I2C header tested using a SH1106 128x64 OLED for techexplorations.com/blog/course/advanced-pcb-design-kicad

SH1106_128x64_i2c_QTPY.ino

/*********************************************************************
  This is an example for our Monochrome OLEDs based on SH110X drivers

  This example is for a 128x64 size display using I2C to communicate
  3 pins are required to interface (2 I2C and one reset)

  Adafruit invests time and resources providing this open source code,
  please support Adafruit and open-source hardware by purchasing
  products from Adafruit!

  Written by Limor Fried/Ladyada  for Adafruit Industries.
  BSD license, check license.txt for more information
  All text above, and the splash screen must be included in any redistribution

  i2c SH1106 modified by Rupert Hirst  12/09/21
*********************************************************************/



#include <SPI.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SH110X.h>

/* Uncomment the initialize the I2C address , uncomment only one, If you get a totally blank screen try the other*/
#define i2c_Address 0x3c //initialize with the I2C addr 0x3C Typically eBay OLED's
//#define i2c_Address 0x3d //initialize with the I2C addr 0x3D Typically Adafruit OLED's

#define SDA_PIN 4  // SDA pin connected to GPIO 04
#define SCL_PIN 3  // SCL pin connected to GPIO 03

#define SCREEN_WIDTH 128 // OLED display width, in pixels
#define SCREEN_HEIGHT 64 // OLED display height, in pixels
#define OLED_RESET -1   //   QT-PY / XIAO
Adafruit_SH1106G display = Adafruit_SH1106G(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);


#define NUMFLAKES 10
#define XPOS 0
#define YPOS 1
#define DELTAY 2


#define LOGO16_GLCD_HEIGHT 16
#define LOGO16_GLCD_WIDTH  16
static const unsigned char PROGMEM logo16_glcd_bmp[] =
{ B00000000, B11000000,
  B00000001, B11000000,
  B00000001, B11000000,
  B00000011, B11100000,
  B11110011, B11100000,
  B11111110, B11111000,
  B01111110, B11111111,
  B00110011, B10011111,
  B00011111, B11111100,
  B00001101, B01110000,
  B00011011, B10100000,
  B00111111, B11100000,
  B00111111, B11110000,
  B01111100, B11110000,
  B01110000, B01110000,
  B00000000, B00110000
};


void setup()   {

  Serial.begin(9600);

   // Initialize I2C with custom SDA and SCL pins
  Wire.begin(SDA_PIN, SCL_PIN);

  // Show image buffer on the display hardware.
  // Since the buffer is intialized with an Adafruit splashscreen
  // internally, this will display the splashscreen.

  delay(250); // wait for the OLED to power up
  display.begin(i2c_Address, true); // Address 0x3C default
 //display.setContrast (0); // dim display
 
  display.display();
  delay(2000);

  // Clear the buffer.
  display.clearDisplay();

  // draw a single pixel
  display.drawPixel(10, 10, SH110X_WHITE);
  // Show the display buffer on the hardware.
  // NOTE: You _must_ call display after making any drawing commands
  // to make them visible on the display hardware!
  display.display();
  delay(2000);
  display.clearDisplay();

  // draw many lines
  testdrawline();
  display.display();
  delay(2000);
  display.clearDisplay();

  // draw rectangles
  testdrawrect();
  display.display();
  delay(2000);
  display.clearDisplay();

  // draw multiple rectangles
  testfillrect();
  display.display();
  delay(2000);
  display.clearDisplay();

  // draw mulitple circles
  testdrawcircle();
  display.display();
  delay(2000);
  display.clearDisplay();

  // draw a SH110X_WHITE circle, 10 pixel radius
  display.fillCircle(display.width() / 2, display.height() / 2, 10, SH110X_WHITE);
  display.display();
  delay(2000);
  display.clearDisplay();

  testdrawroundrect();
  delay(2000);
  display.clearDisplay();

  testfillroundrect();
  delay(2000);
  display.clearDisplay();

  testdrawtriangle();
  delay(2000);
  display.clearDisplay();

  testfilltriangle();
  delay(2000);
  display.clearDisplay();

  // draw the first ~12 characters in the font
  testdrawchar();
  display.display();
  delay(2000);
  display.clearDisplay();



  // text display tests
  display.setTextSize(1);
  display.setTextColor(SH110X_WHITE);
  display.setCursor(0, 0);
  display.println("Failure is always an option");
  display.setTextColor(SH110X_BLACK, SH110X_WHITE); // 'inverted' text
  display.println(3.141592);
  display.setTextSize(2);
  display.setTextColor(SH110X_WHITE);
  display.print("0x"); display.println(0xDEADBEEF, HEX);
  display.display();
  delay(2000);
  display.clearDisplay();

  // miniature bitmap display
  display.drawBitmap(30, 16,  logo16_glcd_bmp, 16, 16, 1);
  display.display();
  delay(1);

  // invert the display
  display.invertDisplay(true);
  delay(1000);
  display.invertDisplay(false);
  delay(1000);
  display.clearDisplay();

  // draw a bitmap icon and 'animate' movement
  testdrawbitmap(logo16_glcd_bmp, LOGO16_GLCD_HEIGHT, LOGO16_GLCD_WIDTH);
}


void loop() {

}


void testdrawbitmap(const uint8_t *bitmap, uint8_t w, uint8_t h) {
  uint8_t icons[NUMFLAKES][3];

  // initialize
  for (uint8_t f = 0; f < NUMFLAKES; f++) {
    icons[f][XPOS] = random(display.width());
    icons[f][YPOS] = 0;
    icons[f][DELTAY] = random(5) + 1;

