ESP32 HW-394 (WR-32)
Compact ESP32 development board with TYPE-C interface, WiFi, Bluetooth, and 4MB flash.
ESP32 HW-394 (WR-32) Pinout
31 pins
| Pin | GPIO | Labels | Status | Capabilities | Notes |
|---|---|---|---|---|---|
| 1 | - | EN | control | - | Chip enable / reset (active LOW) - the same net as the EN button |
| 2 | 36 | IO36GPIO36VPSVP | strapping | adc | SENSOR_VP, ADC1_CH0 - input only, no internal pull-ups |
| 3 | 39 | IO39GPIO39VNSVN | strapping | adc | SENSOR_VN, ADC1_CH3 - input only, no internal pull-ups |
| 4 | 34 | IO34GPIO34D34 | strapping | adc | ADC1_CH6 - input only, no internal pull-ups |
| 5 | 35 | IO35GPIO35D35 | strapping | adc | ADC1_CH7 - input only, no internal pull-ups |
| 6 | 32 | IO32GPIO32D32 | safe | adc · touch | ADC1_CH4, Touch9 (32 kHz crystal pad, unused on this board) |
| 7 | 33 | IO33GPIO33D33 | safe | adc · touch | ADC1_CH5, Touch8 (32 kHz crystal pad, unused on this board) |
| 8 | 25 | IO25GPIO25D25 | safe | adc · dac | DAC1, ADC2_CH8 |
| 9 | 26 | IO26GPIO26D26 | safe | adc · dac | DAC2, ADC2_CH9 |
| 10 | 27 | IO27GPIO27D27 | safe | adc · touch | ADC2_CH7, Touch7 |
| 11 | 14 | IO14GPIO14D14 | strapping | adc · touch · spi | ADC2_CH6, Touch6, HSPI CLK |
| 12 | 12 | IO12GPIO12D12 | strapping | adc · touch · spi | ADC2_CH5, Touch5, HSPI MISO, strapping pin (flash voltage) - must not be high at boot |
| 13 | 13 | IO13GPIO13D13 | strapping | adc · touch · spi | ADC2_CH4, Touch4, HSPI MOSI |
| 14 | - | GND | ground | - | Ground |
| 15 | - | VIN5V | power | - | 5V input to the AMS1117 regulator (also 5V from USB-C when powered over USB) |
| 16 | 23 | IO23GPIO23D23 | safe | spi | VSPI MOSI (default SPI) |
| 17 | 22 | IO22GPIO22D22SCL | safe | i2c | I2C SCL (default) |
| 18 | 1 | IO1GPIO1TX0TXD0 | uart | uart | UART0 TX - wired to the CH340C USB serial chip, avoid for general IO |
| 19 | 3 | IO3GPIO3RX0RXD0 | uart | uart | UART0 RX - wired to the CH340C USB serial chip, avoid for general IO |
| 20 | 21 | IO21GPIO21D21SDA | safe | i2c | I2C SDA (default) |
| 21 | 19 | IO19GPIO19D19 | safe | spi | VSPI MISO (default SPI) |
| 22 | 18 | IO18GPIO18D18 | safe | spi | VSPI SCK (default SPI) |
| 23 | 5 | IO5GPIO5D5 | strapping | spi | VSPI CS (default SPI), strapping pin - outputs a PWM burst at boot |
| 24 | 17 | IO17GPIO17D17TX2 | safe | - | UART2 TX (default Serial2 pin in older Arduino cores) |
| 25 | 16 | IO16GPIO16D16RX2 | safe | - | UART2 RX (default Serial2 pin in older Arduino cores) |
| 26 | 4 | IO4GPIO4D4 | safe | adc · touch | ADC2_CH0, Touch0 |
| 27 | 2 | IO2GPIO2D2 | strapping | adc · touch | ADC2_CH2, Touch2, on-board blue LED (silk D2), strapping pin - keep floating or low at boot |
| 28 | 15 | IO15GPIO15D15 | strapping | adc · touch · spi | ADC2_CH3, Touch3, HSPI CS, strapping pin - pull low at boot to silence ROM boot messages |
| 29 | - | GND | ground | - | Ground |
| 30 | - | 3V33.3V | power | - | 3.3V output from the AMS1117 regulator |
| 31 | 0 | IO0GPIO0 | strapping | - | Not on the header - wired to the BOOT button; hold it at reset for download mode (strapping pin) |
Start with these
13 pins with no boot or system involvementFreely assignable - no strapping, flash, USB or JTAG duties. Ideal first picks for buttons, sensors and LEDs.
Fine - with a little care
13 pins · 12 things to knowIO36 Input-only GPIO (no output); ADC1 channel 0, Hall sensor VP. Other
Cannot be used as output; only suitable for input (e.g., analog read).
IO39IO35 Input-only GPIOs with ADC1 channels - no output driver Other
Cannot be used as output; only suitable for input.
- IO39Input-only GPIO (no output); ADC1 channel 3, Hall sensor VN.
- IO35Input-only GPIO (no output driver); ADC1 channel 7.
IO34 Input-only GPIO (no output driver); ADC1 channel 6. Other
Cannot be used as output (no drive capability); only suitable for analog/digital input.
IO14 JTAG mode select pin (TMS); also HSPI CLK and PWM-capable GPIO. JTAG
Used for JTAG debugging (TMS); driving it as GPIO may interfere with JTAG or produce spurious signals at boot.
