PWM I am not able to fine tune it

Using Arduino Programming Questions
#1

Here is my code, it works, I can get a frequncy output that is stable. However I can not tune the frequency to my precise value. I have tried changing the analogwrite function from 128 to 255 with no change.
Can any body advise if this can be done.

void setup()
{
TCCR1B = TCCR1B & 0b11111000 | 0x01; //0-7 for the last number

pinMode(9, OUTPUT); // enable the PWM output (you now have a PWM signal on digital pin 10)

}

void loop()
{
analogWrite(9,128); // set the PWM to 50% duty cycle

}

#2

It appears you’ve seen this playground page

http://www.arduino.cc/playground/Main/TimerPWMCheatsheet

as you have this in your code, with replaced with 0x01
TCCR1B = TCCR1B & 0b11111000 | ;

Your frequency choices are limited as shown - the 128 in (9,128) only changes the width of the pulse that occurs at the frequency selected.

Pins 9 and 10: controlled by timer 1
Setting Divisor Frequency
0x01 1 31250
0x02 8 3906.25
0x03 64 488.28125
0x04 256 122.0703125
0x05 1024 30.517578125

#3

Yep your right, I got that page info pointed to me from another post.

I am curious though about why doesn't the change in the width of the pulse change the frequency. Or does it flip the off time with the width of the on time.

#4

Because the frequency is the reciprocal of the high time plus the low time of a pulse. All you are doing is altering the ratio of each but the total remains the same.

#5