Hi,

I am using the Arduino Uno to generate different frequency square waves to modulate an LED. I am using the toggle on compare match mode of the 16MHz clock on the ATMega 328 to do this. The datasheet for the ATMega 328 has a nice formula for calculating the OCRnA register value needed to generate the desired output frequency. When I calculate the register value and hardcode the OCR1A register, for 500Hz the register value is 1999, it outputs the correct frequency. What I would like to do is just to have a int variable frequency where I can simply enter 500 and then it will calculate the OCR1A value but when I try to implement this the frequency that is outputted is random. I can't seem to figure out why this is. Here is a little bit of my code:

For 500Hz

//This works

OCR1A =1999 ;

//This doesn't work

int freq = 500;

int eq = ((16*10^6)/(2*8*500))-1; //This is the formula from the datasheet and

// what I used to get 1999 above

OCR1A = eq;

Can anyone see what I am doing wrong? Thanks in advance.