Quote Originally Posted by cncmachineguy View Post
Hi Hank, just stabbing at this, you second set of numbers is not really all over, every other one is close to the last. I am guessing here maybe timer is overflowing with the lower freq?
hi bert,

Very plausible/good idea, but alas, it's not down to Timer1 overflowing (I worked out that with a 16 bit timer @16Mhz oscillator I can go down to about 58hz before worrying about overflows), for example if i take the frequency even lower than 800hz, it goes fairly stable again, here's 500Hz...

3120
3218
3212
3208
3202
3198
3194
3184
3182
3179
3173
3168
3163
3154
3151
3150