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/******* Sketch to test Input Capture interrupt handling *********************************
functionality: measure length of pulses on the ICP pin with precision of 0.5 microseconds
Show the min and max pulse widths in microseconds on the serial port

**************************************************************************************************************/
#include <stdio.h>      // for verbose debugging using sprintf 

#define icpPin 8        // ICP input pin on arduino
#define outPin 2        // output pin that will shadow the input, can be monitored with a scope 

                       // some variables to help see that something is happening in the interrupt handlers
volatile unsigned int Value;     // this stores the current ICR1 value
volatile unsigned int MinValue;     
volatile unsigned int MaxValue;
volatile unsigned int Overflows;
volatile unsigned int PulseCount;


/* Overflow interrupt vector */
ISR(TIMER1_OVF_vect){                 // here if no input pulse detected 
  Overflows++;                       // incriment overflow count  
}

/* ICR interrupt vector */
ISR(TIMER1_CAPT_vect){
  TCNT1 = 0;                            // reset the counter  
  if( bit_is_set(TCCR1B ,ICES1)){       // was rising edge detected ?   
       digitalWrite(outPin,HIGH );      // yes, set our output pin high to mirror the input
  }
  else {                                // falling edge was detected 
       Value = ICR1;                    // save the input capture value 
       digitalWrite(outPin,LOW );       // set our output pin low to mirror the input  
       PulseCount++;
       if(Value < MinValue)             // update min or max values as appropriate   
           MinValue = Value;
       if (Value > MaxValue)
           MaxValue = Value;    
  }     
  TCCR1B ^= _BV(ICES1);                 // toggle bit value to trigger on the other edge    
}

void setup() {
 Serial.begin(19200);
 pinMode(outPin, OUTPUT);               // declare the ledPin as an OUTPUT
 pinMode(icpPin, INPUT);                // ICP pin (digital pin 8 on arduino) as input
 MinValue =    30000;                   // Initialise with extreme values 
 MaxValue =    0;


 TCCR1A = 0 ;                    // this register set to 0!
 TCCR1B =_BV(CS11);              // NORMAL MODE!!, prescaller 8, rising edge ICP1 - this works
 TCCR1B |= _BV(ICES1);           // enable input capture     

 TIMSK1 =  _BV(ICIE1);                         // enable input capture interrupt for timer 1
 TIMSK1 |= _BV(TOIE1);                         // enable overflow interrupt to detect missing input pulses 
 Serial.print("Finished setup\r\n");
}

// this loop prints the number of pulses in the last second, showing min and max pulse widths 
void loop() {
 char buffer[80];
 // show the captured data, divide pulse widths by 2 to display time in microseconds
 sprintf(buffer,"Got %d pulses: min=%d, max=%d (%d timer overflows)\r\n", PulseCount, MinValue / 2, MaxValue / 2, Overflows);         
 Serial.print(buffer);    // send the info to the serial port
 /* reset variables ready for the next reading */   
 PulseCount = Overflows = 0; // reset counts
 MinValue =    30000;        // set values to extremes
 MaxValue =    0;       
  
 delay(1000);             // wait 1 second for next update  [/font]            
}