FREE SIMULATOR EXAMPLE · INTERMEDIATE

[Pico] I2C RTC Read

This example reads the current time from a virtual DS1307 RTC over the Raspberry Pi Pico’s I2C bus at address 0x68. It requests the seven time registers, converts them from BCD, and prints a formatted time and date to the Serial Monitor once per second.

Board	Raspberry Pi Pico (RP2040 dual-core Cortex-M0+, 133 MHz)
Difficulty	intermediate
Category	communication
Libraries	None — just the Arduino core
Runs in	Sensbench browser simulator — free, no account

The exact circuit you get when you open this example — already wired, ready to run.

The sketch

// Raspberry Pi Pico — I2C DS1307 RTC Read
// Reads time from virtual RTC at address 0x68

#include <Wire.h>

byte bcdToDec(byte val) {
  return ((val >> 4) * 10) + (val & 0x0F);
}

void setup() {
  Serial.begin(115200);
  delay(500);
  Wire.begin();
  Serial.println("=== Pico I2C RTC Read ===");
  Serial.println("Reading DS1307 at 0x68 (system time)");
  Serial.println();
}

void loop() {
  // Set register pointer to 0
  Wire.beginTransmission(0x68);
  Wire.write(0x00);
  Wire.endTransmission();

  // Read 7 bytes: sec, min, hr, dow, date, month, year
  Wire.requestFrom(0x68, 7);
  if (Wire.available() >= 7) {
    byte sec   = bcdToDec(Wire.read() & 0x7F);
    byte min   = bcdToDec(Wire.read());
    byte hr    = bcdToDec(Wire.read() & 0x3F);
    byte dow   = bcdToDec(Wire.read());
    byte date  = bcdToDec(Wire.read());
    byte month = bcdToDec(Wire.read());
    byte year  = bcdToDec(Wire.read());

    const char* days[] = {"", "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"};

    Serial.print("Time: ");
    if (hr < 10) Serial.print('0'); Serial.print(hr); Serial.print(':');
    if (min < 10) Serial.print('0'); Serial.print(min); Serial.print(':');
    if (sec < 10) Serial.print('0'); Serial.print(sec);
    Serial.print("  Date: ");
    Serial.print(days[dow]); Serial.print(' ');
    if (date < 10) Serial.print('0'); Serial.print(date); Serial.print('/');
    if (month < 10) Serial.print('0'); Serial.print(month); Serial.print('/');
    Serial.print("20"); if (year < 10) Serial.print('0'); Serial.println(year);
  } else {
    Serial.println("RTC not responding!");
  }

  delay(1000);
}

How it works

The DS1307 keeps time in seven BCD registers starting at address 0x00: seconds, minutes, hours, day-of-week, date, month, year. The sketch writes 0x00 to set the register pointer, then requests 7 bytes with Wire.requestFrom(0x68, 7) and converts each one from BCD to decimal with the bcdToDec() helper.

The day-of-week byte is used as an index into a day-name array, so the output reads naturally: “Time: 14:03:22 Date: Thu 07/08/2026” style. The 1-second loop delay keeps the display ticking — every second a fresh read of all seven registers.

Before you build it for real

Get the parts

Related examples

FAQ

Why does the code convert BCD to decimal?

The DS1307 stores each digit of the time as 4-bit binary-coded decimal: 0x42 means 42, not 66. The bcdToDec() helper splits the nibbles and reassembles them as a regular number — (val >> 4) * 10 + (val & 0x0F). Skip this step and the clock reads nonsense.

Why mask the seconds with 0x7F and hours with 0x3F?

The DS1307’s register bits are overloaded: bit 7 of the seconds register is the clock-halt flag (CH), and the two high bits of the hours register select 12/24-hour mode. Masking strips those control bits so only the actual time digits survive the BCD conversion.