// Frequency timer
// Author: Nick Gammon
// Date: 10th February 2012
// Input: Pin D2
volatile boolean first;
volatile boolean triggered;
volatile unsigned long overflowCount;
volatile unsigned long startTime;
volatile unsigned long finishTime;
// here on rising edge
void isr ()
{
unsigned int counter = TCNT1; // quickly save it
// wait until we noticed last one
if (triggered)
return;
if (first)
{
startTime = (overflowCount << 16) + counter;
first = false;
return;
}
finishTime = (overflowCount << 16) + counter;
triggered = true;
detachInterrupt(0);
} // end of isr
// timer overflows (every 65536 counts)
ISR (TIMER1_OVF_vect)
{
overflowCount++;
} // end of TIMER1_OVF_vect
void prepareForInterrupts ()
{
// get ready for next time
EIFR = bit (INTF0); // clear flag for interrupt 0
first = true;
triggered = false; // re-arm for next time
attachInterrupt(0, isr, RISING);
} // end of prepareForInterrupts
void setup ()
{
Serial.begin(115200);
Serial.println("Frequency Counter");
// reset Timer 1
TCCR1A = 0;
TCCR1B = 0;
// Timer 1 - interrupt on overflow
TIMSK1 = bit (TOIE1); // enable Timer1 Interrupt
// zero it
TCNT1 = 0;
overflowCount = 0;
// start Timer 1
TCCR1B = bit (CS20); // no prescaling
// set up for interrupts
prepareForInterrupts ();
} // end of setup
void loop ()
{
if (!triggered)
return;
unsigned long elapsedTime = finishTime - startTime;
float freq = F_CPU / float (elapsedTime); // each tick is 62.5 nS at 16 MHz
Serial.print ("Took: ");
Serial.print (elapsedTime);
Serial.print (" counts. ");
Serial.print ("Frequency: ");
Serial.print (freq);
Serial.println (" Hz. ");
// so we can read it
delay (500);
prepareForInterrupts ();
} // end of loop
In void setup:
TCCR1B = bit (CS20); // no prescaling,
The error is that CS20 is in TCCR2B, not 1B.
Because we have used TCCR1B = 0 in a previous step, to stablish any prescaling in TCCR1B, CS10, CS11, and CS12 should be used.
update moderatore: removed snippet to make question more explicit