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Lesson 18: Temperature Sensor Module (DS18B20)

In this lesson, you will learn how to use a Raspberry Pi to read temperature data from a DS18B20 temperature sensor. You will understand how to locate the sensor’s device file, read and parse its raw data, and convert this data into Celsius and Fahrenheit readings.

Required Components

In this project, we need the following components.

It’s definitely convenient to buy a whole kit, here’s the link:

Name	ITEMS IN THIS KIT	LINK
Universal Maker Sensor Kit	94	Universal Maker Sensor Kit

You can also buy them separately from the links below.

Component Introduction	Purchase Link
Raspberry Pi 5	BUY
Temperature Sensor Module (DS18B20)	-
Breadboard	BUY

Wiring

Code

Note

The DS18B20 module communicates with the Raspberry Pi using the onewire protocol. Before running the code, you need to enable the onewire function of the Raspberry Pi. You can refer to this tutorial: 1-Wire Configuration.

import glob
import time

# Path to the directory containing device files for 1-wire devices
base_dir = "/sys/bus/w1/devices/"

# Finds the first device folder that starts with "28", specific to DS18B20
device_folder = glob.glob(base_dir + "28*")[0]

# Device file containing the temperature data
device_file = device_folder + "/w1_slave"


def read_temp_raw():
    # Reads raw temperature data from the sensor
    f = open(device_file, "r")
    lines = f.readlines()
    f.close()
    return lines


def read_temp():
    # Parses the raw temperature data and converts it to Celsius and Fahrenheit
    lines = read_temp_raw()
    # Waits for a valid temperature reading
    while lines[0].strip()[-3:] != "YES":
        time.sleep(0.2)
        lines = read_temp_raw()
    equals_pos = lines[1].find("t=")
    if equals_pos != -1:
        temp_string = lines[1][equals_pos + 2 :]
        temp_c = float(temp_string) / 1000.0  # Convert to Celsius
        temp_f = temp_c * 9.0 / 5.0 + 32.0  # Convert to Fahrenheit
        return temp_c, temp_f


try:
    # Main loop to continuously read and print temperature
    while True:
        temp_c, temp_f = read_temp()
        formatted_output = f"Temperature: {temp_c:.2f}°C / {temp_f:.2f}°F"
        print(formatted_output)
        time.sleep(1)  # Wait for 1 second between readings
except KeyboardInterrupt:
    # Gracefully exit the program on CTRL+C
    print("Exit")

Code Analysis

Importing Necessary Libraries

The glob library is used to search for the temperature sensor’s device folder. The time library is used for implementing delays in the program.
```
import glob
import time
```
Locating the Temperature Sensor Device File

The code searches for the directory of the DS18B20 sensor by looking for a folder name starting with “28”. The device file w1_slave contains the temperature data.
```
base_dir = "/sys/bus/w1/devices/"
device_folder = glob.glob(base_dir + "28*")[0]
device_file = device_folder + "/w1_slave"
```
Reading Raw Temperature Data

This function opens the device file and reads its content. It returns the raw temperature data as a list of strings.
```
def read_temp_raw():
    f = open(device_file, "r")
    lines = f.readlines()
    f.close()
    return lines
```

Parsing and Converting Temperature Data

The read_temp function calls read_temp_raw to get the raw data. It waits for a valid temperature reading and then extracts, parses, and converts the temperature to Celsius and Fahrenheit.

def read_temp():
    lines = read_temp_raw()
    while lines[0].strip()[-3:] != "YES":
        time.sleep(0.2)
        lines = read_temp_raw()
    equals_pos = lines[1].find("t=")
    if equals_pos != -1:
        temp_string = lines[1][equals_pos + 2 :]
        temp_c = float(temp_string) / 1000.0
        temp_f = temp_c * 9.0 / 5.0 + 32.0
        return temp_c, temp_f

Main Program Loop and Graceful Exit

The try block contains an infinite loop to continuously read and display the temperature. The except block catches a KeyboardInterrupt to exit the program gracefully.

try:
    while True:
        temp_c, temp_f = read_temp()
        formatted_output = f"Temperature: {temp_c:.2f}°C / {temp_f:.2f}°F"
        print(formatted_output)
        time.sleep(1)
except KeyboardInterrupt:
    print("Exit")