Arduino Quadrature Encoder

Early quadrature encoder development. Not functional – example only

Much of this is from here

volatile long timeA, oldtimeA;
volatile long timeB, oldtimeB;
volatile int LEDstate = LOW;

int tryingToUnderstand = 0;

void A()  //interrupt for channel A
{
 timeA = millis(); // consider overflow and disable interrupts
 LEDstate = !LEDstate;
}

void B()  //interrupt for channel B
{
 timeB = millis(); // consider overflow and disable interrupts
 LEDstate = !LEDstate;
}

void setup ()
{
 pinMode(2, INPUT);    // interupt 0 is on pin 2
 pinMode(3, INPUT);   // interupt 1 is on pin 3
 pinMode(13, OUTPUT);  // heartbeat or debugging

 Serial.begin(9600);

 oldtimeA = timeA = 0;
 oldtimeB = timeB = 0;

 attachInterrupt(0, A, FALLING);  //interupt on falling edge; int 0 is on pin 2
 attachInterrupt(1, B, FALLING);  //interupt on falling edge; int 1 is on pin 3
}

void loop()
{

 // don't do anything unless something has changed
 if ( (timeA - oldtimeA) || (timeB - oldtimeB) )
 {

 // For understanding what's going on
 if (tryingToUnderstand)
 {
 digitalWrite(13, LEDstate);  // update the heartbeat

 Serial.print("timeA old ");
 Serial.print(oldtimeA);
 Serial.print("  new ");
 Serial.print(timeA);

 Serial.print("    timeB old ");
 Serial.print(oldtimeB);
 Serial.print("  new ");
 Serial.println(timeB);
 }

 // Real application
 // What range would we expect to see? According to data sheet there are 200
 // transitions per revolution. Knowing the range of speeds that a visitor
 // might turn the knob we could calculate the range of milliseconds expected
 // between interupts

 if ( (timeA - timeB) > 100 )
 Serial.println("right");
 if ( (timeA - timeB) < -100)
 Serial.println("left");

 // Since something has changed, record this time
 oldtimeA = timeA;
 oldtimeB = timeB;

 }

}

Quadrature decoder that works properly

volatile long timeA, oldtimeA;
volatile long timeB, oldtimeB;
volatile int LEDstate = LOW;

int tryingToUnderstand = 0;

void A()  //interrupt for channel A
{
 timeA = millis(); // consider overflow and disable interrupts
 LEDstate = !LEDstate;
}

void B()  //interrupt for channel B
{
 timeB = millis(); // consider overflow and disable interrupts
 LEDstate = !LEDstate;
}

void setup ()
{
 pinMode(2, INPUT);    // interupt 0 is on pin 2
 pinMode(3, INPUT);   // interupt 1 is on pin 3
 pinMode(13, OUTPUT);  // heartbeat or debugging

 Serial.begin(9600);

 oldtimeA = timeA = 0;
 oldtimeB = timeB = 0;

 attachInterrupt(0, A, FALLING);  //interupt on falling edge; int 0 is on pin 2
 attachInterrupt(1, B, FALLING);  //interupt on falling edge; int 1 is on pin 3
}

void loop()
{

 // don't do anything unless something has changed
 if ( (timeA - oldtimeA) || (timeB - oldtimeB) )
 {

 // For understanding what's going on
 if (tryingToUnderstand)
 {
 digitalWrite(13, LEDstate);  // update the heartbeat

 Serial.print("timeA old ");
 Serial.print(oldtimeA);
 Serial.print("  new ");
 Serial.print(timeA);

 Serial.print("    timeB old ");
 Serial.print(oldtimeB);
 Serial.print("  new ");
 Serial.println(timeB);
 }

 // Real application
 // What range would we expect to see? According to data sheet there are 200
 // transitions per revolution. Knowing the range of speeds that a visitor
 // might turn the knob we could calculate the range of milliseconds expected
 // between interupts

 if ( (timeA - timeB) > 100 )
 Serial.println("right");
 if ( (timeA - timeB) < -100)
 Serial.println("left");

 // Since something has changed, record this time
 oldtimeA = timeA;
 oldtimeB = timeB;

 }

}

And here is the minimal example of interrupts:

volatile long LEDstate;

void ding()
{
 LEDstate = !LEDstate;
}

void setup ()
{
 pinMode(2, INPUT);    // interrupt 0 is on pin 2
 pinMode(13, OUTPUT);  // heartbeat or debugging

 attachInterrupt(0, ding, FALLING);  //interupt on falling edge; int 0 is on pin 2
}

void loop()
{
 delay(10);
 digitalWrite(13, LEDstate);
}