How to Connect a DS1820 One‑Wire Temperature Sensor to a Raspberry Pi Using GPIO

Monitoring indoor or outdoor temperature with a Raspberry Pi can be done with a minimal setup. This guide shows how to wire a DS18S20 (DS1820) 1‑Wire sensor directly to a GPIO pin, read temperatures in software, and log the data with RRDtool.

Raspberry Pi and 1‑Wire

The DS18S20, DS18B20, and DS1822 are all 1‑Wire temperature sensors that fit in a TO‑92 package and combine a sensor, ADC, and serial interface. While they share the same pinout and software interface, they differ in cost and accuracy – the DS18S20 offers ±0.5 °C accuracy, the DS18B20 ±0.5 °C, and the DS1822 ±0.5 °C as well, but the latter is cheaper.

Each device has three pins: Ground (GND, pin 1), Data (DQ, pin 2), and Power (V_DD, pin 3). A parasitic power supply (3–5 V) allows the sensor to be powered solely from the data line using a pull‑up resistor.

Only One Resistor

Connect the sensor’s DQ pin to GPIO 4 on the Pi. Tie GND to the Pi’s ground and V_DD to GND, enabling parasitic power. Place a 4.7 kΩ pull‑up between 3.3 V and GPIO 4. The small breadboard or a right‑angle header keeps the wiring tidy and fits within the Pi’s official case.

1‑Wire Software Drivers

On Raspbian (or any Debian‑based distro) load the kernel modules with:

sudo modprobe w1-gpio pullup=1
sudo modprobe w1-therm

The pullup=1 flag tells the driver that the sensor is powered through the pull‑up resistor. After loading, each sensor appears as a subdirectory under /sys/bus/w1/devices. The directory name consists of the family code and the sensor’s unique 64‑bit identifier: DS18S20/DS1820 use family code 10, DS18B20 uses 28, and DS1822 uses 22.

Inside each directory is w1_slave, which contains two lines. The first shows the raw register dump and a CRC check. The second ends with t=xxxx, the temperature in millidegrees Celsius. Example:

cd /sys/bus/w1/devices
cd 10-000801b5*
cat w1_slave
0f 00 4b 46 ff ff 06 10 0c : crc=0c YES
0f 00 4b 46 ff ff 06 10 0c t=7375

The value 7375 corresponds to 7.375 °C. Note that the datasheet specifies an accuracy of ±0.5 °C, so the true temperature is within ±0.5 °C of the reading.

To ensure the modules load at boot, add them to /etc/modules:

# /etc/modules
w1-gpio pullup=1
w1-therm

Round‑Robin Database (RRDtool)

For long‑term storage and visualisation, RRDtool is ideal. Install it with:

sudo apt-get install rrdtool python-rrdtool

Define a database that records a value every 15 minutes and keeps daily aggregates for ten years:

rrdtool create temperature.rrd --step 900 \
DS:temp0:GAUGE:1200:-40:80 \
DS:temp1:GAUGE:1200:-40:80 \
RRA:AVERAGE:0.5:1:960 \
RRA:MIN:0.5:96:3600 \
RRA:MAX:0.5:96:3600 \
RRA:AVERAGE:0.5:96:3600

Data Acquisition with Python

Below is a minimal Python script that reads w1_slave and inserts the value into the RRDtool database. Adjust the sensor paths and database file name as needed.

import os
import rrdtool

W1_PATH = '/sys/bus/w1/devices'
DB_FILE = 'temperature.rrd'

def read_temp(sensor_id):
    with open(f'{W1_PATH}/{sensor_id}/w1_slave') as f:
        lines = f.readlines()
    if lines[1].strip().endswith('YES'):
        temp_milli = int(lines[1].strip().split('t=')[-1])
        return temp_milli / 1000.0
    return None

# Example for two sensors
temps = {
    'temp0': read_temp('10-000801b5'),
    'temp1': read_temp('28-0000045e')
}

rrdtool.update(DB_FILE, ','.join(str(t) for t in temps.values()))

Run the script periodically (e.g., via cron) to keep the database updated.