Hornbill ESP32 Minima

Slimmed-down ESP32 board with basic I/O - great for embedding into finished products or compact devices.

Hornbill ESP32 Minima board
ESP32
MCU
240MHz
clock
4MB
flash
520KB
SRAM
16· 7 ADC
GPIO
BLE 4.2+ WiFi
radio
On this page

Pinout

16 pins
View:
PinGPIOLabelsStatusCapabilitiesNotes
10A11T1strappingadc · touch
21TXPWMuartuart
32SSA12T2PWMstrappingadc · touch · spi
43RXPWMuartuart
54A10T0PWMstrappingadc · touch
613A14PWMstrappingadc
715A13T3PWMstrappingadc · touch
818SCKPWMsafespi
919MISOPWMsafespi
1021SDAPWMsafei2c
1122SCLPWMsafei2c
1223MOSIPWMsafespi
1325DAC1PWMsafedac
1426DAC2PWMsafedac
1534A6strappingadc
1635A7strappingadc

Start with these

7 pins with no boot or system involvement
SCKPWMMISOPWMSDAPWMSCLPWMMOSIPWMDAC1PWMDAC2PWM

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
PinLabelWhat to knowRole
A11GPIO0Must be HIGH during boot for normal startup; if held LOW on reset, forces flash programming mode.Strapping
SSGPIO2If driven HIGH on reset (while IO0 is LOW), selects an unsupported SDIO boot mode, causing boot failure.Strapping
A10GPIO4Sampled at reset for boot config; should not be driven at boot (affects boot mode timing).Strapping
A14MTCK (GPIO13)Used for JTAG debugging (TCK); avoid using as GPIO if JTAG is needed.Other
A13MTDO (GPIO15)Keep HIGH during boot (internal PU); if LOW on reset, bootloader log is silenced and boot mode may change.Strapping
A6GPIO34Cannot be used as output (no drive capability); only suitable for analog/digital input.Other
A7GPIO35Cannot be used as output; only suitable for input.Other

Only if you know the tricks

wired to flash or USB - expect a fight
PinLabelWhat to knowRole
TXU0TXD (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
RXU0RXD (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
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 Hornbill ESP32 Minima pinout brings out 16 GPIO pins - every one of them usable in your project. For peripherals, I²C is mapped to SDA on GPIO21 and SCL on…

The Hornbill ESP32 Minima pinout brings out 16 GPIO pins - 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 GPIO1 and GPIO3 cover serial logging and flashing.

On the analog side there are 7 ADC-capable pins for sensors and battery monitoring, 4 capacitive-touch inputs and 2 true DAC outputs.

If you want zero surprises, SCK, MISO, SDA, SCL and 3 more are free of any such role - the safest first picks. 7 of the exposed pins carry boot-time or system duties on the ESP32 (A11, SS, A10 and 4 more).

Getting started

flash your first firmware in ~2 minutes
Tool:
1
Connect over USB
Install your USB-serial driver (CH340 / CP210x) if no port appears. Not detected? Hold BOOT while plugging in.
2
Match & flash
Set the Tools options shown, then click Upload.
3
Verify it runs
The onboard LED on GPIO18 blinks - swap the pin if your board's LED differs.
Set these in Tools · leave everything else at default
Arduino IDE 2.x — Tools Copy
Board: "ESP32 Dev Module"
Flash Size: "4MB (32Mb)"
Flash Mode: "DIO"
Partition Scheme: "Default 4MB with spiffs (1.2MB APP / 1.5MB SPIFFS)" (default)
Upload Speed: "921600"
▸ every other Tools option — leave at default
Board: 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
Find it: Tools ▸ Board ▸ ESP32 Arduino ▸ ESP32 Dev Module
blink.ino Copy
// blink the onboard LED
void setup() {
  pinMode(18, OUTPUT);
}
void loop() {
  digitalWrite(18, HIGH); delay(500);
  digitalWrite(18, LOW);  delay(500);
}
board to selectesp32dev⧉ copy
platformio.ini Copy
[env:hornbill32minima]
platform = espressif32
board = esp32dev
framework = arduino
monitor_speed = 115200
upload_speed = 921600
Find it: PlatformIO Home ▸ Boards, search esp32dev — or type it after board =.
board to selectesp32dev⧉ copy
device.yaml Copy
esp32:
  board: esp32dev
  variant: hornbill32minima
  framework:
    type: esp-idf

# blink - GPIO18
output:
  - platform: gpio
    pin: 18
    id: led_out
light:
  - platform: binary
    name: "LED"
    output: led_out
Find it: search ESPHome's board list for esp32dev (same ids as PlatformIO).
esptool doesn't pick board settings — a prebuilt .bin already has them baked in. This is just the raw flash command.
terminal Copy
esptool.py --chip esp32 --port /dev/ttyACM0 \
  --baud 921600 write_flash 0x0 firmware.bin
--port = your /dev/tty* (macOS/Linux) or COMx (Windows).
Build details: sketch space 1310720 B · data 327680 B · DIO

Specifications

ESP32
Compute
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
16 · 7
UART · I²C · SPI
3 · 2 · 4
PWM
16 channels
Power
USB
None
Serial
-
Boot address
0x1000
Flashing
Upload · OTA
esptool_py · esp_ota
Flash · Boot mode
DIO · DIO
Sketch · Data
1.25 MB · 320 KB
The Hornbill ESP32 Minima 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 $12.00 - less than the ~$20 most ESP32 boards go for.

Only 16 GPIO are broken out, where most ESP32 boards manage about 24 - worth checking the pinout covers what you need.

Onboard you'll find battery charging via true, status LEDs (Power, RGB) and Reset buttons.

  • Round wearable form factor with large crocodile-clip I/O pads
  • No onboard USB - flashed via a 6-pin header with an external USB-to-serial adapter
  • Onboard 32.768 kHz crystal for RTC and accurate deep-sleep timing

Where to buy

prices are typical street prices
Hornbill ESP32 Minima
Hornbill ESP32 Minima
$12.00per unit, typical

Resources

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