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GPIO Project 9 - LCD Temperature

Beginner
30 Minuten
€167.09

In this project, you will learn how to use aDS18B20 temperature sensor to measure the ambient temperature and display this value on a16x2 LCD display with I2C interface. This is a great application to present data visually.

Connection diagram

Connection of the DS18B20 temperature sensor:

  1. Zwart draad: Connect with GND (pin 6).
  2. Rood wire: Connection with 3.3V (pin 1).
  3. Geel draad:
    • Connect with GPIO 4 (pin 7).
    • Plaats a 10kΩ weerstand tussen de gele draad en 3.3V ( pin 1).

Connect het LCD display:

  1. VCC: Connection with 5V (pin 2).
  2. GND: Connect with GND (pin 6).
  3. SDA: Connect with GPIO 2 (pin 3).
  4. SCL: Connection with GPIO 3 (pin 5).

Pinout Reference

GPIO

Pin #

Function

Connection

GPIO 4Pin 7Temperature sensor dataDS18B20-yellow wire
GPIO 2Pin 3I2C SDALCD SDA
GPIO 3Pin 5I2C SCLLCD SCL
3.3VPin 1NutritionDS18B20-red wire
5VPin 2NutritionLCD VCC
GNDPin 6Earth (Ground)DS18B20 and LCD

 

Preparation

Step 1: Install required libraries

Run the following commands in the terminal to install the libraries for the DS18B20 and LCD:

sudo apt-get update
sudo apt-get install python3-pip
pip3 install RPLCD

Activate the 1-Wire interface for the DS18B20:

  1. Open the configuration menu:
sudo raspi-config
  1. Go to Interface Options > 1-Wire and turn it on.
  2. Reboot the Raspberry Pi.

Check if the DS18B20 is recognized:

ls /sys/bus/w1/devices/

You would see an address like 28-XXXXXXXXXXXX.

Python-code in Thonny

Step 1: Write your code

Open the Thonny Python IDE and enter the following code:

import os
import glob
from time import sleep
from RPLCD.i2c import CharLCD

# DS18B20-instellingen
base_dir = '/sys/bus/w1/devices/'
device_folder = glob.glob(base_dir + '28*')[0]
device_file = device_folder + '/w1_slave'

# LCD-instellingen
lcd = CharLCD(i2c_expander='PCF8574', address=0x27, cols=16, rows=2)

def read_temp_raw():
    """Lees ruwe data van de DS18B20."""
    with open(device_file, 'r') as f:
        lines = f.readlines()
    return lines

def read_temp():
    """Verwerk de data en retourneer de temperatuur in graden Celsius."""
    lines = read_temp_raw()
    while lines[0].strip()[-3:] != 'YES':
        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
        return temp_c

try:
    while True:
        temp = read_temp()
        print(f"Temperatuur: {temp:.1f} °C")
        
        # Toon de temperatuur op het LCD
        lcd.clear()
        lcd.write_string("Temp: {:.1f} C".format(temp))
        
        sleep(2)

except KeyboardInterrupt:
    print("\nProgramma gestopt.")
    lcd.clear()

Step 2: Save the file

Click File > Save As and name the file lcd_temperature.py.

Step 3: Run the script

Click the greenRun button (▶) at the top the Thonny interface.

How does it work?

  1. DS18B20 Temperature Sensor:
    • Reads the temperature via 1-Wire protocol and returns the value in degrees Celsius.
  2. LCD Display:
    • Displays the temperature value on a 16x2 LCD display.
  3. Repeat:
    • The program reads and displays the temperature every 2 seconds.

Result

  • The ambient temperature is continuously read by the DS18B20 and displayed on the LCD screen.
  • The temperature is also displayed in the terminal.

Experimenting

  1. Add Fahrenheit:
    • Add code to display Fahrenheit as well:
      python
      Copy code
  2. Add LED:
    • Turn on an LED when the temperature exceeds a threshold.
  3. Logging:
    • Log the temperature to a file for further analysis:
with open("temp_log.txt", "a") as log:
    log.write(f"{temp:.1f} °C\n")

Required products