First Commit

libraries/DS3231/examples/AlarmInterrupt/AlarmInterrupt.ino

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+/*
+AlarmInterrupt.ino
+Jacob Nuernberg
+08/22
+
+Example on using interrupts with DS3231 alarms.
+
+Hardware setup:
+  Connect DS3231 SQW pin to Arduino interrupt pin 2
+
+Tested on:
+- Arduino UNO
+- Arduino nano
+
+Added to this example:
+
+1. Descriptively named variables to pass parameter values.
+
+2. Modify AlarmBits for Alarm 1 to 0b00001111,
+   for clarity, because Alarm 1 uses only bits 3:0.
+   
+3. Add code to prevent Alarm 2 from interfering with the interrupt,
+   by setting A2Minute to a value that can never match the time
+   and setting AlarmBits to 0b01100000: alarm "when minutes match".
+   Also clear the A2 alarm flag.
+
+David Sparks, September 2022
+*/
+
+#include <DS3231.h>
+#include <Wire.h>
+
+// myRTC interrupt pin
+#define CLINT 2
+
+// Setup clock
+DS3231 myRTC;
+
+// Variables for use in method parameter lists
+byte alarmDay;
+byte alarmHour;
+byte alarmMinute;
+byte alarmSecond;
+byte alarmBits;
+bool alarmDayIsDay;
+bool alarmH12;
+bool alarmPM;
+
+// Interrupt signaling byte
+volatile byte tick = 1;
+
+void setup() {
+    // Begin I2C communication
+    Wire.begin();
+
+    // Begin Serial communication
+    Serial.begin(9600);
+    while (!Serial);
+    Serial.println();
+    Serial.println("Starting Serial");
+
+    // Assign parameter values for Alarm 1
+    alarmDay = 0;
+    alarmHour = 0;
+    alarmMinute = 0;
+    alarmSecond = 0;
+    alarmBits = 0b00001111; // Alarm 1 every second
+    alarmDayIsDay = false;
+    alarmH12 = false;
+    alarmPM = false;    
+
+    // Set alarm 1 to fire at one-second intervals
+    myRTC.turnOffAlarm(1);
+    myRTC.setA1Time(
+       alarmDay, alarmHour, alarmMinute, alarmSecond,
+       alarmBits, alarmDayIsDay, alarmH12, alarmPM);
+    // enable Alarm 1 interrupts
+    myRTC.turnOnAlarm(1);
+    // clear Alarm 1 flag
+    myRTC.checkIfAlarm(1);
+
+    // When using interrupt with only one of the DS3231 alarms, as in this example,
+    // it may be advisable to prevent the other alarm entirely,
+    // so it will not covertly block the outgoing interrupt signal.
+
+    // Prevent Alarm 2 altogether by assigning a 
+    // nonsensical alarm minute value that cannot match the clock time,
+    // and an alarmBits value to activate "when minutes match".
+    alarmMinute = 0xFF; // a value that will never match the time
+    alarmBits = 0b01100000; // Alarm 2 when minutes match, i.e., never
+    
+    // Upload the parameters to prevent Alarm 2 entirely
+    myRTC.setA2Time(
+        alarmDay, alarmHour, alarmMinute,
+        alarmBits, alarmDayIsDay, alarmH12, alarmPM);
+    // disable Alarm 2 interrupt
+    myRTC.turnOffAlarm(2);
+    // clear Alarm 2 flag
+    myRTC.checkIfAlarm(2);
+
+    // NOTE: both of the alarm flags must be clear
+    // to enable output of a FALLING interrupt
+
+    // attach clock interrupt
+    pinMode(CLINT, INPUT_PULLUP);
+    attachInterrupt(digitalPinToInterrupt(CLINT), isr_TickTock, FALLING);
+
+    // Use builtin LED to blink
+    pinMode(LED_BUILTIN, OUTPUT);
+}
+
+void loop() {
+    // static variable to keep track of LED on/off state
+    static byte state = false;
+
+    // if alarm went of, do alarm stuff
+    if (tick) {
+        tick = 0;
+        state = ~state;
+        digitalWrite(LED_BUILTIN, state);
+
+        // optional serial output
+        Serial.print("Turning LED ");
+        Serial.println((state ? "ON" : "OFF"));
+
+        // Clear Alarm 1 flag
+        myRTC.checkIfAlarm(1);
+    }
+
+    // Loop delay to emulate other running code
+    delay(10);
+}
+
+
+void isr_TickTock() {
+    // interrupt signals to loop
+    tick = 1;
+    return;
+}