Displaying sensor readings on OLED in Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output on the OLED for this code?

This code reads a temperature sensor and displays the value on an OLED screen. What will the OLED show?

Raspberry Pi

import board
import adafruit_ssd1306
import digitalio
import time

i2c = board.I2C()
oled = adafruit_ssd1306.SSD1306_I2C(128, 32, i2c)

sensor_value = 25.3

oled.fill(0)
oled.text(f"Temp: {sensor_value} C", 0, 0, 1)
oled.show()

A The OLED displays: Temp: 25.30 C

B The OLED displays: Temp: 25 C

C The OLED displays: Temp: 25.3 C

D The OLED displays nothing (blank screen)

💡 Hint

Look at how the sensor_value is formatted inside the text function.

The f-string inserts the float value 25.3 directly, so the OLED shows exactly 'Temp: 25.3 C'. No rounding or extra decimals are added.

🧠 Conceptual

intermediate

Why do we call oled.show() after oled.text()?

In code that writes text to an OLED screen, why is it necessary to call oled.show() after oled.text()?

A oled.text() writes text to a buffer; oled.show() updates the screen with the buffer content.

B oled.show() clears the screen before oled.text() writes text.

C oled.text() directly updates the screen; oled.show() is optional and does nothing.

D oled.show() turns the OLED on; oled.text() only works if the screen is on.

💡 Hint

Think about how drawing on a screen usually works with buffers.

The oled.text() function writes text to an internal memory buffer. The oled.show() function sends this buffer to the OLED hardware to update the visible display.

🔧 Debug

advanced

Why does this OLED code raise an error?

This code tries to display humidity on the OLED but raises an error. What is the cause?

Raspberry Pi

import board
import adafruit_ssd1306

i2c = board.I2C()
oled = adafruit_ssd1306.SSD1306_I2C(128, 32, i2c)

humidity = 55

oled.fill(0)
oled.text(f"Humidity: {humidity}%", 0, 0, 1)
oled.show()

A No error; code runs and displays 'Humidity: 55%'

B TypeError because humidity is an int, not a string

C RuntimeError because oled.text() does not accept % character

D SyntaxError due to % symbol inside f-string without escaping

💡 Hint

Check how % is used inside f-strings in Python.

The % character inside an f-string is treated as a normal character unless used in formatting expressions. Here it is safe and does not cause errors.

📝 Syntax

advanced

Which option fixes the syntax error in this OLED display code?

This code has a syntax error. Which option fixes it?

Raspberry Pi

import board
import adafruit_ssd1306

i2c = board.I2C()
oled = adafruit_ssd1306.SSD1306_I2C(128, 32, i2c)

sensor = 30

oled.fill(0)
oled.text(f"Value: {sensor", 0, 0, 1)
oled.show()

A oled.text(f"Value: sensor", 0, 0, 1)

B oled.text(f"Value: {sensor}" 0, 0, 1)

C oled.text(f"Value: {sensor})", 0, 0, 1)

D oled.text(f"Value: {sensor}", 0, 0, 1)

💡 Hint

Check the placement of braces and commas inside the f-string.

Option D correctly closes the curly brace and the string, and separates arguments with commas. Others have missing braces, quotes, or commas causing syntax errors.

🚀 Application

expert

How many lines of text can fit on a 128x32 OLED if each line is 8 pixels tall?

You want to display multiple sensor readings on a 128x32 OLED screen. Each text line uses 8 pixels in height. How many lines can you display without overlap?

A 32 lines

B 4 lines

C 8 lines

D 16 lines

💡 Hint

Divide the total height by the height of one line.

The screen height is 32 pixels. Each line is 8 pixels tall. 32 / 8 = 4 lines fit exactly.

Practice

1. What is the main purpose of using an OLED screen with a Raspberry Pi when working with sensors?

easy

A. To increase the sensor's accuracy

B. To store sensor data permanently

C. To display sensor readings clearly and in real-time

D. To power the sensors automatically

Solution

1. Step 1: Understand OLED screen function

   OLED screens are used to show information visually, such as text or images.

2. Step 2: Relate to sensor data usage

   Displaying sensor readings on OLED helps users see live data clearly and quickly.

3. Final Answer:

   To display sensor readings clearly and in real-time -> Option C

4. Quick Check:

   OLED shows sensor data live = A [OK]

Hint: OLED screens show live sensor data visually [OK]

Common Mistakes:

• Thinking OLED stores data permanently
• Confusing display with sensor accuracy
• Assuming OLED powers sensors

2. Which Python library is commonly used to control an SSD1306 OLED display on a Raspberry Pi?

easy

A. Adafruit_SSD1306

B. matplotlib

C. pygame

D. numpy

Solution

1. Step 1: Identify libraries for OLED control

   Adafruit_SSD1306 is a popular Python library designed to control SSD1306 OLED displays.

