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external Clock on Timer1

use Tiemr1 to count pulses, set external clock, access 16-Bit Register TCNT1

/**************************************************************************************************
*
*   photoInterrupter_countWithTimer1_00
*
*   Version:      00 - Mai 2010
*   Author:       Tom Pawlofsky www.caad.arch.ethz.ch tom-DOT-pawlofsky-AT-arch-DOT-ethz-DOT-ch
*
*   Desc:         count the events on a photointerrupter / lightbarrier within the Counter
*
***************************************************************************************************/

// using a Sharp GP1A53HR
// the Infrared-Led is connected
// no 1 Anode via a 470 Ohm to 5V -> less then 10 mA
// no 2 Cathode to Gnd
// the Recievers Pins are connect
// no 3 Vcc to Vcc 5V
// no 4 Vo  to Digital Input Pin of MicroController
// no 5 GND to Ground Gnd
//
// Note: this Photointerrupter has a Schmitt Trigger as Output
// this reduces the sensitivity for noise and will always give back LOW or HIGH
//


// this methode of counting offers BEST performance and HIGHEST SENSITIVITY
//
// make sure that you have no noise at input-Pin - you have to filter noise via hardware/electronics eg. a Schmitt Trigger
// make sure you have a proper powersupply for your Microcontroller ( best a battery )
// make sure you have no disturbing electronics near to your setup
// make sure your wires are proper connected

// Timer0 and Timer2 can only count from 0 to 255 - 8 Bit
// Timer1 can count to 65535 - 16 Bit
// Timer1 is also used to generate the PWM on the OC1A and OC1B - Pins - should be Pin 9 and 10 (ATM168)
// if you use this method of counting you can not us analogWrite at those Pins, digitalWrite still works fine


int pinLB = 5; // LIghtBarrier, Photointerrupter -> you must use ATM168-Pin-T1 see p108 of ATM168 datasheet



void setup(){
        // start serial communication
        Serial.begin(9600);

        // define pins
        timer1SetExternalClock();


}



void loop(){


        // feedback of counter
        Serial.print("counter ");
        Serial.println(readTCNT1(),DEC);

        //
        delay(300);
}


//
void timer1SetExternalClock(void)
{
        // Timer 1 16 Bit, 0 - 65535
        //__________________________________TIMER1_for_Encoder_________________________________
        //the entire Timer-Register is rewritten, destroying all Arduino Timer-settings
        // that a done in the init() function - see wiring.c
        // http://code.google.com/p/arduino/source/browse/trunk/hardware/arduino/cores/arduino/wiring.c
        // no pwm / no analogWrite on Pin 9, 10
        // Timer1 Setting - Reset - this will also stop the timer
        TCCR1A = 0;
        TCCR1B = 0;
        TCCR1C = 0;
        // clear Timer
        writeTCNT1(0);//
        // Mode of Operation Atmega168 datasheet p131
        // OR
        // fast PWM MAX = OCR1A, bad update of OCR1A
        // TCCR1B |= (1<<WGM13) | (1<<WGM12);
        // TCCR1A |= (1<<WGM11) | (1<<WGM10);
        // OR
        // fast CTC MAX = OCR1A, immediate update of OCR1A
        //TCCR1B |= (0<<WGM13) | (1<<WGM12);
        //TCCR1A |= (0<<WGM11) | (0<<WGM10);
        // OR
        // normal Mode, immediate update of OCR1A
        TCCR1B |= (0<<WGM13) | (0<<WGM12);
        TCCR1A |= (0<<WGM11) | (0<<WGM10);

        //Timer1 Overflow Interrupt Disable
        TIMSK1 = 0;

        pinMode(pinLB,INPUT); // pinLB must be 5

        // set Prescaler Atmega168 datasheet p132 - this will also start the timer, do this at end of all setup
        //
        // external clock on pin5 falling edge
        TCCR1B |= (1<<CS12) | (1<<CS11) | (0<<CS10);
        // OR
        // external clock on pin5 rising edge
        // TCCR1B |= (1<<CS12) | (1<<CS11) | (1<<CS10);
        // this will also start the timer
}

// read and write 16Bit-Counter as shown in ATM168 - datasheet page 112

void writeTCNT1(unsigned int num) {
        unsigned char sreg;
        unsigned int i;
        if (num >= 0) {
                /* Save global interrupt flag */
                sreg = SREG;

                /* Disable interrupts */
                cli();
                // set new value
                TCNT1 = num;
                /* Restore global interrupt flag */
                SREG = sreg;
        }
}


unsigned int readTCNT1( void )
{
        unsigned char sreg;
        unsigned int i;
        /* Save global interrupt flag */
        sreg = SREG;
        /* Disable interrupts */
        cli();
        /* Read TCNT1 into i */
        i = TCNT1;
        /* Restore global interrupt flag */
        SREG = sreg;
        return i;
}

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Article by Tom Pawlofsky Mai 2010

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