Real Time Clock Module


Arduino Tiny RTC I2C Real Time Clock

This Arduino Tiny RTC I2C module incorporates the DS1307 I2C real time clock IC and the 24C32 32K I2C EEPROM storage. What's more, it has a DS18B20 temperature sensor on board. All of this in a tiny package of 25mm x 28mm x 8.4mm. It comes with a LIR2303 rechargeable lithium battery, and a charging circuit is included in the module. When the temperature sensor is off, the RTC module can run for 1 year on a single charge.

This module is used for applications such as datalogging, timing applications ex. turning on the sprinkers at 4pm in the evenings. Since the module is self powered the time data is maintained even if the Arduino is powered off, allowing for building low power systems which can run for a long span of time without change of batteries.

Specs of DS18B20 Temperature Sensor

  • 3.0-5.5V input voltage
  • Waterproof
  • -55°C to+125°C temperature range
  • ±0.5°C accuracy from -10°C to +85°C
  • 1 Wire interface

Wiring the RTC to Arduino

arduino to RTC

The most useful pins are duplicated from P1 to P2. If needed, the pin "BAT" can be fed into an ADC pin for monitoring the battery voltage. The pin-outs are explained below. Connecting "VCC" to 5 V will trickle charge the onboard battery.

Arduino Tiny RTC I2C Real Time Clock Pinout

PIN Description Comment
BAT Battery voltage To monitor the battery voltage, or not connected
GND Ground Ground
VCC 5V supply Power the module and charge the battery
SDA I2C data I2C data for the RTC
SCL I2C clock I2C clock for the RTC
DS DS18B20 Temp. Sensor output One wire inteface
SQ Square wave output Normally not used

The I2C wires "SDA" and "SCL" are the data line and clock line, they should be connected to the corresponding pins depending on the Arduino board.

Board I2C / TWI pins
Uno, Ethernet A4 (SDA), A5 (SCL)
Mega2560 20 (SDA), 21 (SCL)
Leonardo 2 (SDA), 3 (SCL)
Due 20 (SDA), 21 (SCL), SDA1, SCL1

Example code is available here.

For more detail, please visit the Arduino Wire Library.


The schematics of this RTC module can be downloaded here.



Price: $17.99
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