2. Step 2: Exclude unrelated libraries

   matplotlib and pygame are for graphics but not specific to OLED control; numpy is for math operations.

3. Final Answer:

   Adafruit_SSD1306 -> Option A

4. Quick Check:

   Use Adafruit_SSD1306 for SSD1306 OLED [OK]

Hint: Use Adafruit_SSD1306 library for SSD1306 OLED screens [OK]

Common Mistakes:

• Choosing matplotlib which is for plotting graphs
• Selecting pygame meant for game development
• Picking numpy which is for numerical calculations

3. What will be the output on the OLED if the following Python code runs successfully?

import Adafruit_SSD1306
from PIL import Image, ImageDraw, ImageFont

# Initialize display
disp = Adafruit_SSD1306.SSD1306_128_64(rst=None)
disp.begin()
disp.clear()
disp.display()

# Create blank image for drawing
width = disp.width
height = disp.height
image = Image.new('1', (width, height))
draw = ImageDraw.Draw(image)

# Draw text
font = ImageFont.load_default()
draw.text((0, 0), 'Temp: 25C', font=font, fill=255)

# Display image
disp.image(image)
disp.display()

medium

A. The OLED will show a white screen with no text

B. The OLED will remain blank

C. The code will cause a syntax error

D. The OLED will show the text 'Temp: 25C' at the top-left corner

Solution

1. Step 1: Analyze text drawing commands

   The code draws 'Temp: 25C' at position (0,0) using a default font on a blank image.

2. Step 2: Understand display update

   Calling disp.image(image) and disp.display() sends the image to the OLED, showing the text.

3. Final Answer:

   The OLED will show the text 'Temp: 25C' at the top-left corner -> Option D

4. Quick Check:

   Text drawn and displayed = A [OK]

Hint: Text drawn at (0,0) appears top-left on OLED [OK]

Common Mistakes:

• Assuming display stays blank without disp.display()
• Confusing image creation with display output
• Thinking code has syntax errors

4. Identify the error in this code snippet meant to update an OLED with sensor data:

disp = Adafruit_SSD1306.SSD1306_128_64(rst=None)
disp.begin()
disp.clear()

image = Image.new('1', (disp.width, disp.height))
draw = ImageDraw.Draw(image)
font = ImageFont.load_default()

sensor_value = 30

draw.text((0, 0), f'Temp: {sensor_value}C', font=font, fill=255)

# Missing disp.image(image) here

disp.display()

medium

A. Missing disp.image(image) before disp.display()

B. Incorrect font loading method

C. Image size does not match display size

D. disp.clear() should be called after disp.display()

Solution

1. Step 1: Check display update sequence

   To update OLED, image must be sent with disp.image(image) before disp.display().

2. Step 2: Identify missing command

   The code misses disp.image(image), so display shows old or blank content.

3. Final Answer:

   Missing disp.image(image) before disp.display() -> Option A

4. Quick Check:

   disp.image(image) needed before disp.display() [OK]

Hint: Always call disp.image(image) before disp.display() [OK]

Common Mistakes:

• Forgetting to send image to display
• Calling disp.clear() too late
• Using wrong font loading method

5. You want to continuously display live temperature readings from a sensor on an OLED screen using Python. Which approach correctly updates the display every second without flickering?

import time
while True:
    temp = read_sensor()
    image = Image.new('1', (disp.width, disp.height))
    draw = ImageDraw.Draw(image)
    draw.text((0, 0), f'Temp: {temp}C', font=font, fill=255)
    disp.image(image)
    disp.display()
    time.sleep(1)

What is the best improvement to reduce flicker?

hard

A. Clear the display before drawing each new image

B. Create the image and draw objects once outside the loop and reuse them

C. Remove time.sleep(1) to update faster

D. Use disp.clear() after disp.display() inside the loop

Solution

1. Step 1: Understand flicker cause

   Creating new image and draw objects each loop causes flicker due to redraw overhead.

2. Step 2: Optimize by reusing objects

   Creating image and draw once outside loop and clearing draw area inside loop reduces flicker.

3. Final Answer:

   Create the image and draw objects once outside the loop and reuse them -> Option B

4. Quick Check:

   Reuse image/draw objects to reduce flicker [OK]

Hint: Create image/draw once outside loop to avoid flicker [OK]

Common Mistakes:

• Recreating image each loop causing flicker
• Removing sleep causing too fast updates
• Calling disp.clear() after display has no effect