How to Use DS1302 RTC: Examples, Pinouts, and Specs

The DS1302 Real-Time Clock (RTC) is a widely used electronic component that provides accurate timekeeping and date information in a binary-coded decimal (BCD) format. It includes a built-in clock/calendar and 31 bytes of static RAM. The DS1302 communicates with microcontrollers via a simple serial interface and is commonly used in embedded systems, clocks, data loggers, and other devices that require timekeeping functionality.

• Digital clocks and watches
• Data logging systems
• Time-stamping events
• Embedded systems requiring scheduled operations

• Voltage Supply: 2.0V to 5.5V
• Timekeeping Current: <1µA (typical at 2.0V)
• Interface: Serial (Simple 3-wire interface)
• Clock Format: HH:MM:SS (24-hour format)
• Calendar Format: YY-MM-DD-dd (Year, Month, Date, Day)
• Leap Year Compensation: Valid up to 2100

1. Power Supply: Connect the Vcc pin to a 2.0V to 5.5V power source and the GND pin to the ground.
2. Crystal Oscillator: Attach a 32.768 kHz crystal oscillator to pins X1 and X2.
3. Microcontroller Interface: Connect the SCLK, I/O, and CE pins to the corresponding digital I/O pins on your microcontroller.
4. Backup Battery: To maintain timekeeping when the main power is off, connect a 3V coin cell battery to the Vbat pin.

• Ensure that the power supply voltage is within the specified range to avoid damaging the DS1302.
• The backup battery should be non-rechargeable to prevent charging from the Vcc supply.
• Keep the crystal and DS1302 as close as possible to minimize noise and ensure accurate timekeeping.
• Use pull-up resistors on the I/O lines if required by your microcontroller's specifications.

#include <DS1302.h>

// Initialize the DS1302
// CE pin -> Arduino Digital 2, I/O pin -> Arduino Digital 3, SCLK pin -> Arduino Digital 4
DS1302 rtc(2, 3, 4);

void setup() {
  Serial.begin(9600);
  rtc.halt(false);  // Enable the clock
  rtc.writeProtect(false);  // Disable write protection

  // Set the time to 12:00:00 (24hr format), date to 2023-04-01
  rtc.setDOW(SATURDAY);        // Set Day-of-Week to Saturday
  rtc.setTime(12, 0, 0);       // Set the time to 12:00:00 (24hr format)
  rtc.setDate(1, 4, 2023);     // Set the date to April 1, 2023
}

void loop() {
  // Print the current date and time to the Serial Monitor
  Serial.print(rtc.getDOWStr());
  Serial.print(" ");
  Serial.print(rtc.getDateStr());
  Serial.print(" -- ");
  Serial.println(rtc.getTimeStr());

  // Wait one second before repeating
  delay(1000);
}

• Incorrect Timekeeping: Ensure the crystal oscillator is properly connected and not damaged.
• Communication Errors: Check the wiring between the DS1302 and the microcontroller, and ensure that the correct pins are used.
• Battery Issues: If the time resets after power loss, verify that the backup battery is correctly installed and has sufficient voltage.

• Double-check all connections and ensure that solder joints are solid and not causing intermittent connections.
• Verify that the microcontroller's I/O pins are configured correctly for communication with the DS1302.
• If using a library, ensure that it is compatible with your version of the Arduino IDE and the microcontroller.

Q: Can the DS1302 be used in a 12-hour format? A: Yes, the DS1302 can be configured to use a 12-hour format with an AM/PM indicator.

Q: How long will the backup battery last? A: The backup battery life depends on the battery capacity and the quality of the battery. Typically, a 3V coin cell battery can last several years.

Q: Is the DS1302 Y2K compliant? A: Yes, the DS1302 has leap year compensation and is valid up to the year 2100.