One way I have thought about (but have not tried yet) is to use a=20
mechanical encoder.
Step by 1s.  If you see 10 steps in the same direction, start stepping=20
by 10s.
If you see 10 steps of 10 in the same direction, start stepping by 100s.
If you see 10 steps of 100 in the same direction, start stepping by 1000s.
If you see a step in the opposite direction, go back to stepping by 1s.
I don't know if this would be more of a PITA than it's worth.
An alternative would be to measure the time between encoder pulses, and=20
take bigger steps for quicker pulses.

Kerry


On 7/18/2014 8:17 AM, David C Brown wrote:
> I am building a simple pulse generator using an LTC6903 "synthesiser chip=
"
> and a few TTL chips.  The range will be from about 0.1Hz to 68MHz and the
> frequency is set, geometrically, by a 15 bit control word.  I  will be
> using a PIC16F87 to control the synthesiser and drive a display.
>
> My problem is how to set the frequency by hand  using the minimum panel
> hardware.   I need control at the finest level, stepping the control
> register by one but also need to be able to make large frequency shifts
> quickly, perhaps stepping the register by 2^10
>
> I have studied this for some time and come up with several solutions, non
> of them entirely satisfactory, but I would appreciate, in the first
> instance, suggestions which are not influenced by my thinking.

--=20
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