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I'm trying to use a mirror galvo controlled by a mega 2560 to direct a laser. As a first test I want the laser to move along one axis by jumping equal intervals, but I'm having trouble. I'd like to know whether there are any obvious problems in my code (which I suspect may be the case as I'm new to timers and interrupts)?

void setup()
{
  TCCR3B = _BV(CS30); //high freq ~50khz
  pinMode(5, OUTPUT);
}    

void loop() {
 int output1= 5;
 while(output1<255){
  analogWrite(5,output1);
  output1+=40;
  delay(500);
 }
 output1=5;
}

When I run this code the mirror does achieve the full 5 degree range of movement it should. The problem is instead of moving equal intervals the mirror rotates the equivalent of .8 deg over what I suppose are the first two iterations of the while loop, then the mirror jump around 3.5deg of rotation. Then the mirror goes back to rotating by small increments again .75 deg for the last few iterations of the while loop.

I originally tried using my own settings for all timer and PWM settings, that did not work either:

void setup()
{           
   TCCR3A = TCCR3B = 0;
   TCCR3A =  _BV(COM3A1) | _BV(WGM31); //non-inverting
   TCCR3B = _BV(CS30) | _BV(WGM32) | _BV(WGM33); //prescalar=1, fast pwm
   ICR3= 500;
   OCR3A= 6;
   pinMode(5, OUTPUT);
}

void loop() {
  while(OCR3A<500){
    OCR3A+=80;
    delay(500);
  }
  OCR3A=6;
}

Using this second code the mirror rotates by a constant 1 degree and stays put there.

edit: I do have a current gain circuit between the arduino and the mirrors, but I've tested both that circuit and the mirrors with a function generator. Off the function generator they work fine.

user2663116
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  • We need more information on how your mirror galvo is controlled. How does the PWM get translated into steps, is there some driver in between the motor and the arduino? – user2461391 Aug 08 '13 at 12:54
  • First time using stackoverflow so I'm not sure whether I'm supposed to edit in responses, or add them here? So I did both: I do have a current gain circuit between the arduino and the mirrors, but I've tested both that circuit and the mirrors with a function generator. Off the function generator they work fine. – user2663116 Aug 08 '13 at 17:56

0 Answers0