Meranie dĺžky impulzu 2

Toto je staršia verzia, ktorú sme mali na cvičeniach kedysi dávno.

Literatúra

• AVR130: Setup and Use the AVR® Timers. Aplication Note, Atmel Corporation 2002.
  + software download
• AVR135: Using Timer Capture to Measure PWM Duty Cycle. Aplication Note, Atmel Corporation 2005.
  + software download

Príklad (avrdemo7.hex)

Na vstupe ICP1 (na doske Acrob D8, na čipe ATmega328P je to PB0, pin 14) máme pripojený zdroj externého kmitočtu cca 1Hz:

Nastavené máme spúšťanie ICR dobežnou hranou, počítadlo počíta 16 MHz:1024, vypisujeme niekoľkokrát za sekundu stavy všetkých registrov

Input D8 = 1  TCNT1 =   353  ICR =     0 
Input D8 = 1  TCNT1 =  1543  ICR =     0 
Input D8 = 1  TCNT1 =  2749  ICR =     0 
Input D8 = 1  TCNT1 =  3956  ICR =     0 
Input D8 = 1  TCNT1 =  5163  ICR =     0 
Input D8 = 0  TCNT1 =  6369  ICR =  6070  D = 6070  T = 388.4800 ms
Input D8 = 0  TCNT1 =  7706  ICR =  6070  
Input D8 = 0  TCNT1 =  8961  ICR =  6070  
Input D8 = 0  TCNT1 = 10216  ICR =  6070  
Input D8 = 0  TCNT1 = 11488  ICR =  6070  
Input D8 = 0  TCNT1 = 12759  ICR =  6070  
Input D8 = 1  TCNT1 = 14031  ICR =  6070  
Input D8 = 1  TCNT1 = 15303  ICR =  6070  
Input D8 = 1  TCNT1 = 16574  ICR =  6070  
Input D8 = 1  TCNT1 = 17846  ICR =  6070  
Input D8 = 1  TCNT1 = 19117  ICR =  6070  
Input D8 = 1  TCNT1 = 20389  ICR =  6070  
Input D8 = 1  TCNT1 = 21661  ICR = 21591  D = 15521  T = 993.3441 ms
Input D8 = 0  TCNT1 = 23046  ICR = 21591  
Input D8 = 0  TCNT1 = 24334  ICR = 21591  
Input D8 = 0  TCNT1 = 25622  ICR = 21591  
Input D8 = 0  TCNT1 = 26910  ICR = 21591  
Input D8 = 0  TCNT1 = 28197  ICR = 21591  
Input D8 = 1  TCNT1 = 29485  ICR = 21591  
Input D8 = 1  TCNT1 = 30773  ICR = 21591  
Input D8 = 1  TCNT1 = 32061  ICR = 21591  
Input D8 = 1  TCNT1 = 33349  ICR = 21591  
Input D8 = 1  TCNT1 = 34636  ICR = 21591  
Input D8 = 1  TCNT1 = 35924  ICR = 21591  
Input D8 = 1  TCNT1 = 37212  ICR = 37110  D = 15519  T = 993.2161 ms
Input D8 = 0  TCNT1 = 38597  ICR = 37110  
Input D8 = 0  TCNT1 = 39885  ICR = 37110  
Input D8 = 0  TCNT1 = 41173  ICR = 37110  
Input D8 = 0  TCNT1 = 42461  ICR = 37110  
Input D8 = 0  TCNT1 = 43749  ICR = 37110  
Input D8 = 1  TCNT1 = 45037  ICR = 37110  
Input D8 = 1  TCNT1 = 46324  ICR = 37110  
Input D8 = 1  TCNT1 = 47612  ICR = 37110  
Input D8 = 1  TCNT1 = 48900  ICR = 37110  
Input D8 = 1  TCNT1 = 50188  ICR = 37110  
Input D8 = 1  TCNT1 = 51476  ICR = 37110  
Input D8 = 1  TCNT1 = 52763  ICR = 52630  D = 15520  T = 993.2800
Input D8 = 0  TCNT1 = 54149  ICR = 52630  
Input D8 = 0  TCNT1 = 55437  ICR = 52630  
Input D8 = 0  TCNT1 = 56724  ICR = 52630  
Input D8 = 0  TCNT1 = 58012  ICR = 52630  
Input D8 = 0  TCNT1 = 59300  ICR = 52630  
Input D8 = 1  TCNT1 = 60588  ICR = 52630  
Input D8 = 1  TCNT1 = 61876  ICR = 52630  
Input D8 = 1  TCNT1 = 63163  ICR = 52630  
Input D8 = 1  TCNT1 = 64451  ICR = 52630  
Input D8 = 1  TCNT1 =   203  ICR = 52630  
Input D8 = 1  TCNT1 =  1458  ICR = 52630  
Input D8 = 1  TCNT1 =  2730  ICR =  2619  D = 15525  T = 993.6000
Input D8 = 0  TCNT1 =  4083  ICR =  2619

Ak chceme merať aj striedu, musíme meranie realizovať s prerušením a v obsluhe prerušenia preklopiť konfiguračný bit, ktorý rozhoduje o prepise TCNT do ICR registra. Je to bit ICES1, ktorý je v TCCR1B.6.

#include <avr/interrupt.h>  

volatile int newTick = 0;   // The variable for interrupt should be declared as a volatile one!
                  
ISR(TIMER1_CAPT_vect)       // Timer 1 Capture Interrupt Service Routine
{
  TCCR1B = ??               // toggle Edge Select bit
  newTick = ICR1;
}; 

main()
{

   DDRB = ??                // Set ICR - Port B, pin0  as INPUT
 TCCR1B = ??                // T1 clk = F_CPU : 1024, falling edge pin ICP1,
 TCCR1A = ??                // T1 in timer mode !! Note: if You omit this, TCNT1 will be only 8-bit !!
  TCNT1 = 0x0000;           // initialize the counter (16-bit! Low+High bytes)
  TIFR1 = ??                // (1<<ICF1);   if a 1 is written to a ICF1 bit
                            //              - the ICF1 bit will be cleared
                      
 TIMSK1 = ??                // Enable ICR interrupt
  sei();                    // Enable ALL interrupts                      

  ....                      // TODO: display measured value somewhere
  
}

Ukážka pre Arduino využíva zabudovaný príkaz PulseIn:

#define SWITCH 8                // select the pin for Switch
unsigned long duration;

void setup()
{
 pinMode(SWITCH, INPUT);        // this pin is an INPUT
 Serial.begin(9600);
 Serial.println("PulsIn test:");
}

void loop()                      // endless loop
{
 duration = pulseIn(SWITCH, HIGH);
 Serial.print(" T1 = ");
 Serial.print(duration,DEC);
 Serial.print(" [us]");

 duration = pulseIn(SWITCH, LOW);
 Serial.print(" T0 = ");
 Serial.print(duration,DEC);
 Serial.println(" [us]");
}