How to Use DeadOn RTC - DS3234 Breakout: Examples, Pinouts, and Specs

The DeadOn RTC - DS3234 Breakout (manufacturer part ID: BOB-10160) by SparkFun Electronics is a highly accurate real-time clock (RTC) module based on the DS3234 chip. This module is designed to provide precise timekeeping and includes a battery backup to maintain time even during power outages. It communicates with microcontrollers via the SPI interface, making it suitable for a wide range of applications.

In addition to timekeeping, the DS3234 chip offers advanced features such as programmable alarms, temperature sensing, and a 256-byte SRAM for user data storage. These features make the DeadOn RTC ideal for projects requiring reliable timekeeping and additional functionality.

• Data logging systems
• Time-stamped event recording
• Alarm systems
• Industrial automation
• IoT devices requiring precise time synchronization

The DeadOn RTC breakout board has the following pin layout:

1. Power Supply: Connect the VCC pin to a 3.3V or 5V power source and the GND pin to ground.
2. SPI Communication: Connect the CS, SCK, MOSI, and MISO pins to the corresponding SPI pins on your microcontroller.
3. Battery Backup: Insert a CR1225 coin cell battery into the battery holder to maintain timekeeping during power outages.
4. Interrupts and Alarms: Use the INT/SQW pin to trigger interrupts or output a square wave signal, as configured in the DS3234 registers.
5. Optional Outputs: The 32kHz pin can be used to output a 32kHz clock signal if needed.

• Ensure the SPI clock speed does not exceed the DS3234's maximum supported frequency (20 MHz).
• Use pull-up resistors on the SPI lines if required by your microcontroller.
• Configure the DS3234 registers carefully to set alarms, enable the square wave output, or access the SRAM.
• Avoid shorting the battery backup terminals to prevent damage to the module.
• For long-term accuracy, consider calibrating the RTC using the temperature compensation feature.

Below is an example of how to interface the DeadOn RTC with an Arduino UNO using the SPI library:

#include <SPI.h>

// Define SPI pins for the DS3234 RTC
#define CS_PIN 10  // Chip Select pin connected to Arduino pin 10

void setup() {
  Serial.begin(9600);  // Initialize serial communication
  SPI.begin();         // Initialize SPI communication
  pinMode(CS_PIN, OUTPUT);
  digitalWrite(CS_PIN, HIGH);  // Set CS pin HIGH to deselect the RTC

  // Initialize the RTC
  rtcWriteRegister(0x0E, 0x00);  // Disable alarms and square wave output
  Serial.println("RTC Initialized");
}

void loop() {
  // Read the current time from the RTC
  digitalWrite(CS_PIN, LOW);  // Select the RTC
  SPI.transfer(0x00);         // Send address to read seconds register
  byte seconds = SPI.transfer(0x00);  // Read seconds
  digitalWrite(CS_PIN, HIGH); // Deselect the RTC

  // Print the time to the Serial Monitor
  Serial.print("Seconds: ");
  Serial.println(seconds & 0x7F);  // Mask the highest bit (clock halt bit)
  delay(1000);  // Wait for 1 second
}

// Function to write to a DS3234 register
void rtcWriteRegister(byte reg, byte value) {
  digitalWrite(CS_PIN, LOW);  // Select the RTC
  SPI.transfer(reg | 0x80);  // Set the write bit (MSB = 1)
  SPI.transfer(value);       // Write the value to the register
  digitalWrite(CS_PIN, HIGH); // Deselect the RTC
}

1. RTC Not Responding Over SPI:

   • Ensure the CS, SCK, MOSI, and MISO pins are correctly connected.
   • Verify that the SPI clock speed is within the DS3234's limits (≤20 MHz).
   • Check for loose connections or soldering issues on the breakout board.

2. Time Resets After Power Loss:

   • Confirm that a CR1225 coin cell battery is installed in the battery holder.
   • Ensure the battery voltage is within the recommended range (2.3V to 3.7V).

3. Incorrect Time or Date:

   • Verify that the time and date were set correctly in the DS3234 registers.
   • Check for software bugs in your code that might overwrite the RTC settings.

4. Interrupts or Alarms Not Triggering:

   • Ensure the INT/SQW pin is connected to the correct interrupt pin on your microcontroller.
   • Double-check the alarm configuration in the DS3234 registers.

Q: Can the DeadOn RTC operate without a battery?
A: Yes, the RTC will function without a battery as long as it is powered by VCC. However, the time will reset if power is lost.

Q: How accurate is the DS3234 RTC?
A: The DS3234 has an accuracy of ±2 ppm (±0.17 seconds/day) at 0°C to +40°C, making it highly precise for most applications.

Q: Can I use the DeadOn RTC with a 3.3V microcontroller?
A: Yes, the module is compatible with both 3.3V and 5V systems.

Q: What is the purpose of the 256-byte SRAM?
A: The SRAM can be used to store user data that needs to be retained while the RTC is powered.

This concludes the documentation for the DeadOn RTC - DS3234 Breakout. For further assistance, refer to the SparkFun product page or the DS3234 datasheet.