Introduction to Real-Time Clock

The DS1307 Serial Real-Time Clock may be a low-power, full binary-coded decimal (BCD) clock/calendar plus 56 bytes of NV SRAM. Address and data are transferred serially via a 2-wire, bi-directional bus. The clock/calendar provides seconds, minutes, hours, day, date, month, and year information. the top of the month date is automatically adjusted for months with fewer than 31 days, including corrections for an intercalary year. The clock operates in either the 24-hour or 12-hour format with AM/PM indicator. The DS1307 features a built-in power sense circuit that detects power failures and automatically switches to the battery supply.

This allows the module to retain the time, even when it’s not being powered up by the Arduino. This way, whenever you switch on and off your module, the time doesn’t reset. This module uses I2C communication. this suggests that it communicates with the Arduino using just 2 pins.

Pinout of Real-Time Clock

If you’re using other Arduino boards rather than the Uno, check out what are their SCL and SDA pins.

  • Nano: SDA (A4); SCL(A5)
  • MEGA: SDA (20); SCL(21)
  • Leonardo: SDA (20); SCL(21)
MODULE PIN Arduino Connection
Vcc 5V
GND Ground


  • DS1307 I2C real-time clock chip (RTC).
  • 24C32 32 K I2C EEPROM memories.
  • Using LIR2032 rechargeable lithium battery and charging circuit with.
  • DS1307 with battery backup cannot solve the problem of literacy.
  • Fully charged, can provide DS1307 timing 1 year.
  • Compact design, 27mm * 28mm * 8.4mm.
  • Leads to the DS1307 clock pin provides the clock signal for the microcontroller.


  • To design a real-time clock.
  • DIY projects.
  • Robotics projects.
  • Arduino projects.
  • Raspberry-Pi projects.
  • Electrical/Electronic projects.