T9PWM | strapping | adc · touch · spi | |
| 11 | 10 | MOSIA9T10PWM | strapping | adc · touch · spi | |
| 12 | 11 | MISOA10T11PWM | strapping | adc · touch · spi | |
| 13 | 12 | A11T12PWM | strapping | adc · touch | |
| 14 | 13 | A12T13PWM | strapping | adc · touch | |
| 15 | 14 | A13T14PWM | strapping | adc · touch | |
| 16 | 15 | A14PWM | safe | adc | |
| 17 | 16 | A15PWM | safe | adc | |
| 18 | 17 | A16SDA_OLEDPWM | safe | adc | |
| 19 | 18 | A17SCL_OLEDPWM | safe | adc | |
| 20 | 19 | A18PWM | uart | adc | |
| 21 | 20 | A19PWM | uart | adc | |
| 22 | 21 | SDARST_OLEDPWM | safe | i2c | |
| 23 | 22 | SCLPWM | safe | i2c | |
| 24 | 35 | LED_BUILTINLED | strapping | - | |
| 25 | 36 | Vext | strapping | - | |
| 26 | 43 | TX | strapping | uart | |
| 27 | 44 | RX | strapping | uart |
Start with these
13 pins with no boot or system involvementA0T1A1T2A3T4A4T5A5T6A6T7SSA7A14PWMA15PWMA16SDA_OLEDA17SCL_OLEDSDARST_OLEDSCLPWM
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 |
|---|---|---|---|
| KEY_BUILTIN | GPIO0 | Must be pulled high (default) or low (to enter UART download mode) at reset. Using it for other functions can interfere with boot mode configuration. | Strapping |
| 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 |
|---|---|---|---|
| SCK | 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 |
| MOSI | FSPICS0 | Used to select the external flash chip. It is required for flash access and cannot be repurposed without losing flash connectivity | Flash |
| MISO | 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 |
| A13 | FSPIWP | Connected to external flash (data/write-protect signal). Not recommended as GPIO because it’s reserved for flash operations. | Flash |
| A18 | USB_D- | By default connected to the on-chip USB Serial/JTAG controller. Using it as general GPIO without reconfiguring IO MUX will interfere with USB functionality. | USB |
| A19 | USB_D+ | By default connected to the on-chip USB Serial/JTAG controller. Using it as general GPIO without reconfiguring IO MUX will interfere with USB functionality. | USB |
| LED_BUILTIN | 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 |
| Vext | 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 |
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 Heltec WiFi Kit 32(V3) pinout brings out 27 GPIO pins at a 2.54 mm pitch - every one of them usable in your project. For peripherals, I²C is mapped to SDA…
The Heltec WiFi Kit 32(V3) pinout brings out 27 GPIO pins at a 2.54 mm pitch - every one of them usable in your project.
For peripherals, I²C is mapped to SDA on GPIO21 and SCL on GPIO22; 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 20 ADC-capable pins for sensors and battery monitoring and 14 capacitive-touch inputs.
If you want zero surprises, A0, A1, A3, A4 and 9 more are free of any such role - the safest first picks. 4 of the exposed pins carry boot-time or system duties on the ESP32-S3 (KEY_BUILTIN, A2, TX and 1 more).
Getting started
flash your first firmware in ~2 minutes1
Connect over USB
Serial chip: CP2102. 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: Heltec Wifi Kit 32 V3
Flash Size: 8MB · DIO
Upload Speed: 921600
// blink
pinMode(1, OUTPUT);
digitalWrite(1, LOW); // on (often inverted)[env:heltec_wifi_kit_32_V3]
platform = espressif32
board = esp32-s3-devkitc-1
framework = arduino
monitor_speed = 115200
upload_speed = 921600esp32:
board: esp32-s3-devkitc-1
variant: heltec_wifi_kit_32_V3
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 3342336 B · data 327680 B · DIO
Specifications
ESP32-S3 · 50.2 × 25.5 mmCompute
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
27 · 20
UART · I²C · SPI
3 · 2 · 4
PWM
8 channels
Power
USB
USB-C
Serial
CP2102
Boot address
0x0
Display
Screen
OLED · 0.96" · 128x64
Driver
SSD1306
Touch
No
Flashing
Upload · OTA
esptool_py · esp_ota
Flash · Boot mode
DIO · QIO
Sketch · Data
3.19 MB · 320 KB
50.2 × 25.5 mm · pin pitch 2.54 mm
The Heltec WiFi Kit 32(V3) 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 3.19 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 $12.99 - less than the ~$30 most ESP32-S3 boards go for.
27 GPIO are broken out - more than most ESP32-S3 boards, so the pin budget is rarely the constraint.
Onboard you'll find an OLED 0.96" 128x64 display, battery charging via JST-SH 1.25mm and Reset/PRG buttons.
- Vext pin (GPIO36) switches the 3.3V rail to the OLED & external sensors (350mA max)
- Onboard Li-Po charger with battery-voltage sensing via ADC on GPIO1 (VBAT)
Where to buy
prices are typical street pricesHeltec WiFi Kit 32(V3)
$12.99per unit, typical
Resources
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