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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    32 Discussions


    5 weeks ago

    Thanks for the Lib.... seem to work ok for me. Thumps-up from here.

    1 reply

    Theres an error in LowPower if you have a Mega2560, and Compiler 1.8.x

    But that's not your fault ..but a guy called "rocketscream" who's not updating his LowPower code.

    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

    1 reply

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

    4 replies

    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.

    need to rename it as '-' are not accepted

    LowPower lib cannot be added

    Thanks for sharing this.
    Why do you connect the 5v output of the regulator to the nano Vin to and not the 5V input ? Officially, Vin accepts from 7v to 12v.

    1. how can this be set to trigger every hour?

    2. why does it not compile for Atmega168 but ok for Atmega 328?

    4 replies

    Seeing as it appears to be very similar to the one here, I think change the

    RTC.setAlarm(ALM1_MATCH_HOURS, 33, 18, 0); //set your wake-up time here

    line to

    RTC.setAlarm(ALM1_MATCH_MINUTES, 18, 0); //set your wake-up time here

    where the 18 and 0 are minutes and seconds respectively.

    Correction to your code:

    RTC.setAlarm(ALM1_MATCH_MINUTES, 0, 18, 0, 0); //set your wake-up time here

    where first enter seconds, then minutes, then hours, then days. These must be entered if not you get compilation error.

    Wrong: first seconds then minutes.

    RTC.setAlarm(ALM1_MATCH_MINUTES, 0, 18); //set your wake-up time here

    where the 18 and 0 are minutes and seconds respectively

    Hi, thank you for that! I will try that code.

    About not compiling using Atmega168, I found out that the library does not recognise the deep sleep function for Atmega168. This is sleep_mode_extended_standby not recognised by LowPower.h which is solved by

    Atmega168P does use this extended standby, using above solution it does compile correctly for Atmega168P.