1-Wire Interface (One-Wire Bus)

1-Wire is a simple communication protocol developed by Maxim Integrated (Dallas Semiconductor) that allows data and power to be delivered over a single data wire plus ground. It is commonly used for low-speed sensors such as temperature probes.

Typical devices include: - DS18B20 temperature sensors
- iButton devices
- EEPROM identification chips

Enabling 1-Wire on Raspberry Pi

• raspi-config → Interface Options → One Wire

Raspberry Pi provides built-in support for 1-Wire using a kernel driver.

Enable via /boot/config.txt

Edit the configuration file:

sudo nano /boot/config.txt

Add the following line:

dtoverlay=w1-gpio

By default this uses: - GPIO4 (Pin 7) as the data pin

You can specify a different pin if required:

dtoverlay=w1-gpio,gpiopin=17

Reboot the Pi:

sudo reboot

How 1-Wire Works

The bus uses: - DQ (Data line) – carries both data and timing signals
- GND (Ground)
- Optional VCC (3.3 V or 5 V) if not using parasitic power

All devices share the same data line and are identified by a unique 64-bit ID, allowing many devices to exist on the same bus.

Power Modes

1-Wire devices can operate in two ways:

Mode	Description
Normal power	Device uses VCC, GND, and DATA
Parasitic power	Device steals power from the data line (DATA + GND only)

For reliability, normal powered mode is recommended instead of parasitic power.

Verifying 1-Wire is Working

After reboot, check that the driver is loaded:

ls /sys/bus/w1/devices/

You should see folders like:

28-00000abcdef0
w1_bus_master1

Each 28-xxxxxxxxxxxx folder represents a detected 1-Wire device.

Reading a DS18B20 Temperature Sensor

You can read the temperature directly from the system:

cat /sys/bus/w1/devices/28-xxxxxxxxxxxx/w1_slave

Example output:

aa 01 4b 46 7f ff 0c 10 5e : crc=5e YES
aa 01 4b 46 7f ff 0c 10 5e t=26000

The temperature is reported as: - t=26000 → 26.000°C