Displaying sensor readings on OLED in Raspberry Pi - Step-by-Step Execution

Concept Flow - Displaying sensor readings on OLED

Start Program

↓

Initialize OLED Display

↓

Initialize Sensor

↓

Read Sensor Data

↓

Format Data for Display

↓

Clear OLED Screen

↓

Display Data on OLED

↓

Wait or Loop

↩Back to Read Sensor Data

The program starts by setting up the OLED and sensor, then repeatedly reads sensor data, formats it, clears the screen, and shows the data on the OLED.

Execution Sample

Raspberry Pi

import board
import adafruit_ssd1306
import time
import random

display = adafruit_ssd1306.SSD1306_I2C(128, 32, board.I2C())
while True:
    temp = random.uniform(20, 30)
    display.fill(0)
    display.text(f"Temp: {temp:.1f} C", 0, 0, 1)
    display.show()
    time.sleep(1)

This code simulates reading a temperature sensor and shows the temperature on the OLED screen every second.

Execution Table

Step	Action	Sensor Reading	Display Buffer Content	Output on OLED
1	Initialize OLED and sensor	N/A	Empty screen buffer	Blank screen
2	Read sensor data	25.3	Empty (before update)	Previous content or blank
3	Clear display buffer	25.3	All pixels off	Screen cleared
4	Write text to buffer	25.3	"Temp: 25.3 C" at (0,0)	Not yet visible
5	Show buffer on OLED	25.3	"Temp: 25.3 C" in buffer	Text displayed on screen
6	Wait 1 second	N/A	Buffer unchanged	Text visible
7	Repeat read sensor	26.1	Buffer with old text	Old text visible
8	Clear display buffer	26.1	All pixels off	Screen cleared
9	Write new text	26.1	"Temp: 26.1 C" at (0,0)	Not yet visible
10	Show buffer on OLED	26.1	"Temp: 26.1 C" in buffer	Updated text displayed
11	Wait 1 second	N/A	Buffer unchanged	Text visible
...	Loop continues	...	...	...

💡 Program runs indefinitely, updating sensor reading and OLED display every second.

Variable Tracker

Variable	Start	After 1	After 2	...final
temp	N/A	25.3	26.1	...
display buffer	Empty	"Temp: 25.3 C"	"Temp: 26.1 C"	...

Key Moments - 3 Insights

Why do we clear the display buffer before writing new text?

Clearing the buffer removes old text so the new sensor reading shows clearly without overlapping. See execution_table rows 3 and 8.

When does the text actually appear on the OLED screen?

Text appears only after calling display.show(), which sends the buffer to the OLED hardware. See execution_table rows 5 and 10.

Why does the program loop reading and displaying sensor data?

Sensors change over time, so looping updates the display with fresh readings continuously. See execution_table rows 2-11.

Visual Quiz - 3 Questions

Look at the execution_table, what is the display buffer content at step 4?

A All pixels off

B "Temp: 25.3 C" at (0,0)

C Empty screen buffer

D Old text from previous reading

💡 Hint

Check the 'Display Buffer Content' column at step 4 in the execution_table.

At which step does the OLED screen get cleared before showing new data?

A Step 2

B Step 5

C Step 3

D Step 7

💡 Hint

Look for 'Clear display buffer' action in the execution_table.

If the sensor reading was not updated in the loop, how would the variable 'temp' change in variable_tracker?

A It would stay the same after start

B It would increase each iteration

C It would be empty

D It would reset to zero

💡 Hint

Refer to the 'temp' row in variable_tracker to see how it changes over iterations.

Concept Snapshot

Displaying sensor readings on OLED:
- Initialize OLED and sensor
- Read sensor data repeatedly
- Clear OLED buffer before writing
- Write formatted text to buffer
- Call display.show() to update screen
- Loop to refresh readings continuously

Full Transcript

This program shows how to display sensor readings on an OLED screen using a Raspberry Pi. First, it sets up the OLED display and sensor. Then it reads the sensor data, clears the OLED screen buffer, writes the new sensor value as text, and updates the OLED display. This process repeats every second to keep the display current. Clearing the buffer before writing prevents overlapping text. The display.show() command sends the buffer content to the screen, making the text visible. The loop ensures the sensor readings and display update continuously.

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