Patch for Timer 1 and negative time-delta's

ArduinoMetalDetector.ino

@@ -22,102 +22,103 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-// Number of cycles from external counter needed to generate a signal event
-#define CYCLES_PER_SIGNAL 5000
-
-// Base tone frequency (speaker)
-#define BASE_TONE_FREQUENCY 280
-
-// Frequency delta threshold for fancy spinner to trigger
-#define SPINNER_THRESHOLD 700
-
-// Pin definitions
-#define SENSITIVITY_POT_APIN 1
-#define SPEAKER_PIN 2
-#define SPINNER_PIN 9
-#define TRIGGER_BTN_PIN 11
-#define RESET_BTN_PIN 12
-
-unsigned long lastSignalTime = 0;
-unsigned long signalTimeDelta = 0;
-
-boolean firstSignal = true;
-unsigned long storedTimeDelta = 0;
-
-// This signal is called whenever OCR1A reaches 0
-// (Note: OCR1A is decremented on every external clock cycle)
-SIGNAL(TIMER1_COMPA_vect)
-{
-  unsigned long currentTime = micros();
-  signalTimeDelta =  currentTime - lastSignalTime;
-  lastSignalTime = currentTime;
-
-  if (firstSignal)
-  {
-    firstSignal = false;
-  }
-  else if (storedTimeDelta == 0)
-  {
-    storedTimeDelta = signalTimeDelta;
-  }
-
-  // Reset OCR1A
-  OCR1A += CYCLES_PER_SIGNAL;
-}
-
-void setup()
-{
-  // Set WGM(Waveform Generation Mode) to 0 (Normal)
-  TCCR1A = 0b00000000;
-
-  // Set CSS(Clock Speed Selection) to 0b111 (External clock source on T0 pin
-  // (ie, pin 5 on UNO). Clock on rising edge.)
-  TCCR1B = 0b00000111;
-
-  // Enable timer compare interrupt A (ie, SIGNAL(TIMER1_COMPA_VECT))
-  TIMSK1 |= (1 << OCIE1A);
-
-  // Set OCR1A (timer A counter) to 1 to trigger interrupt on next cycle
-  OCR1A = 1;
-
-  pinMode(SPEAKER_PIN, OUTPUT);
-  pinMode(SPINNER_PIN, OUTPUT);
-  pinMode(TRIGGER_BTN_PIN, INPUT_PULLUP);
-  pinMode(RESET_BTN_PIN, INPUT_PULLUP);
-}
-
-void loop()
-{
-  if (digitalRead(TRIGGER_BTN_PIN) == LOW)
-  {
-    float sensitivity = mapFloat(analogRead(SENSITIVITY_POT_APIN), 0, 1023, 0.5, 10.0);
-    int storedTimeDeltaDifference = (storedTimeDelta - signalTimeDelta) * sensitivity;
-    tone(SPEAKER_PIN, BASE_TONE_FREQUENCY + storedTimeDeltaDifference);
-
-    if (storedTimeDeltaDifference > SPINNER_THRESHOLD)
-    {
-      digitalWrite(SPINNER_PIN, HIGH);
-    }
-    else
-    {
-      digitalWrite(SPINNER_PIN, LOW);
-    }
-  }
-  else
-  {
-    noTone(SPEAKER_PIN);
-    digitalWrite(SPINNER_PIN, LOW);
-  }
-
-  if (digitalRead(RESET_BTN_PIN) == LOW)
-  {
-    storedTimeDelta = 0;
-  }
-}
-
-float mapFloat(int input, int inMin, int inMax, float outMin, float outMax)
-{
-  float scale = (float)(input - inMin) / (inMax - inMin);
-  return ((outMax - outMin) * scale) + outMin;
-}
+// Number of cycles from external counter needed to generate a signal event
+// Larger number: Better resolution and longer aquisition time. Max value 65535 (16 bit)
+#define CYCLES_PER_SIGNAL 5000
 
+// Base tone frequency (speaker)
+#define BASE_TONE_FREQUENCY 280
+
+// Frequency delta threshold for fancy spinner to trigger
+#define SPINNER_THRESHOLD 700
+
+// Pin definitions
+#define SENSITIVITY_POT_APIN 1
+#define SPEAKER_PIN 2
+#define SPINNER_PIN 9
+#define TRIGGER_BTN_PIN 11
+#define RESET_BTN_PIN 12
+
+unsigned long lastSignalTime = 0;
+long signalTimeDelta = 0;
+long storedTimeDelta = 0;
+
+// This signal is called when the timer value TCNT1 reaches OCR1A
+// (Note: TCNT1 is incremented on every external clock cycle)
+SIGNAL(TIMER1_COMPA_vect)
+{
+  unsigned long currentTime = micros();
+  signalTimeDelta =  currentTime - lastSignalTime;
+  lastSignalTime = currentTime;
+
+  if (storedTimeDelta == 0)
+  {
+    storedTimeDelta = signalTimeDelta;
+  }
+
+  // Move OCR1A value ahead
+  OCR1A += CYCLES_PER_SIGNAL;
+}
+
+void setup()
+{
+  // Set WGM(Waveform Generation Mode) to 0 (Normal)
+  // Timer runs from 0x00 to 0xFFFF and overruns
+  TCCR1A = 0b00000000;
+
+  // Set CSS(Clock Speed Selection) to 0b111 (External clock source on T0 pin
+  // (ie, pin 5 on UNO). Clock on rising edge.)
+  TCCR1B = 0b00000111;
+
+  // Reset counter and start measuring time
+  TCNT1 = 0;
+  OCR1A = CYCLES_PER_SIGNAL;
+  lastSignalTime = micros();
+
+  // Clear interrupt flag by setting OCF1A high
+  TIFR1 |= (1 << OCF1A);
+
+  // Enable timer compare interrupt A (ie, SIGNAL(TIMER1_COMPA_VECT))
+  TIMSK1 |= (1 << OCIE1A);
+
+  pinMode(SPEAKER_PIN, OUTPUT);
+  pinMode(SPINNER_PIN, OUTPUT);
+  pinMode(TRIGGER_BTN_PIN, INPUT_PULLUP);
+  pinMode(RESET_BTN_PIN, INPUT_PULLUP);
+}
+
+void loop()
+{
+  if (digitalRead(TRIGGER_BTN_PIN) == LOW)
+  {
+    float sensitivity = mapFloat(analogRead(SENSITIVITY_POT_APIN), 0, 1023, 0.5, 10.0);
+    int storedTimeDeltaDifference = storedTimeDelta - signalTimeDelta;
+    unsigned int toneFrequency = BASE_TONE_FREQUENCY + abs(storedTimeDeltaDifference) * sensitivity;
+    tone(SPEAKER_PIN, toneFrequency);
+
+    if (storedTimeDeltaDifference > SPINNER_THRESHOLD)
+    {
+      digitalWrite(SPINNER_PIN, HIGH);
+    }
+    else
+    {
+      digitalWrite(SPINNER_PIN, LOW);
+    }
+  }
+  else
+  {
+    noTone(SPEAKER_PIN);
+    digitalWrite(SPINNER_PIN, LOW);
+  }
+
+  if (digitalRead(RESET_BTN_PIN) == LOW)
+  {
+    storedTimeDelta = 0;
+  }
+}
+
+float mapFloat(int input, int inMin, int inMax, float outMin, float outMax)
+{
+  float scale = (float)(input - inMin) / (inMax - inMin);
+  return ((outMax - outMin) * scale) + outMin;
+}