RTC

Real Time Clock alarms and interrupts and sleep examples

RTC and Low Power Functionality

The OPEnS Lab currently supports sleep functionality for both the Adafruit Feather M0 and the Adafruit Feather 32u4. The RTC used to wake both the M0 and the 32u4 is the Adafruit DS3231 Precision RTC Breakout.

RTC and Low Power Dependencies

• DS3231 Extended Library
• Low Power Library
• Enable Interrupt

NOTE: To use the DS3231 extended library with the Feather M0, the following line must be added to RTClibExtended.h:

#define _BV(bit) (1 << (bit))

Sleep Modes

Project Loom supports two sleep modes for the Feather M0 and one sleep mode for the Feather 32u4. Here are some details on the various modes:

Mode	Supported board	Current Draw
Idle_2	Feather M0	~5 mA
Standby	Feather M0	~0.7 mA
SLEEP_FOREVER	Feather 32U4	Untested

Standby Operation

Due to some incompatibilities between Standby mode and falling interrupts, a very particular scheme must be followed to use Standby mode on the Feather M0. The following code is an example of how standby mode can be set up on the M0 with a wakeup interrupt on pin 11:

void setup() {
    pinMode(11, INPUT_PULLUP);
    bool OperationFlag = false;
    delay(10000); //It's important to leave a delay so the board can more easily
                  //be reprogrammed
}

void loop() {
    if (OperationFlag) {

        // Whatever you want the board to do while awake goes here

        OperationFlag = false; //reset the flag
    }

    attachInterrupt(digitalPinToInterrupt(11), wake, LOW);

    LowPower.standby();
}

void wake() {
    OperationFlag = true;
    detachInterrupt(digitalPinToInterrupt(11)); //detach the interrupt in the ISR so that
                                                //multiple ISRs are not called
}