Frequency Generator

Other Hardware 3rd Party Boards
1

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 = ((1610^6)/(28*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.

2 
int eq = ((16*10^6)/(2*8*500))-1;

10^6 is one million which won't fit in a 16-bit integer. You would be better off working out the constants yourself and using long integers.

[EDIT] Tested, it works [/EDIT]

int eq = 1000000L/freq-1;

Pete

3

int yields a range of -32,768 to 32,767. You might want to consider unsigned long.

You can also simplify the math formula that you gave.

int eq = ((16*10^6)/(2*8*500))-1;
 int eq = ((16*10^6)/(16 * 500))-1;
 int eq = ((1 * 10^6 / 500))-1;