Displaying sensor readings on OLED in Raspberry Pi - Mini Project: Build & Apply

Displaying sensor readings on OLED

📖 Scenario: You have a Raspberry Pi connected to a temperature sensor and a small OLED screen. You want to show the current temperature on the OLED screen so you can easily see it without using a computer screen.

🎯 Goal: Build a simple Python program that reads a temperature value from a sensor variable and displays it on the OLED screen.

📋 What You'll Learn

Create a variable to hold the temperature reading.

Set up a variable for the OLED display width.

Write code to format the temperature reading as a string.

Display the formatted temperature string on the OLED screen.

💡 Why This Matters

🌍 Real World

Displaying sensor readings on small screens is common in home automation, weather stations, and portable devices.

💼 Career

Understanding how to handle sensor data and display it on hardware screens is useful for embedded systems and IoT developer roles.

1

Create the temperature reading variable

Create a variable called temperature_celsius and set it to the value 23.5 to represent the current temperature reading.

Raspberry Pi

# Create a variable called temperature_celsius and set it to 23.5
# Your code here

Hint

Use a simple assignment like temperature_celsius = 23.5.

2

Set up the OLED display width variable

Create a variable called oled_width and set it to 128 to represent the width of the OLED display in pixels.

Raspberry Pi

temperature_celsius = 23.5
# Create a variable called oled_width and set it to 128
# Your code here

Hint

Use oled_width = 128 to set the display width.

3

Format the temperature reading as a string

Create a variable called display_text that stores the temperature reading formatted as a string like "Temp: 23.5°C" using an f-string and the variable temperature_celsius.

Raspberry Pi

temperature_celsius = 23.5
oled_width = 128
# Create a variable called display_text with the value 'Temp: 23.5°C' using an f-string
# Your code here

Hint

Use an f-string like f"Temp: {temperature_celsius}°C" to create the display text.

4

Display the temperature on the OLED screen

Use print(display_text) to simulate displaying the temperature on the OLED screen by printing the formatted temperature string.

Raspberry Pi

temperature_celsius = 23.5
oled_width = 128
display_text = f"Temp: {temperature_celsius}°C"
# Print the display_text to simulate OLED output
# Your code here

Hint

Use print(display_text) to show the temperature.

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