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ESP32 HW-394 (WR-32)
Compact ESP32 development board with TYPE-C interface, WiFi, Bluetooth, and 4MB flash.
ESP32
MCU
240MHz
clock
4MB
flash
520KB
SRAM
24· 9 ADC
GPIO
BLE 4.2+ WiFi
radio
Pinout
24 pins
| Pin | GPIO | Labels | Status | Capabilities | Notes |
|---|---|---|---|---|---|
| 1 | 0 | IO0GPIO0 | strapping | - | GPIO0, Boot Mode Selection |
| 2 | 2 | IO2GPIO2 | strapping | - | GPIO2, General Purpose I/O |
| 3 | 4 | IO4GPIO4 | strapping | - | GPIO4, General Purpose I/O |
| 4 | 5 | IO5GPIO5 | strapping | - | GPIO5, General Purpose I/O |
| 5 | 12 | IO12GPIO12 | strapping | adc | GPIO12, ADC or GPIO |
| 6 | 13 | IO13GPIO13 | strapping | adc | GPIO13, ADC or GPIO |
| 7 | 14 | IO14GPIO14 | strapping | adc | GPIO14, ADC or GPIO |
| 8 | 15 | IO15GPIO15 | strapping | adc | GPIO15, ADC or GPIO |
| 9 | 16 | IO16GPIO16 | strapping | - | GPIO16, General Purpose I/O |
| 10 | 3 | RXGPIO3 | uart | uart | UART0 Receive |
| 11 | 1 | TXGPIO1 | uart | uart | UART0 Transmit |
| 12 | 17 | IO17GPIO17 | strapping | - | GPIO17, General Purpose I/O |
| 13 | 18 | IO18GPIO18 | safe | - | GPIO18, General Purpose I/O |
| 14 | 19 | IO19GPIO19 | safe | - | GPIO19, General Purpose I/O |
| 15 | 21 | IO21GPIO21 | safe | i2c | GPIO21, I2C SDA |
| 16 | 22 | IO22GPIO22 | safe | i2c | GPIO22, I2C SCL |
| 17 | 23 | IO23GPIO23 | safe | spi | GPIO23, SPI MOSI |
| 18 | 25 | IO25GPIO25 | safe | dac | GPIO25, DAC1 |
| 19 | 26 | IO26GPIO26 | safe | dac | GPIO26, DAC2 |
| 20 | 27 | IO27GPIO27 | safe | adc | GPIO27, ADC |
| 21 | 32 | IO32GPIO32 | safe | adc | GPIO32, ADC |
| 22 | 33 | IO33GPIO33 | safe | adc | GPIO33, ADC |
| 23 | 34 | IO34GPIO34 | strapping | adc | GPIO34, ADC Input Only |
| 24 | 35 | IO35GPIO35 | strapping | adc | GPIO35, ADC Input Only |
Start with these
10 pins with no boot or system involvementIO18GPIO18IO19GPIO19IO21GPIO21IO22GPIO22IO23GPIO23IO25GPIO25IO26GPIO26IO27GPIO27IO32GPIO32IO33GPIO33
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 |
|---|---|---|---|
| IO0 | GPIO0 | Must be HIGH during boot for normal startup; if held LOW on reset, forces flash programming mode. | Strapping |
| IO2 | GPIO2 | If driven HIGH on reset (while IO0 is LOW), selects an unsupported SDIO boot mode, causing boot failure. | Strapping |
| IO4 | GPIO4 | Sampled at reset for boot config; should not be driven at boot (affects boot mode timing). | Strapping |
| IO5 | GPIO5 | Must be HIGH during boot; if pulled LOW at reset, alters SDIO slave timing and may prevent normal boot. | Strapping |
| IO12 | MTDI (GPIO12) | Keep LOW during boot (internal PD); pulling HIGH at reset selects 1.8V flash mode, causing flash brownout if 3.3V flash is used. | Strapping |
| IO13 | MTCK (GPIO13) | Used for JTAG debugging (TCK); avoid using as GPIO if JTAG is needed. | Other |
| IO14 | MTMS (GPIO14) | Used for JTAG debugging (TMS); driving it as GPIO may interfere with JTAG or produce spurious signals at boot. | Other |
| IO15 | MTDO (GPIO15) | Keep HIGH during boot (internal PU); if LOW on reset, bootloader log is silenced and boot mode may change. | Strapping |
