Arduino Sleep and Wakeup Test With DS3231 RTC





Introduction: Arduino Sleep and Wakeup Test With DS3231 RTC

I made this circuit for testing the sleep and wakeup features of Arduino using an external interrupt produced by a DS3231 real time clock with a programmed alarm. This feature is very useful when you want your Arduino project to run on batteries because sending the Arduino to sleep mode greatly reduces power consumption and extends the battery life.

For doing this I used a custom DS3231 library for Arduino (that I called RTClibExtended) that I produced modifying an existing library RTClib by Adafruit, which did not include the functionalities for programming alarms. You can download this library from

In my sketch I also use the Low-Power library for programming the sleep mode, that you can download from

Parts list:

- Arduino (I used the Nano version for this project)

- A 9 Volts battery

- LM2596S Step-down voltage regulator, for reducing the power voltage to 5 Volts

- DS3231 module

Step 1: Connect All Parts

Connect all parts as indicated in the figure.

The Voltage regulator is a variable one: adjust the output voltage to 5 Volts before connecting the power to other components.

Step 2: Install the Libraries

Download the RTClibExtended and Low-Power libraries and install them in your Arduino library.

Step 3: The Sketch

Copy and past or download the sketch.

It programs an alarm on the DS3231 clock at a given time every day. Change the time for your test, compile the sketch and load it. The sketch is fully commented to explain what is done.

The test uses the on-board led on Arduino for evidencing the activity status.

When the sketch starts, the led should lit up for 1 second, to signal that it started correctly, than Arduino should enter the sleep mode: the led is set to OFF for indicating this.

At the programmed time, the DS3231 will produce an interrupt on the SQW pin connected to the Arduino D2 pin (which goes from the HIGH to the LOW level) which will wake up the Arduino from the sleep state, and the led should start to blink to indicate this.

You may use this feature in your projects.




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    1 Questions

    how can I retrieve the date and time of the rtc ?

    DateTime now =;
    Serial.print(now.year(), DEC);
    Serial.print(now.month(), DEC);
    Serial.print(, DEC);
    Serial.print(" (");
    Serial.print(") ");
    Serial.print(now.hour(), DEC);
    Serial.print(now.minute(), DEC);
    Serial.print(now.second(), DEC);


    RTC.setAlarm(ALM1_MATCH_HOURS, 33, 18, 0); //set your wake-up time here
    isn't it 0:18:33 ? instead of 18:33

    How do you get this back to sleep after the wake-up?

    You have to set arduino in sleep mode again.

    And how do you achieve that in your code?

    You can use the LowPower library and the powerDown method. You can find lots of examples on internet.

    please can you upload a complete example ?

    LowPower lib is corrupted

    need to rename it as '-' are not accepted

    LowPower lib cannot be added