Rotary encoder is giving less PPR reading

Question

I am testing 400 PPR(Pulses Per Revolution) rotary encoder using code.I am rotating it by using the hand. I have connected Phase A and Phase B and also, ground and Vcc properly. The code is giving less than 400 counts in every rotation.eg. sometimes 385,350,360,390. Maximum time the range is in between 350 to 400. The code is given below:

#define PIN1 14
#define PIN2 10

volatile long pos;

volatile uint8_t state;

void pin_isr(void) 
{
    uint8_t p1val = digitalRead(PIN1);

    uint8_t p2val = digitalRead(PIN2);

    uint8_t s = state & 3;

    if (p1val) s |= 4;
    if (p2val) s |= 8;
    state = (s >> 2);

    switch (s) {
        case 1: case 7: case 8: case 14:
            pos++;
            return;
        case 2: case 4: case 11: case 13:
            pos--;
            return;
        case 3: case 12:
            pos += 2;
            return;
        case 6: case 9:
            pos -= 2;
            return;
    }
}
int main(int argc, const char * argv[]) {

    // sets up the wiringPi library
    if (wiringPiSetup() < 0) {
        perror("wiringPiSetup");
        exit(EXIT_FAILURE);
    }   
    pinMode (PIN1,  INPUT) ;
    pinMode (PIN2,  INPUT) ;
    pullUpDnControl(PIN1, PUD_UP);
    pullUpDnControl(PIN2, PUD_UP); 
    if ( wiringPiISR (PIN1, INT_EDGE_BOTH, &pin_isr) < 0 ) {
        perror("wiringPiISR");
        exit(EXIT_FAILURE);
    }

    if ( wiringPiISR (PIN2, INT_EDGE_BOTH, &pin_isr) < 0 ) {
        perror("wiringPiISR");
        exit(EXIT_FAILURE);
    }

    // Show position every second
    while ( 1 ) {
        printf( "%ld\n", pos);
        delay( 10 ); // wait 1 second
    }   
    return 0;
}

I have written similar code for Arduino which perfectly working fine. Every time I am getting exactly 400 counts per rotation. Does anyone know what is the exact problem?

Answer 1

You have not given enough details. The most important factor is the frequency of pulses. Is that 400 pulses an hour, a minute, a second, a millisecond?

I am going to assume the pulses are too frequent and the Linux interrupt system can not keep up.

Try one of the following examples to see if you get the same problem.

C: http://abyz.me.uk/rpi/pigpio/examples.html#C_rotary_encoder_c

C + pigpio daemon: http://abyz.me.uk/rpi/pigpio/examples.html#pdif2_RED

Python + pigpio daemon: http://abyz.me.uk/rpi/pigpio/examples.html#Python_rotary_encoder_py