OLED display with I2C (SSD1306) in Arduino - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output on the OLED display?

Consider this Arduino code snippet using the SSD1306 OLED display with I2C. What text will appear on the screen?

Arduino

#include <Wire.h>
#include <Adafruit_SSD1306.h>

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define OLED_RESET -1
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);

void setup() {
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
  display.clearDisplay();
  display.setTextSize(2);
  display.setTextColor(SSD1306_WHITE);
  display.setCursor(10, 10);
  display.println("Hi!");
  display.display();
}

void loop() {}

A The OLED shows the text 'Hi!' near the top-left corner.

B The OLED shows the text 'Hi!' centered on the screen.

C The OLED remains blank because display.display() is missing.

D The OLED shows random pixels because display.clearDisplay() is called after display.display().

💡 Hint

Look at where the cursor is set and what text is printed before calling display.display().

The code sets the cursor at (10,10) and prints 'Hi!' with text size 2. Then display.display() updates the screen. So the text appears near the top-left corner.

❓ Predict Output

intermediate

What happens if you call display.clearDisplay() after display.display()?

In this Arduino code, what will be the visible result on the OLED screen?

Arduino

#include <Wire.h>
#include <Adafruit_SSD1306.h>

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define OLED_RESET -1
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);

void setup() {
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
  display.setTextSize(1);
  display.setTextColor(SSD1306_WHITE);
  display.setCursor(0, 0);
  display.println("Hello");
  display.display();
  display.clearDisplay();
}

void loop() {}

A The OLED screen remains blank.

B The OLED shows 'Hello' text on the screen.

C The OLED shows 'Hello' but flickers continuously.

D The OLED shows random pixels because clearDisplay() corrupts the buffer.

💡 Hint

Remember that display.display() sends the buffer to the screen, but clearDisplay() clears the buffer after that.

display.display() pushes the buffer (with 'Hello') to the screen. clearDisplay() then clears the internal buffer, but since there's no further display.display() call and loop() is empty, the screen retains the 'Hello' text.

🔧 Debug

advanced

Why does this code fail to display text on the OLED?

Look at this Arduino code snippet. It compiles but the OLED screen stays blank. What is the main reason?

Arduino

#include <Wire.h>
#include <Adafruit_SSD1306.h>

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define OLED_RESET -1
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);

void setup() {
  display.begin(SSD1306_SWITCHCAPVCC, 0x3D);
  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(SSD1306_WHITE);
  display.setCursor(0,0);
  display.println("Test");
  display.display();
}

void loop() {}

A The display.begin() call is missing the reset pin argument.

B The text size 1 is too small to be visible on the OLED.

C The display.clearDisplay() must be called after display.display().

D The I2C address 0x3D is incorrect for this OLED module; it should be 0x3C.

💡 Hint

Check the I2C address used in display.begin().

Most SSD1306 OLED modules use I2C address 0x3C. Using 0x3D means the display is not found, so nothing shows.

📝 Syntax

advanced

Which option causes a compilation error?

Which of these code snippets will cause a compilation error when using the Adafruit_SSD1306 library?

A display.setTextSize(2); display.setTextColor(SSD1306_WHITE); display.setCursor(0,0); display.println("Hi"); display.display();

B display.setTextSize(2); display.setTextColor(SSD1306_WHITE); display.setCursor(0,0); display.print("Hi"); display.display();

C display.setTextSize(2); display.setTextColor(WHITE); display.setCursor(0,0); display.println("Hi"); display.display();

D display.setTextSize(2); display.setTextColor(SSD1306_WHITE); display.setCursor(0,0); display.println("Hi");

💡 Hint

Check the constant used for text color.

SSD1306_WHITE is the correct constant for white color in this library. Using WHITE alone causes a compilation error because it is undefined.

🚀 Application

expert

How many pixels are lit after this code runs?

This code draws a filled rectangle on the OLED screen. How many pixels will be lit (white) after running?

Arduino

#include <Wire.h>
#include <Adafruit_SSD1306.h>

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define OLED_RESET -1
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);

void setup() {
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
  display.clearDisplay();
  display.fillRect(10, 10, 20, 15, SSD1306_WHITE);
  display.display();
}

void loop() {}

A 300 pixels

B 320 pixels

C 310 pixels

D 290 pixels

💡 Hint

Calculate width × height of the rectangle.

The rectangle is 20 pixels wide and 15 pixels tall. 20 × 15 = 300 pixels lit.