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From: John R Walliker <jrwalliker@gmail.com>
Newsgroups: sci.electronics.design
Subject: Re: Designs of voltage/current controlled resistance
Date: Wed, 21 May 2025 20:23:16 +0100
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On 21/05/2025 17:26, Edward Rawde wrote:
> "RodionGork" <rodiongork@github.com> wrote in message news:d469c760bbcd14a1f148c0e1b29653f7@www.novabbs.com...
>> Hi Friends!
>>
>> What approaches exist of creating voltage or current-controlled
>> resistance?
> 
> Usually opto devices or FETs.
> It has been recently demonstrated here that there are other approaches but it depends on what you're trying to achieve.

To be more specific, have a look at the H11F1 which is an LED
coupled with a bidirectional light sensitive FET.  This has been
around for many decades but is still available.
John

> 
>>
>> There is no some specific schematic in which I want it to be plugged in,
>> but I'm designing a few gadgets related to electronic musical
>> instruments - and sometimes I want such resistance for volume control
>> while at other times to be used in certain frequency generator to
>> control the frequency itself.
>>
>> I vaguely remember there is JFET but care is needed to fit signal into
>> its small-voltage "ohmic" region and provide suitable bias to the gate.
>>
>> Also at least for some schematics opto-couple with resistor in the
>> output part seems viable (though I'm not sure about linearity - on the
>> other hands linearity is not often needed).
>>
>> Next there are motor-driven potentiometers but in my context it looks
>> ridiculous.
>>
>> Also I vaguely remember tube triode has curious voltage-current
>> characteristic which probably means it could be utilized in a way
>> similar to JFET (though it is a bit exotic).
>>
>> And then there are complex and composite devices, digital resistors etc,
>> but I prefer to work out some more "plain" solutions as they are in part
>> for educational purposes (e.g. to be constructed by school pupils).
> 
> If it's for school students I'd have them play with one of these and a variable light source in a closed box.
> 
> https://www.google.com/search?q=ORP12&udm=2
> 
>>
>> May I be missing some fine schematic with a handful BJT or something
>> like this?
> 
> Depends on exactly what you want to achieve.
> 
>>
>> thank you in advance,
>> sincerely yours,
>> Rodion
>>
>> -- 
>> to email me substitute github with gmail please
> 
>