Re: voltage to resistance convertor?

"Andrew Howard" <ask.me@xxxxxxxxxxxxx> wrote in message
news:75x7e.11503$5F3.4580@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> "Larry Brasfield" <donotspam_larry_brasfield@xxxxxxxxxxx> wrote in message news:iRw7e.17$6A4.418@xxxxxxxxxxxxxxxxxx
>> "Andrew Howard" <ask.me@xxxxxxxxxxxxx> wrote in message
>> news:SLw7e.11499$5F3.11273@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>>> If I have a source of variable voltage ( a sweep generator for example), is there any way to create a source of varying
>>> resistance in proportion to the voltage?
>>>
>>> About the only way I can think of off the top of my head is a light/LDR combination, but I doubt that would be very efficient
>>> or accurate.
>>>
>>> Anyone have any better ideas? Preferably simpler ones, even if it is slightly less accurate. Or maybe someone knows of a
>>> resistance sweep generator...
....
[MOSFET array cut as unlikely to be suitable.]

>> What input and output range to you need, over
>> what frequency range, with what distortion?
>>
>> Another approach is to use a multiplier IC, hooked
>> up as a divider, with voltage input and current fed
>> back from the output to the input. But again, the
>> required specs are necessary to proceed.
....
> The resistance, I will need between 0 and 2k5.

There will be accuracy and current capacity issues with
the low end of that range. What a designer will need
to know, (at least), is: What currents or voltages will be
applied to the resistance?

> Frequency, between about 0.2Hz and about 20Hz.
>
> Distortion isn't really that important, I'll be using it to control something that isn't all that precise anyway.

That will certainly help.

> The input voltage can be between 0V and 9V. I can probably regulate it to anything within that.

Right now, your requirement appears to be:
1. Accept an input voltage, 'Vx', ranging between 0 V and 9 V,
on one port, consisting of pins VxIn and VxRef.
2. Provide a "resistance", 'Ro', on another port, consisting of
pins RoA and RoB.
3. If current is passed thru Ro, the voltage across it should
be Vx * 2500/9, within some unknown tolerance. There is
no presently known limit on what that current might be.
4. If a voltage is applied across Ro, the current passing thru
it should be 9/(2500 * Vx), within some unknown tolerance.
There is no presently known limit on what that voltage might be.
5. The accuracy implied by items 3 and 4 applies only over the
frequency range 0.2 Hz to 20 Hz. Outside that range, any
voltage or current result is acceptable.
6. The connection, if any, between the Vx port and Ro port, is
unspecified. They might be required to be isolated from each
other for an unbounded voltage difference. Or it may be fine
for either RoA or RoB to be connected to VxRef.

I state the above to clarify what is missing. For any of the
unknown bounds and limits, smaller will be easier and if
it can be unipolar rather than having to be bipolar, the
design may be simplified. Not having to isolate the ports
will greatly simplify the problem.

> 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.

> Thanks again,

You're welcome.

--
--Larry Brasfield
email: donotspam_larry_brasfield@xxxxxxxxxxx
Above views may belong only to me.


.

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