    Serial.print("x: ");
    Serial.print(icons[f][XPOS], DEC);
    Serial.print(" y: ");
    Serial.print(icons[f][YPOS], DEC);
    Serial.print(" dy: ");
    Serial.println(icons[f][DELTAY], DEC);
  }

  while (1) {
    // draw each icon
    for (uint8_t f = 0; f < NUMFLAKES; f++) {
      display.drawBitmap(icons[f][XPOS], icons[f][YPOS], bitmap, w, h, SH110X_WHITE);
    }
    display.display();
    delay(200);

    // then erase it + move it
    for (uint8_t f = 0; f < NUMFLAKES; f++) {
      display.drawBitmap(icons[f][XPOS], icons[f][YPOS], bitmap, w, h, SH110X_BLACK);
      // move it
      icons[f][YPOS] += icons[f][DELTAY];
      // if its gone, reinit
      if (icons[f][YPOS] > display.height()) {
        icons[f][XPOS] = random(display.width());
        icons[f][YPOS] = 0;
        icons[f][DELTAY] = random(5) + 1;
      }
    }
  }
}


void testdrawchar(void) {
  display.setTextSize(1);
  display.setTextColor(SH110X_WHITE);
  display.setCursor(0, 0);

  for (uint8_t i = 0; i < 168; i++) {
    if (i == '\n') continue;
    display.write(i);
    if ((i > 0) && (i % 21 == 0))
      display.println();
  }
  display.display();
  delay(1);
}

void testdrawcircle(void) {
  for (int16_t i = 0; i < display.height(); i += 2) {
    display.drawCircle(display.width() / 2, display.height() / 2, i, SH110X_WHITE);
    display.display();
    delay(1);
  }
}

void testfillrect(void) {
  uint8_t color = 1;
  for (int16_t i = 0; i < display.height() / 2; i += 3) {
    // alternate colors
    display.fillRect(i, i, display.width() - i * 2, display.height() - i * 2, color % 2);
    display.display();
    delay(1);
    color++;
  }
}

void testdrawtriangle(void) {
  for (int16_t i = 0; i < min(display.width(), display.height()) / 2; i += 5) {
    display.drawTriangle(display.width() / 2, display.height() / 2 - i,
                         display.width() / 2 - i, display.height() / 2 + i,
                         display.width() / 2 + i, display.height() / 2 + i, SH110X_WHITE);
    display.display();
    delay(1);
  }
}

void testfilltriangle(void) {
  uint8_t color = SH110X_WHITE;
  for (int16_t i = min(display.width(), display.height()) / 2; i > 0; i -= 5) {
    display.fillTriangle(display.width() / 2, display.height() / 2 - i,
                         display.width() / 2 - i, display.height() / 2 + i,
                         display.width() / 2 + i, display.height() / 2 + i, SH110X_WHITE);
    if (color == SH110X_WHITE) color = SH110X_BLACK;
    else color = SH110X_WHITE;
    display.display();
    delay(1);
  }
}

void testdrawroundrect(void) {
  for (int16_t i = 0; i < display.height() / 2 - 2; i += 2) {
    display.drawRoundRect(i, i, display.width() - 2 * i, display.height() - 2 * i, display.height() / 4, SH110X_WHITE);
    display.display();
    delay(1);
  }
}

void testfillroundrect(void) {
  uint8_t color = SH110X_WHITE;
  for (int16_t i = 0; i < display.height() / 2 - 2; i += 2) {
    display.fillRoundRect(i, i, display.width() - 2 * i, display.height() - 2 * i, display.height() / 4, color);
    if (color == SH110X_WHITE) color = SH110X_BLACK;
    else color = SH110X_WHITE;
    display.display();
    delay(1);
  }
}

void testdrawrect(void) {
  for (int16_t i = 0; i < display.height() / 2; i += 2) {
    display.drawRect(i, i, display.width() - 2 * i, display.height() - 2 * i, SH110X_WHITE);
    display.display();
    delay(1);
  }
}

void testdrawline() {
  for (int16_t i = 0; i < display.width(); i += 4) {
    display.drawLine(0, 0, i, display.height() - 1, SH110X_WHITE);
    display.display();
    delay(1);
  }
  for (int16_t i = 0; i < display.height(); i += 4) {
    display.drawLine(0, 0, display.width() - 1, i, SH110X_WHITE);
    display.display();
    delay(1);
  }
  delay(250);

  display.clearDisplay();
  for (int16_t i = 0; i < display.width(); i += 4) {
    display.drawLine(0, display.height() - 1, i, 0, SH110X_WHITE);
    display.display();
    delay(1);
  }
  for (int16_t i = display.height() - 1; i >= 0; i -= 4) {
    display.drawLine(0, display.height() - 1, display.width() - 1, i, SH110X_WHITE);
    display.display();
    delay(1);
  }
  delay(250);

  display.clearDisplay();
  for (int16_t i = display.width() - 1; i >= 0; i -= 4) {
    display.drawLine(display.width() - 1, display.height() - 1, i, 0, SH110X_WHITE);
    display.display();
    delay(1);
  }
  for (int16_t i = display.height() - 1; i >= 0; i -= 4) {
    display.drawLine(display.width() - 1, display.height() - 1, 0, i, SH110X_WHITE);
    display.display();
    delay(1);
  }
  delay(250);

  display.clearDisplay();
  for (int16_t i = 0; i < display.height(); i += 4) {
    display.drawLine(display.width() - 1, 0, 0, i, SH110X_WHITE);
    display.display();
    delay(1);
  }
  for (int16_t i = 0; i < display.width(); i += 4) {
    display.drawLine(display.width() - 1, 0, i, display.height() - 1, SH110X_WHITE);
    display.display();
    delay(1);
  }
  delay(250);
}