Timer pins for PWM are different depending on the board your using

[photodude]

Timer 1 PWM pins on the Uno are 9 and 10 but on the Mega Timer 1 pins for PWM are 11, and 12.
the PWM frequency change needs to be more robust to handle cases of any timer 1 PWM pin and differences between boards.

For examples on how to do this see:

• https://github.com/fizcris/PWM_frequency_Arduino_change
  and
• https://github.com/abrightwell/arduino-pwm-frequency-library

[photodude]

Code in master branch should now work with uno on either PWM pin for timer 1