boneIO Edge Temp

SHT40 temperature & humidity sensor on ATtiny402 with Modbus RTU over RS-485.

Register Map

Addr	Name	Unit	R/W	Description
0	Humidity	0.1 %RH	R	Humidity (S_WORD, × 0.1 = %)
1	Temperature	0.1 °C	R	Temperature (S_WORD, × 0.1 = °C)
100	Slave ID	1–247	R/W	Modbus address
101	Baud Rate	0–3	R/W	0=2400, 1=4800, 2=9600, 3=19200
102	LED mode	0–2	R/W	0=off, 1=on, 2=auto
103	FW version	—	R	e.g. 0x0001 = v0.1
104	Temp cal	0.1 °C	R/W	Temperature calibration offset (±50)
105	Hum cal	0.1 %RH	R/W	Humidity calibration offset (±50)

Defaults: address 1, baud 9600, LED auto.

Build

Requirements

• avr-gcc + avr-libc
• pymcuprog or avrdude ≥ 7.x (for UPDI flashing)

Linux (Ubuntu/Debian)

# One-command install (gcc-avr + avr-libc + ATtiny402 DFP + pymcuprog)
./setup_toolchain.sh

make            # compile
make size       # check size (max 4KB flash / 256B RAM)
make flash      # erase + write + verify via UPDI

Flashing via UPDI

Connect a UPDI programmer (e.g. UPDI Friend, SerialUPDI) to UPDI pin (PA0) on header H1.

⚠️ Remove R20 (470Ω) from the UPDI line and replace with a solder bridge — the UPDI Friend already has its own resistor.

Linux (default port /dev/ttyUSB1):

pymcuprog write -t uart -u /dev/ttyUSB1 -d attiny402 -f sht40_modbus.hex --erase --verify

Windows — no compiler needed, just flash the .hex from GitHub Releases:

# Install pymcuprog (requires Python 3)
pip install pymcuprog

# Flash (replace COM3 with your port from Device Manager)
pymcuprog write -t uart -u COM3 -d attiny402 -f boneio-edge-temp-v0.1.hex --erase --verify

💡 Find your COM port in Device Manager → Ports (COM & LPT) after plugging in the UPDI programmer.

VSCode

1. Install PlatformIO or AVR Helper extension.
2. Open this folder in VSCode.
3. Terminal → New Terminal:

   make          # build
   make flash    # flash

CI/CD

GitHub Action builds firmware automatically on every push.

To create a Release with binary:

git tag v0.1
git push --tags

The .hex binary will appear under Releases on GitHub.

Hardware

• MCU: ATtiny402-SSFR (3.3V, 8-pin)
• Sensor: SHT40-AD1B-R3 (I2C, address 0x44)
• RS-485: THVD1406DR (auto-direction, no DE/RE)
• LED: NCD0402G1 (active low on PA3)

ATtiny402 Pinout

Pin	Function
PA0	UPDI
PA1	SDA (I2C → SHT40)
PA2	SCL (I2C → SHT40)
PA3	LED
PA6	TXD (UART → RS-485)
PA7	RXD (UART ← RS-485)

License

GPL-3.0 — Copyright (C) 2025 boneIO Sp. z o.o. Made in Poland.

See LICENSE.

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🇵🇱 Dokumentacja po polsku

Mapa rejestrów

Adres	Nazwa	Jednostka	R/W	Opis
0	Humidity	0.1 %RH	R	Wilgotność (S_WORD, × 0.1 = %)
1	Temperature	0.1 °C	R	Temperatura (S_WORD, × 0.1 = °C)
100	Slave ID	1–247	R/W	Adres Modbus
101	Baud Rate	0–3	R/W	0=2400, 1=4800, 2=9600, 3=19200
102	LED mode	0–2	R/W	0=off, 1=on, 2=auto
103	FW version	—	R	Np. 0x0001 = v0.1
104	Temp cal	0.1 °C	R/W	Offset kalibracji temp (±50.0)
105	Hum cal	0.1 %RH	R/W	Offset kalibracji wilg. (±50.0)

Domyślnie: adres 1, baudrate 9600, LED auto.

Kompilacja i flashowanie

# Instalacja toolchaina
sudo apt install gcc-avr avr-libc
pip install pymcuprog

# Kompilacja
make

# Sprawdzenie rozmiaru (max 4KB flash / 256B RAM)
make size

# Flashowanie przez UPDI (erase + write + verify)
make flash

⚠️ Usuń rezystor R20 (470Ω) z linii UPDI i zastąp zworką.

CI/CD

GitHub Action buduje firmware automatycznie. Aby stworzyć Release z binarką:

git tag v0.1
git push --tags

Licencja

GPL-3.0 — Copyright (C) 2025 boneIO Sp. z o.o. Made in Poland.