Hi all:
You've probably had this question a lot, so I'm sorry if repeating. I am trying to use pin 2 to read pulse width from an RC receiver on a quadcopter, and set the lights accordingly. The ISR should read the system clock in microseconds when the pulse starts and when it completes followed by simple subtraction to get pulsewidth in microseconds. The pulses range from perhaps 900 to 2100 microseconds, with approximately a 22 millisecond delay between them. The logic is pulse high. All of the light patterns work when tested in the code (by setting the initial value of the pulseWidth variable to a range accomodated by the logic (900-2100 microseconds). The interrupt does not trigger, however, when driven with a pulse generator. The code is attached here:
#define PULSE_PIN 2
#define LED0 10 // left front led
#define LED1 11 // right front led
#define LED2 12 // right rear led
#define LED3 13 // left rear led
//Times are in ms
#define STROBE_ON 20
#define STROBE_OFF 800
#define STROBE_DLY 100
#define ALT_PD 350
#define FRONT_BACK 0
#define SIDE_SIDE 1
#define DIAGONAL 3
#define CW 1
#define CCW 0
#define CYCLES 5
//tell the compiler that these WILL change
volatile int lights[4] = { LED0, LED1, LED2, LED3 };
volatile long pulseStart = 0;
volatile long pulseWidth = 1700;
//Do setup routine...define pin functions
void setup(){
pinMode ( PULSE_PIN, INPUT );
pinMode ( LED0, OUTPUT );
pinMode ( LED1, OUTPUT );
pinMode ( LED2, OUTPUT );
pinMode ( LED3, OUTPUT );
attachInterrupt( (PULSE_PIN - 2),ISRpwTrigger, CHANGE );
}
void ISRpwTrigger() {
if( digitalRead( PULSE_PIN == HIGH ) )
pulseStart = micros();
else
pulseWidth = micros() - pulseStart;
}
//light all of the leds simultaneously
void allLight(){
digitalWrite ( LED0, HIGH );
digitalWrite ( LED1, HIGH );
digitalWrite ( LED2, HIGH );
digitalWrite ( LED3, HIGH );
}
//turn all lights off
void allDark(){
digitalWrite ( LED0, LOW );
digitalWrite ( LED1, LOW );
digitalWrite ( LED2, LOW );
digitalWrite ( LED3, LOW );
}
void allBlink(){
allLight();
delay ( STROBE_ON );
allDark();
delay ( STROBE_OFF );
}
void wingtipStrobe( int count ) {
for ( int counter = 0; counter < count; counter++ ) {
allLight();
delay ( STROBE_ON );
allDark();
delay ( STROBE_DLY );
}
delay ( STROBE_OFF );
}
//alternate blinks--pass in pin order and delay ms
void altBlink ( int mode, int dly ) {
//remember...LED0 is always in the first position
// we are going to always use the pattern [1] and [2],then [3] and [4];
lights[0] = LED0;
switch( mode ) {
case FRONT_BACK:
lights[1] = LED1;
lights[2] = LED2;
lights[3] = LED3;
break;
case SIDE_SIDE:
lights[1] = LED3;
lights[2] = LED1;
lights[3] = LED2;
break;
case DIAGONAL:
lights[1] = LED2;
lights[2] = LED1;
lights[3] = LED3;
break;
default:
allLight();
return;
}
digitalWrite ( lights[0], HIGH );
digitalWrite ( lights[1], HIGH );
digitalWrite ( lights[2], LOW );
digitalWrite ( lights[3], LOW );
delay ( dly );
digitalWrite ( lights[0], LOW );
digitalWrite ( lights[1], LOW );
digitalWrite ( lights[2], HIGH );
digitalWrite ( lights[3], HIGH );
delay ( dly );
allDark();
}
void ringBlink( int dir, int dly ) {
int index;
if ( dir != CCW ){
lights[0] = LED0;
lights[1] = LED1;
lights[2] = LED2;
lights[3] = LED3;
} else {
lights[0] = LED3;
lights[1] = LED2;
lights[2] = LED1;
lights[3] = LED0;
}
for (index = 0; index < 4; index++){
digitalWrite ( lights[index], HIGH );
digitalWrite ( lights[(index +1)%4], LOW );
digitalWrite ( lights[(index +2)%4], LOW );
digitalWrite ( lights[(index +3)%4], LOW );
delay(dly);
}
allDark();
}
//loop will run forever, but the system is interrupt driven
void loop(){
if ( pulseWidth > 900 ) {
if ( pulseWidth < 1100 ) allDark();
else if ( pulseWidth < 1250 ) wingtipStrobe( 2 );
else if ( pulseWidth < 1400 ) altBlink( FRONT_BACK, ALT_PD );
else if ( pulseWidth < 1550 ) altBlink( SIDE_SIDE, ALT_PD );
else if ( pulseWidth < 1700 ) altBlink( DIAGONAL, ALT_PD );
else if ( pulseWidth < 1850 ) ringBlink( CW, 100 );
} else allLight();
}
Pin 2 is held low by a 10k resistor to ground with the pulse being delivered at the pin 2 side of the resistor ;). I have also tried a 330 ohm resistor with the same results.
I have run similar programs on a UNO development board and it accurately reports the pulsewidth to an LED monitor.
What am I doing wrong 
