LCD display (16x2) with I2C backpack in Raspberry Pi

Introduction

An LCD display with I2C backpack lets you show text on a small screen using just two wires. It makes your Raspberry Pi projects easy to read and interact with.

You want to display sensor readings like temperature or humidity.

You need a simple status message for your Raspberry Pi project.

You want to show a menu or options without a full monitor.

You want to save GPIO pins by using I2C instead of many wires.

Syntax

Raspberry Pi

from RPLCD.i2c import CharLCD

lcd = CharLCD('PCF8574', 0x27)
lcd.write_string('Hello World!')

Use the RPLCD library to control the LCD easily.

The address 0x27 is common but may differ; check your device.

Examples

Shows 'Hi!' on the LCD screen.

Raspberry Pi

from RPLCD.i2c import CharLCD

lcd = CharLCD('PCF8574', 0x27)
lcd.write_string('Hi!')

Writes 'Line 2 text' on the second line of the LCD at the first position.

Raspberry Pi

from RPLCD.i2c import CharLCD

lcd = CharLCD('PCF8574', 0x3F)
lcd.cursor_pos = (1, 0)
lcd.write_string('Line 2 text')

Clears the screen before writing new text.

Raspberry Pi

from RPLCD.i2c import CharLCD

lcd = CharLCD('PCF8574', 0x27)
lcd.clear()
lcd.write_string('Cleared and new')

Sample Program

This program shows a greeting on the first line and a description on the second line of the LCD. It waits 5 seconds so you can read it, then clears the screen.

Raspberry Pi

from RPLCD.i2c import CharLCD
import time

# Create LCD object with I2C address 0x27
lcd = CharLCD('PCF8574', 0x27)

# Clear the display
lcd.clear()

# Write first line
lcd.cursor_pos = (0, 0)
lcd.write_string('Hello, Pi!')

# Write second line
lcd.cursor_pos = (1, 0)
lcd.write_string('I2C LCD Demo')

# Keep message for 5 seconds
time.sleep(5)

# Clear before exit
lcd.clear()

Important Notes

Make sure your Raspberry Pi has I2C enabled in settings.

Check your LCD's I2C address with sudo i2cdetect -y 1 if unsure.

Use lcd.clear() to erase the screen before writing new text.

Summary

LCD with I2C backpack uses fewer wires and is easy to control from Raspberry Pi.

Use the RPLCD Python library to write text and control cursor position.

Always clear the screen before writing new messages for clarity.

Practice

1. What is the main advantage of using an I2C backpack with a 16x2 LCD on a Raspberry Pi?

easy

A. It powers the Raspberry Pi without an external source

B. It reduces the number of GPIO pins needed to control the LCD

C. It allows the LCD to display colors

D. It increases the LCD resolution beyond 16x2

Solution

1. Step 1: Understand I2C backpack purpose

   The I2C backpack simplifies wiring by using only two data lines (SDA and SCL) instead of many GPIO pins.

2. Step 2: Compare options

   Options A, B, and C are unrelated to I2C backpacks; only It reduces the number of GPIO pins needed to control the LCD correctly states the advantage.

3. Final Answer:

   It reduces the number of GPIO pins needed to control the LCD -> Option B

4. Quick Check:

   I2C reduces wiring = D [OK]

Hint: I2C means fewer wires needed for LCD control [OK]

Common Mistakes:

• Thinking I2C changes LCD resolution
• Assuming I2C adds color support
• Confusing power supply with data interface

2. Which Python library is commonly used to control a 16x2 LCD with an I2C backpack on Raspberry Pi?

easy

A. NumPy

B. PIL

C. RPLCD

D. Matplotlib

Solution

1. Step 1: Identify libraries purpose

   RPLCD is designed for controlling LCD displays, including those with I2C backpacks.

2. Step 2: Eliminate unrelated libraries

   PIL is for images, NumPy for math arrays, Matplotlib for plotting; none control LCDs.

3. Final Answer:

   RPLCD -> Option C

4. Quick Check:

   LCD control library = RPLCD [OK]

Hint: RPLCD is the go-to library for LCDs on Raspberry Pi [OK]

Common Mistakes:

• Confusing image or math libraries with LCD control
• Using libraries without I2C support
• Misspelling library names

3. What will be the output on the LCD after running this Python code snippet?

from RPLCD.i2c import CharLCD
lcd = CharLCD('PCF8574', 0x27)
lcd.write_string('Hello\nWorld!')

medium

A. Hello on first line, World! on second line

B. HelloWorld! on first line only

C. SyntaxError due to newline character

D. Nothing displayed because address is wrong

Solution

1. Step 1: Understand write_string with newline

   The '\n' moves the cursor to the second line on the LCD.

2. Step 2: Check address and syntax

   Address 0x27 is a common default; no syntax error in code.

3. Final Answer:

   Hello on first line, World! on second line -> Option A

4. Quick Check:

   Newline moves text to line 2 = C [OK]

Hint: Use '\n' to move to second line on LCD [OK]

Common Mistakes:

• Thinking '\n' causes syntax error
• Assuming text stays on one line
• Using wrong I2C address without checking

4. Identify the error in this code snippet for initializing the LCD with I2C backpack:

from RPLCD.i2c import CharLCD
lcd = CharLCD(i2c_expander='PCF8574', address=0x3F)
lcd.write_string('Test')

medium

A. Missing 'port' parameter for CharLCD initialization

B. The parameter name should be 'address' not 'i2c_expander'

C. The I2C address 0x3F is invalid for this device

D. The parameter 'i2c_expander' should be 'i2c_expander' but is correct here

Solution

1. Step 1: Check CharLCD parameters

   CharLCD requires 'i2c_expander', 'address', and 'port' parameters for I2C setup.

2. Step 2: Identify missing parameter

   The code misses the 'port' parameter, which is needed to specify the I2C bus number.

3. Final Answer:

   Missing 'port' parameter for CharLCD initialization -> Option A

4. Quick Check:

   Missing required 'port' parameter = A [OK]

Hint: Always include 'port' when initializing CharLCD with I2C [OK]

Common Mistakes:

• Assuming address 0x3F is always wrong
• Confusing parameter names
• Omitting required parameters

5. You want to display a scrolling message on a 16x2 LCD with I2C backpack using Python. Which approach is best?

hard

A. Write the full message once and rely on LCD auto-scroll

B. Change the I2C address dynamically during scrolling

C. Clear the LCD and write the full message repeatedly without delay

D. Use a loop to write substrings shifting one character at a time with delays

Solution

1. Step 1: Understand scrolling on 16x2 LCD

   The LCD does not auto-scroll long messages; you must manually shift text.

2. Step 2: Choose method to scroll

   Using a loop to write substrings with delays simulates scrolling smoothly.

3. Step 3: Eliminate wrong options

   Write the full message once and rely on LCD auto-scroll is incorrect because LCD won't auto-scroll; C causes flicker; D is unrelated.

4. Final Answer:

   Use a loop to write substrings shifting one character at a time with delays -> Option D

5. Quick Check:

   Manual substring loop scrolls text = B [OK]

Hint: Scroll by shifting substrings in a timed loop [OK]

Common Mistakes:

• Expecting LCD to auto-scroll long text
• Clearing display too often causing flicker
• Trying to change I2C address during scrolling