IO12 Bootstrapping pin; JTAG TDI; sets flash voltage (VDD_SDIO); also HSPIQ (flash data line). Strapping
Keep LOW during boot (internal PD); pulling HIGH at reset selects 1.8V flash mode, causing flash brownout if 3.3V flash is used.
IO13 JTAG clock pin (TCK); also ADC2 channel 4 / Touch4 input. JTAG
Used for JTAG debugging (TCK); avoid using as GPIO if JTAG is needed.
IO1 Default UART0 TX pin for USB-serial programming and console. UART
Connected to on-board USB-UART for uploading and logs; drives serial output at boot, so using as GPIO can disrupt programming or console.
IO3 Default UART0 RX pin for USB-serial programming (console input). UART
Used for receiving data from USB-UART (programming); also pulled HIGH at boot for console communication, so using as GPIO can disrupt uploads.
IO5 Bootstrapping pin; internal pull-up; VSPI CS0 (default SPI chip-select); acts as FSPIWP (flash write-protect) on internal-flash variants. Strapping
Must be HIGH during boot; if pulled LOW at reset, alters SDIO slave timing and may prevent normal boot.
IO2 Bootstrapping pin (must be low or floating at reset); internal pull-down. Strapping
If driven HIGH on reset (while IO0 is LOW), selects an unsupported SDIO boot mode, causing boot failure.
IO15 Bootstrapping pin; JTAG TDO; controls UART0 boot log output; also HSPICS0 (secondary SPI CS). Strapping
Keep HIGH during boot (internal PU); if LOW on reset, bootloader log is silenced and boot mode may change.
IO0 Bootstrapping pin (enter bootloader when low); internal pull-up. Strapping
Must be HIGH during boot for normal startup; if held LOW on reset, forces flash programming mode.
Across 31 pins, the ESP32 HW-394 (WR-32) exposes 26 GPIO plus GND, VIN and 3V3 for power.
For peripherals, I²C is mapped to SDA on GPIO21 and SCL on GPIO22.
On the analog side there are 15 ADC-capable pins for sensors and battery monitoring, 9 capacitive-touch inputs and 2 true DAC outputs.
If you want zero surprises, IO32, IO33, IO25, IO26 and 9 more are free of any such role - the safest first picks. 13 of the exposed pins carry boot-time or system duties on the ESP32 (IO36, IO39, IO34 and 10 more).
Getting started
flash your first firmware in ~2 minutesBoard: 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
// toggle GPIO32 - wire an LED and resistor to it
void setup() {
pinMode(32, OUTPUT);
}
void loop() {
digitalWrite(32, HIGH); delay(500);
digitalWrite(32, LOW); delay(500);
}[env:esp32-hw-394]
platform = espressif32
board = esp32dev
framework = arduino
monitor_speed = 115200
upload_speed = 921600esp32dev - or type it after board =.esp32:
board: esp32dev
variant: esp32
framework:
type: esp-idf
# blink - GPIO32
output:
- platform: gpio
pin: 32
id: led_out
light:
- platform: binary
name: "LED"
output: led_outesp32dev (same ids as PlatformIO).esptool.py --chip esp32 --port /dev/ttyACM0 \
--baud 921600 write_flash 0x1000 firmware.bin--port = your /dev/tty* (macOS/Linux) or COMx (Windows).Good to know
board-specific quirks worth 60 seconds
ESP32 HW-394 Variants Different Models Flash Memory: Typically 4MB, but check specifications as some variants might differ. Board Layout: Slight differences in component placement or additional features like onboard LEDs. Compatibility Notes All variants are based on the ESP32 WROOM-32 module and should be compatible with standard ESP32 development tools. Always verify the pinout and specifications for your specific…
ESP32 HW-394 Variants
Different Models
- Flash Memory: Typically 4MB, but check specifications as some variants might differ.
- Board Layout: Slight differences in component placement or additional features like onboard LEDs.
Compatibility Notes
All variants are based on the ESP32 WROOM-32 module and should be compatible with standard ESP32 development tools. Always verify the pinout and specifications for your specific board version.
Choosing the Right Variant
Look for boards with reliable USB chips and sufficient flash memory for your project needs. The HW-394 is a cost-effective option for ESP32 prototyping.
Downloads
Free for non-commercial use, credit espboards.dev · License
Board illustration
The bare ESP32 HW-394 (WR-32) board drawn to scale, with no pin labels on it. Made for slide decks, wiring diagrams and project write-ups where a photo is too busy. Take the scalable SVG for print or editing, the high-resolution PNG to drop straight in, or the transparent PNG when you need it with no background behind it.
Pinout diagram
Every pin on both sides of the board with its functions, drawn by ESPboards from the ESP32 Series Datasheet v5.3 - the same sheet shown at the top of this page. The PNG is a high-resolution image for screens, the SVG is vector so it stays sharp at any size, and the PDF is laid out to print on A4 or Letter.
Yours to use, share and adapt for non-commercial work, as long as you credit espboards.dev - the full terms and ready-made credit lines are here.
Specifications
ESP32 · vs other ESP32 chips →About this board
At its core is the ESP32 - a dual-core Xtensa with both Bluetooth Classic and BLE.
Expect to pay about $5.00 - less than the ~$20 most ESP32 boards go for.
Onboard you'll find EN/Boot buttons.
Where to buy
prices are typical street pricesResources
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