Меньше точно не бывает! Делаем вольтметр на ATTINY10

uint8_t AD;
uint16_t VOLT;

const uint8_t Init[24] = {
  0xAE,         // Display OFF
  0xA8, 0x1F,   // set multiplex (HEIGHT-1): 0x1F for 128x32, 0x3F for 128x64
  0x22, 0x00, 0x03, // Page min to max
  0x20, 0x01,   // Memory addressing mode 0x00 Horizontal 0x01 Vertical
  0xDA, 0x02,   // Set COM Pins hardware configuration to sequential
  0x8D, 0x14,   // Charge pump enabled
  0xD3, 0x00,   // Display offset to 0
  0x81, 0xFF,   // Set contrast
  0xD9, 0xF1,   // Set pre-charge period
  0xDB, 0x40,   // Set vcom detect
  0x21, 0x00, 0x7F, // Column min to max
  0xAF,  // Display on

};

#define PI2C_SDA    PB0
#define PI2C_SCL    PB1

#define OUT_REG PORTB


#define SDA_ON (OUT_REG |= (1<< PI2C_SDA))
#define SDA_OFF (OUT_REG &= ~(1<< PI2C_SDA))
#define SCL_ON (OUT_REG |= (1<< PI2C_SCL))
#define SCL_OFF (OUT_REG &= ~(1<< PI2C_SCL))

#define SDA_READ (PINB & (1<<PI2C_SDA))



#define ADDR 0b01111000 //OLED Address plus write bit



inline void dly() { //пустая команда
  __asm__("NOP");
};




void setup () {
  ADMUX = 2 << MUX0;              // ADC1 (PB1)
  ADCSRA = 1 << ADEN | 3 << ADPS0; // Enable ADC, 125kHz clock

  DDRB = 3;
  for (uint8_t i = 0; i < 100; i++) dly();
  
  start();
  Tx(ADDR);
  Tx(0x00);
  for (uint8_t i = 0; i < 24; i++)
  {
    Tx(Init[i]);
  }

  stop();

}





void loop(void) {
  uint8_t buffer[8] = {0, 0, 10, 0, 0, 11, 12, 12}; //знаковый буффер на 8 ячеек.
  ADCSRA = ADCSRA | 1 << ADSC;    // Start
  while (ADCSRA & 1 << ADSC);     // Wait while conversion in progress
  AD = ADCL;                    //Читаем АЦП

  VOLT = (AD *47)/10;  //Преобразуем значение АЦП в вольты

 
    buffer[0] = VOLT / 1000;  //первый знак
    buffer[1] = (VOLT % 1000) / 100; //второй знак
    buffer[3] = (VOLT % 100) / 10; //третий знак
    buffer[4] = VOLT % 10;  //четвертый знак

  

  OLED_printB(buffer);  //Выводим буффер


}

const uint8_t OLED_FONT[] PROGMEM = {
  0x7F, 0x41, 0x7F, // 0  0
  0x00, 0x00, 0x7F, // 1  1
  0x79, 0x49, 0x4F, // 2  2
  0x41, 0x49, 0x7F, // 3  3
  0x0F, 0x08, 0x7E, // 4  4
  0x4F, 0x49, 0x79, // 5  5
  0x7F, 0x49, 0x79, // 6  6
  0x03, 0x01, 0x7F, // 7  7
  0x7F, 0x49, 0x7F, // 8  8
  0x4F, 0x49, 0x7F, // 9  9
  0x00, 0x60, 0x00, // .  10
  0x1F, 0x78, 0x1F, // V  11
  0x00, 0x00, 0x00, // -  12
  
};



void OLED_printB(uint8_t *buffer) {
  start();
  Tx(ADDR);
  Tx(0x40);
  for (uint8_t i = 0; i < 8; i++) OLED_printD(buffer[i]); // print buffer
  stop();                          // stop transmission
  
}



uint8_t OLED_stretch(uint8_t b) {
  b  = ((b & 2) << 3) | (b & 1);          // split 2 LSB into the nibbles
  b |= b << 1;                            // double the bits
  b |= b << 2;                            // double them again = 4 times
  return b;                               // return the value
}


void OLED_printD(uint8_t ch) {
  uint8_t i, j, k, b;                     // loop variables
  uint8_t sb[4];                          // stretched character bytes
  ch += ch << 1;                          // calculate position of character in font array
  for (i = 8; i; i--) Tx(0x00);    // print spacing between characters
  for (i = 3; i; i--) {                   // font has 3 bytes per character
    b = OLED_FONT[ch++]; // read character byte
    for (j = 0; j < 4; j++, b >>= 2) sb[j] = OLED_stretch(b); // stretch 4 times
    j = 4; if (i == 2) j = 6;             // calculate x-stretch value
    while (j--) {                      // write several times (x-direction)
      for (k = 0; k < 4; k++) Tx(sb[k]); // the 4 stretched bytes (y-direction)
    }
  }
}

/*  i2c start sequence */
void start() {
  SDA_ON;
  dly();
  SCL_ON;
  dly();
  SDA_OFF;
  dly();
  SCL_OFF;
  dly();
}


/*  i2c stop sequence */
void stop() {
  SDA_OFF;
  dly();
  SCL_ON;
  dly();
  SDA_ON;
  dly();
}

/* Transmit 8 bit data to slave */
bool Tx(uint8_t dat) {
  for (uint8_t i = 0; i < 8; i++) {
    (dat & 0x80) ? SDA_ON : SDA_OFF;
    dat <<= 1;
    dly();
    SCL_ON;
    dly();
    SCL_OFF;
    
  }

  SDA_ON;
  SCL_ON;
  dly();
  bool ack = !SDA_READ;    // Acknowledge bit
  SCL_OFF;
  return ack;
}