``````/*
Digital Clock using Franzininho, 74HC595, 7 Segment Display (4 digits) and DS1307 RTC
Code by: Uri Shaked
Diagram: Anderson Costa
Visit https://wokwi.com to learn about the Wokwi Simulator
Visit https://franzininho.com.br to learn about the Franzininho
*/
#include <TinyWireM.h>

#define DATA_PIN    5    // Pin connected to DS of 74HC595
#define LATCH_PIN   3    // Pin connected to STCP of 74HC595
#define CLOCK_PIN   4    // Pin connected to SHCP of 74HC595

// How many of the shift registers (74HC595)
#define NUM_SHIFT_REGS 2

const uint8_t numOfRegisterPins = NUM_SHIFT_REGS * 8;

const uint16_t digitMask = 0b1100100001101100;
const uint16_t colonPin = 12;

uint16_t registers = 0;

uint8_t time[4] = {0, 0, 0, 0};

uint8_t digitPins[] = {4, 7, 10, 13}; // 1-Q4, 1-Q7, 2-Q2, 2-Q5

uint16_t digits[] = {
0b0100000000000000, // 0
0b0100000001101100, // 1
0b1000000001000000, // 2
0b0000000001001000, // 3
0b0000000000101100, // 4
0b0000100000001000, // 5
0b0000100000000000, // 6
0b0100000001001100, // 7
0b0000000000000000, // 8
0b0000000000001100, // 9
};

uint8_t seconds;
uint8_t minutes;
uint8_t hours;

bool colon = false;

void setup() {
// Setup TinyWire I2C
TinyWireM.begin();

// Set pins to output
pinMode(DATA_PIN, OUTPUT);
pinMode(CLOCK_PIN, OUTPUT);
pinMode(LATCH_PIN, OUTPUT);
}

void loop() {
scanDigit(1);
scanDigit(2);
scanDigit(3);
scanDigit(4);
updateClock();
}

void updateClock()
{
TinyWireM.beginTransmission(DS1307_ADDR); // Reset DS1307 register pointer
TinyWireM.send(0x00);
TinyWireM.endTransmission();

// Request 7 bytes from DS1307

seconds = bcdToDec(TinyWireM.receive() & 0x7F);

time[0] = hours / 10;
time[1] = hours % 10;
time[2] = minutes / 10;
time[3] = minutes % 10;

colon = seconds & 1 ? HIGH : LOW;
}

void scanDigit(int index)
{
registers = digits[time[index - 1]] | bit(digitPins[index - 1]);
if (colon) {
registers |= bit(colonPin);
}
writeRegisters();
}

void writeRegisters()
{
// Set and display registers
digitalWrite(LATCH_PIN, LOW);
shiftOut(DATA_PIN, CLOCK_PIN, MSBFIRST, highByte(registers));
shiftOut(DATA_PIN, CLOCK_PIN, MSBFIRST, lowByte(registers));
digitalWrite(LATCH_PIN, HIGH);
}

// Convert binary coded decimal to normal decimal numbers
uint8_t bcdToDec(uint8_t value) {
return ((value / 16 * 10) + (value % 16));
}
``````