Primal Display: Build a Raspberry Pi LCD Temperature Monitor

This guide shows how to connect a 16x2 HD44780‑compatible LCD to a Raspberry Pi 3 and display live temperature and humidity readings from a DHT11 sensor. The instructions cover hardware selection, wiring (both 4‑bit and 8‑bit modes), required libraries, and a complete Python script.

Story

Introduction

An LCD display is a versatile add‑on for any Raspberry Pi project. By wiring an HD44780‑compatible screen directly to the GPIO pins, you can present sensor data or custom messages without needing I2C or SPI adapters.

Hardware

HD44780‑compatible 16x2 LCD (cost <$10)
Raspberry Pi 3 (or newer)
DHT11 temperature/humidity sensor
Micro‑SD card with Raspbian OS
1–2 10 kΩ potentiometers (contrast/brightness)
Breadboard, jumper wires, and a 5 V power supply

We’ll use six GPIO pins for the LCD; this direct method keeps the Pi’s serial port free and eliminates the need for I2C drivers.

Wiring Things Up

Two wiring options are available:

4‑bit mode – uses 4 data lines, one potentiometer for contrast.
8‑bit mode – uses 8 data lines, two potentiometers (contrast and brightness).

In 4‑bit mode the 8‑bit command byte is split into two 4‑bit halves, so the data bus is half the width. In practice, the LCD’s internal processing time masks any speed advantage of 8‑bit mode, so choose based on available pins.

LCD Pin Connections (4‑bit)

Pin 1 (GND) – Ground
Pin 2 (+5 V) – Power
Pin 3 (Vo) – Potentiometer wiper (contrast)
Pin 4 (RS) – GPIO 37
Pin 5 (RW) – Ground (write‑only)
Pin 6 (EN) – GPIO 35
Pin 7–10 – unused
Pin 11 (D4) – GPIO 33
Pin 12 (D5) – GPIO 31
Pin 13 (D6) – GPIO 29
Pin 14 (D7) – GPIO 23
Pin 15 (LED+) – +5 V
Pin 16 (LED−) – Ground

LCD Pin Connections (8‑bit)

Pin 1 – Ground
Pin 2 – +5 V
Pin 3 – Potentiometer wiper (contrast)
Pin 4 – GPIO 37 (RS)
Pin 5 – Ground (RW)
Pin 6 – GPIO 35 (EN)
Pin 7 (D0) – GPIO 40
Pin 8 (D1) – GPIO 38
Pin 9 (D2) – GPIO 36
Pin 10 (D3) – GPIO 32
Pin 11 (D4) – GPIO 33
Pin 12 (D5) – GPIO 31
Pin 13 (D6) – GPIO 29
Pin 14 (D7) – GPIO 23
Pin 15 – +5 V
Pin 16 – Ground

DHT11 Sensor Wiring

The DHT11 uses three pins: VCC, Data, GND. Connect VCC to 3.3 V (pin 1); if readings are unstable, switch to 5 V (pin 2). Wire the Data pin to GPIO 18 (physical pin 12). A pull‑up resistor (4.7 kΩ) is recommended between VCC and Data.

Required Libraries

Ensure the system has the build tools and Python headers:

sudo apt-get update
sudo apt-get install build-essential python-dev

Install RPLCD for LCD control:

sudo apt-get install python-pip
sudo pip install RPLCD

Install the Adafruit DHT11 library from GitHub:

sudo apt-get install git
git clone https://github.com/adafruit/Adafruit_Python_DHT.git
cd Adafruit_Python_DHT
sudo python setup.py install

Python Script (8‑bit)

Create temperature.py using your preferred editor (e.g., nano):

#!/usr/bin/env python3
import RPi.GPIO as GPIO
import time
import Adafruit_DHT
from RPLCD import CharLCD

GPIO.cleanup()

# LCD configuration – 8‑bit mode
lcd = CharLCD(
    numbering_mode=GPIO.BOARD,
    cols=16,
    rows=2,
    pin_rs=37,
    pin_e=35,
    pins_data=[40, 38, 36, 32, 33, 31, 29, 23]
)

while True:
    humidity, temperature = Adafruit_DHT.read_retry(11, 18)
    if humidity is None or temperature is None:
        print('Failed to retrieve data from sensor')
        continue
    print(f'Temp: {temperature:.1f} C  Humidity: {humidity:.1f} %')
    lcd.clear()
    lcd.cursor_pos = (0, 0)
    lcd.write_string(f'Temp: {int(temperature)} C')
    lcd.cursor_pos = (1, 0)
    lcd.write_string(f'Humidity: {int(humidity)} %')
    time.sleep(5)

Make the script executable and run:

chmod +x temperature.py
./temperature.py

4‑bit Mode Alternative

Replace the pins_data list with four GPIO pins (e.g., [33, 31, 29, 23]) and adjust the LCD initialization accordingly.

Summary

By following these steps, you’ll have a fully functional LCD display that shows real‑time temperature and humidity, perfect for weather stations, IoT dashboards, or educational projects.