Quote Originally Posted by malc-c View Post
However, the amount of rotation of the pot is quite small before the loco is up to a medium speed. I've tried changing the pot for 100K, 22K and even 2k, and I've played about with different values for R1, R2 and R3 and it still makes no difference.
Are you using a linear pot or a 'log' ('audio') pot? I've been tripped up by those before, thought I had a linear type, ended up being a log type.

Is there a way to "scale" or range the ADC so that the PWM performs is less proportional, and more log like in action
Maybe use PBP's built in SIN function. It won't be LOG-like, but if you use the first 90 degrees...upside down (if that makes any sense) and a bit of programming, at least it won't be a linear function and should be a bit smoother at the low end.

Also, what would be the best way to protect the PIC from interfearence, placing 0.1uf caps between inputs and gnd or simply take all unsused pins to gnd ?
Pulling all unused inputs to either Vdd or Vdd is never a bad idea.
Putting .1uf across all the inputs might 'slow down' the inputs, you might miss a pulse for something here and there. Maybe you need more than .1uf across Vdd & Vss on your PIC, 'cause the .1uf tends to only decouple one frequency range, generally the higher ones. Maybe you need to add a big 'ol 10uf or something in parallel with that .1uf, to help get some of the lower frequencies. And maybe make sure you've got good quality cap's doing that job, low ESR types.