LCD display (16x2) with I2C backpack in Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output on the LCD after running this code?

Consider this Python code snippet for a Raspberry Pi connected to a 16x2 LCD with an I2C backpack. What text will appear on the first line of the LCD?

Raspberry Pi

import I2C_LCD_driver
lcd = I2C_LCD_driver.LCD()
lcd.lcd_display_string("Hello, World!", 1)
lcd.lcd_display_string("Line 2 Text", 2)

A Hello, World! on line 1 and Line 2 Text on line 2

B Line 2 Text on line 1 and Hello, World! on line 2

C Only Hello, World! on line 1, line 2 is blank

D Only Line 2 Text on line 2, line 1 is blank

💡 Hint

Look at the lcd_display_string method parameters: the string and the line number.

The lcd_display_string method takes the text and the line number (1 or 2). The first call writes "Hello, World!" on line 1, the second call writes "Line 2 Text" on line 2.

🧠 Conceptual

intermediate

Which I2C address is most commonly used for a 16x2 LCD with I2C backpack?

You want to communicate with a 16x2 LCD using I2C on Raspberry Pi. Which I2C address is typically used by these backpacks?

A 0x50

B 0x3F

C 0x68

D 0x27

💡 Hint

Common I2C backpack modules usually use either 0x27 or 0x3F.

Most 16x2 LCD I2C backpacks use the address 0x27 by default. Some use 0x3F, but 0x27 is more common.

🔧 Debug

advanced

Why does this code raise an error when initializing the LCD?

Look at this code snippet. It raises an AttributeError: module 'I2C_LCD_driver' has no attribute 'lcd'. What is the cause?

Raspberry Pi

import I2C_LCD_driver
lcd = I2C_LCD_driver.lcd()
lcd.lcd_display_string("Test", 1)

A The module I2C_LCD_driver is not installed

B The lcd_display_string method does not exist

C The class name is capitalized as 'LCD' not 'lcd' in the module

D The I2C address is incorrect

💡 Hint

Check the exact class name in the I2C_LCD_driver module.

The class in I2C_LCD_driver is named 'LCD' with uppercase letters, not 'lcd'. Python is case-sensitive, so calling 'lcd()' causes AttributeError.

📝 Syntax

advanced

Which option correctly initializes the LCD and clears the display?

You want to initialize the LCD and clear any previous text. Which code snippet is correct?

A

lcd = I2C_LCD_driver.LCD()
lcd.clear()

B

lcd = I2C_LCD_driver.LCD()
lcd.lcd_clear()

C

lcd = I2C_LCD_driver.lcd()
lcd.lcd_clear()

D

lcd = I2C_LCD_driver.LCD()
lcd.clear_display()

💡 Hint

Check the method name for clearing the display in the library.

The method to clear the LCD in I2C_LCD_driver is 'lcd_clear()'. The class name is 'LCD'.

🚀 Application

expert

How many characters can you display on a 16x2 LCD at once?

You have a 16x2 LCD connected via I2C. How many characters can you show on the screen at the same time?

A 32 characters

B 64 characters

C 2 characters

D 16 characters

💡 Hint

Think about the number of columns and rows multiplied.

A 16x2 LCD has 16 columns and 2 rows, so it can display 16 * 2 = 32 characters simultaneously.

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