Martini ... you appear to be an expert on the Zero and PWM so maybe there is a simpler method to accomplish what I am trying to do. I had posted the comments below on another section of the forum and was redirected here, and had tried exactly the same thing (to change the PWM frrequency on the Zero (pin 9) that shiram has listed above based on something I found on another post:
Pins 9 and 10: controlled by timer 1 in phase-correct PWM mode (cycle length = 510)
Setting Divisor Frequency
0x01 1 31372.55
0x02 8 3921.16
0x03 64 490.20 <--DEFAULT
0x04 256 122.55
0x05 1024 30.64
TCCR1B = (TCCR1B & 0b11111000) | ;
So I understood (wrongly, apparently) that changing TCCR1B as above would do the trick. But this line of code doesn't compile as the compiler can't find a declaration of TCCR1B. All I am trying to do is change the PWM frequency from the default of near 190 KHz (187 KHz is a number I've seen posted elsewhere) down to 490 Hz or 123 Hz (or similar ... somewhere in the low 100s).
Is there a simple way to do this, or do I need to follow a much more extensive process (which I think you have outlined above but I am not too clear on all of those details). I did find a library (PWM.h) what was supposed to do this for the Zero, but that also doesn't compile or recognize any of the library functions. I would have thought changing a PWM frequency would be relatively easy for an Arduino, but maybe the Zero is a different animal. 187 KHz is just too high for my application. Thanks for any help.