| IO34 | GPIO34 | Cannot be used as output (no drive capability); only suitable for analog/digital input. | Other |
| IO35 | GPIO35 | Cannot be used as output; only suitable for input. | Other |
Only if you know the tricks
wired to flash or USB - expect a fight| Pin | Label | What to know | Role |
|---|---|---|---|
| IO16 | GPIO16 | Connected to internal PSRAM on PSRAM-enabled modules; not usable as GPIO on those modules. | Flash |
| RX | U0RXD (GPIO3) | Used for receiving data from USB-UART (programming); also pulled HIGH at boot for console communication, so using as GPIO can disrupt uploads. | USB |
| TX | U0TXD (GPIO1) | Connected to on-board USB-UART for uploading and logs; drives serial output at boot, so using as GPIO can disrupt programming or console. | USB |
| IO17 | GPIO17 | Connected to internal PSRAM on PSRAM-enabled modules; not usable as GPIO on those modules. | 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 ESP32 HW-394 (WR-32) pinout brings out 24 GPIO pins - every one of them usable in your project. For peripherals, TX / RX on GPIO1 and GPIO3 cover serial…
The ESP32 HW-394 (WR-32) pinout brings out 24 GPIO pins - every one of them usable in your project.
For peripherals, TX/RX on GPIO1 and GPIO3 cover serial logging and flashing.
On the analog side there are 9 ADC-capable pins for sensors and battery monitoring and 2 true DAC outputs.
If you want zero surprises, IO18, IO19, IO21, IO22 and 6 more are free of any such role - the safest first picks. 10 of the exposed pins carry boot-time or system duties on the ESP32 (IO0, IO2, IO4 and 7 more).
Getting started
flash your first firmware in ~2 minutes1
Connect over USB
Serial chip: CH340. 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 GPIO18 - swap for your board's LED pin if different.
Board: Esp32 Hw 394
Flash Size: 4MB · DIO
Upload Speed: 921600
// blink
pinMode(18, OUTPUT);
digitalWrite(18, LOW); // on (often inverted)[env:esp32-hw-394]
platform = espressif32
board = esp32dev
framework = arduino
monitor_speed = 115200
upload_speed = 921600esp32:
board: esp32dev
variant: esp32
framework:
type: esp-idf
# blink - GPIO18
output:
- platform: gpio
pin: 18
id: led_out
light:
- platform: binary
name: "LED"
output: led_outesptool.py --chip esp32 --port /dev/ttyACM0 \
write_flash 0x0 firmware.binBuild details: sketch space 1310720 B · data 327680 B · DIO
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.
Specifications
ESP32Compute
MCU
ESP32
Clock
240 MHz
SRAM · Flash
520 KB · 4MB
Radio
Wi-Fi
802.11 b/g/n
Bluetooth
4.2 LE
Antenna
PCB
I/O
GPIO · ADC
24 · 9
UART · I²C · SPI
3 · 2 · 4
PWM
16 channels
Power
USB
USB-C
Serial
CH340
Boot address
0x1000
Flashing
Upload · OTA
esptool_py · esp_ota
Flash · Boot mode
DIO · DIO
Sketch · Data
1.25 MB · 320 KB
The ESP32 HW-394 (WR-32) uses esptool_py for firmware uploads, esp_ota for over-the-air (OTA) updates. Flash mode is DIO with DIO 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 - 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 prices
Resources
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