Tight loops on Arduino UNO

[colbec]

There's something happening when UNO is looping fast which I should understand more fully.

My goal is to have a Piezo buzzer buzz at a rate dependent on the light level. Stronger light, higher pitch. Here is my proggie which I adapted from the CIRC-06 Piezo experiment from Ardx.org. Note that there is serial output to see what numbers are being delivered from the map and constrain, also there is a 5 second delay to ensure I can reset and upload without difficulty.

Code: [Select]

// Colin Beckingham
// drive a piezo element according to light level
//
int pzPin = 9;
int ldPin = 0;
int lvl = 0;
int duration = 0;
int i = 0;
//
void setup() {
 pinMode(pzPin,OUTPUT);
 Serial.begin(9600);
 delay(5000);
}
//
void loop() {
// read from light sensor (0-900)
lvl = analogRead(ldPin);
lvl = map(lvl,0,900,900,8000);
lvl = constrain(lvl,900,8000);
// output to piezo
Serial.println(lvl);
playTone(lvl);
delay(1000);
}
//
void playTone(int pitch) {
 for (i=0;i<100;i++) {
digitalWrite(pzPin,HIGH);
delayMicroseconds(pitch);
digitalWrite(pzPin,LOW);
delayMicroseconds(pitch);
 }
}

The above code works no problem. The issue is when I reduce the 1000 delay in the loop() to zero. (Note: I found that this was in a practical sense a bad idea since my attempts to upload were stifled by the serial output. The Arduino host machine could not "break into" the attached UNO board. So after I succeeded finally I added the delay.) Anyway, while the board was running with no delay the piezo did not vary in pitch. I was expecting that it would rise and fall as light level changed (as it does correctly with the delay in place) but it just put out a steady pitch, the one it started at.

So, something must be happening that I do not yet see. It may be that the difficulty uploading at zero delay and the invariant buzz are the result of the same phenomenon?

[PaulS]

It may be that the difficulty uploading at zero delay and the invariant buzz are the result of the same phenomenon?

You are not actually calling delay with a value of 0 are you? I hope that you mean "with no delay" rather than "with 0 delay".

[colbec]

No, actually the delay() would simply be commented out.

I think I made my question a bit murky since there are two delays. One is in the setup() to run once at the beginning to allow for maintenance which remains and is important. The second one is in the loop(). Issue arises when the delay in the loop is commented out.

[PaulS]

Issue arises when the delay in the loop is commented out.

Is it still an issue if you comment out the Serial.print() statement, too?