Replace delay() with ISR_Timer

button.ino

@@ -1,11 +1,22 @@
 volatile unsigned long lastButtonPress = millis();
 
+void initButton() {
+  pinMode(BUTTON_PIN, INPUT_PULLUP);
+  // Order of ISRs matter: RISING should be invoked first
+  attachInterrupt(digitalPinToInterrupt(BUTTON_PIN), buttonISRtime, CHANGE);
+  attachInterrupt(digitalPinToInterrupt(BUTTON_PIN), buttonISRstate, RISING);  
+}
+
 void buttonISRstate() {
   if ((millis() - lastButtonPress) > 100) {
-    if (countdown > 0)
+    if (countdown < 0)
       countdown = 0;
-    else
-      countdown = BREAK_LENGTH;
+    else if (countdown == 0)
+      countdown = COUNTDOWN;
+    else {
+      countdown = -1;
+      digitalWrite(BUTTON_LED_PIN, LOW);
+    }
   }
 }
 

metronom.ino

@@ -5,44 +5,41 @@
 SAMDTimer ITimer(TIMER_TC3);
 SAMD_ISR_Timer ISR_Timer;
 
-void TimerHandler(void) {
-  ISR_Timer.run();
-}
+void TimerHandler(void) { ISR_Timer.run(); }
 
+const int COUNTDOWN = 300;
+const int PERIOD_MS = 1000;
 
+const uint BUTTON_PIN = 6;
+const uint BUTTON_LED_PIN = 5;
 const uint BUZZER_PIN = 0;
 
-const uint BUTTON_LED_PIN = 5;
-const uint BUTTON_PIN = 6;
-
-const int BREAK_LENGTH = 300000;
-const int BREAK_STEP = 2000;
-
-volatile int countdown = 0;
-int step;
+/* Metronome state is expressed by countdown:
+ *  -1 - IDLE
+ *   0 - BEATING
+ *  >0 - COUNTDOWN
+ */
+volatile int countdown = -1;
 
 void setup() {
-  pinMode(BUTTON_PIN, INPUT_PULLUP);
-  // Order of ISRs matter: RISING should be invoked first
-  attachInterrupt(digitalPinToInterrupt(BUTTON_PIN), buttonISRtime, CHANGE);
-  attachInterrupt(digitalPinToInterrupt(BUTTON_PIN), buttonISRstate, RISING);
+  initButton();
 
-  initTemperature();
   ITimer.attachInterruptInterval_MS(10, TimerHandler);
-  ISR_Timer.setInterval(1000, readTemperature);
+  ISR_Timer.setInterval(PERIOD_MS, metronomeBeat);
+  ISR_Timer.setInterval(PERIOD_MS, metronomeCountdown);
 }
 
-void loop() {
+void metronomeCountdown() {
   if (countdown > 0) {
-    step = min(BREAK_STEP, countdown);
-    countdown -= step;
-    
-    digitalWrite(BUTTON_LED_PIN, HIGH);
-    delay(min(BREAK_STEP/2, step));
-    digitalWrite(BUTTON_LED_PIN, LOW);
-    delay(max(step-BREAK_STEP/2, 0));
-  } else {
-    tone(BUZZER_PIN, 1000, 100);
-    delay(1000);
+    countdown -= 1;
+
+    digitalWrite(BUTTON_LED_PIN, countdown % 2 ? HIGH : LOW);
   }
 }
+
+void metronomeBeat() {
+  if (countdown == 0)
+    tone(BUZZER_PIN, 1000, 100);
+}
+
+void loop() {}

temperature.ino

@@ -1,21 +0,0 @@
-#include "grove_alphanumeric_display.h"
-#include "Seeed_BME280.h"
-
-Seeed_Digital_Tube tube;
-BME280 sensor;
-
-void initTemperature() {
-  // BME280 inits Wire
-  sensor.init();
-  
-  tube.setTubeType(TYPE_4, TYPE_4_DEFAULT_I2C_ADDR);
-  tube.setBrightness(15);
-  tube.setBlinkRate(BLINK_OFF);
-  tube.setPoint(true,true);
-}
-
-void readTemperature() {
-  char temperature_str[5];
-  sprintf(temperature_str, "%4u", (unsigned int) (sensor.getTemperature() * 100.0));
-  tube.displayString(temperature_str);
-}