--- In
motm@yahoogroups.com, The Old Crow <oldcrow@o...> wrote:
>
> I like this. Of course, you're adding cost to the product with
> more hardware. The large initial frequency control ideally should
> be a 10-turn type, but I don't think they make those for PCB-mount.
I seem to remember this being discussed - one camp liked the idea of
multi-turn pots because it gives you more resolution, the other camp
liked single turn because it allowed relatively easy manual sweep over
a wide range - and felt the combination of coarse and fine knobs will
solve the problem of resolution.
Because the local oscillator is microprocessor generated, I think the
way to do a multi-turn is to use a high resolution optical encoder.
(128 pulses per revolution or maybe more.) This way, you aren't
limited to the resolution of the AD converter that is sampling the
pots. And you can probably find a board mounted optical encoder - in
fact, I know you can :)
The disadvantage of an encoder is there are no end stops but I think
you could come up with a workaround. Say, a couple of LEDs that
indicate when you are at either extreme of the frequency range.
seth