Re: voltage to resistance convertor?

Andrew Howard wrote:
>>
>>> In case you are wondering, it is for a Guitar FX pedal I am
>>> semi-designing.
>>
>> What sort of circuit is going to use the synthesized
>> resistance? Can it accept a voltage or current instead?
>> There may be an easier way to solve the real problem
>> than synthesizing a resistance.
>
>
> This is the circuit that needs the variable resistance. It is the
> basis for a simple phaser. Apparently it works by using the fact that
> the emiiter is 180 degrees out of phase with the collector (or
> something). The varying resistance has been labelled R1.
> VCC
> + (9V)
> |
> |-----'
> .-. .-.
> 47K| | | |2K2
> | | | |
> '-' '-' 1uF
> | | +[/
> 1uF | '----[|------'
> \] | |/ [\ | |
> IN o------|]---o---| BC548 | | 1uF
> /]+ | |> .-. | \]
> | .----' | |<-----|]----o OUT
> o | | | | |2K5 /]+
> | .-. .-. | '-'R1
> === 22K| | | | | | o
> GND | | | |2K2'---' |
> '-' '-' ===
> |-----' GND
> |
> ===
> GND
>
>

If you want to take digital potentiometer for this task, it should be
possible, but it will require a SPI or similar control signal, not a voltage
input. If you modify the circuit, you might come to a solution with a
multiplyer, but this is not a trivial case either.
You can use the LDR/LED approach, but the lowest resistance will not be 0,
but maybe 400 to 1k, so you get less range into the clean sound, where the
circuit acts merely as a follower. It can be tried out easily, there are
even combinations in a 8DIP readily available, I do not remember the part
numbers, but google should help.
Some manufacturers make motor pots, I saw some surplus ones go for only 6
bucks, but only 10k, not 2k5. (k is not in capital letters, BTW).
--
ciao Ban
Bordighera, Italy


.

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