Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail From: John R Walliker Newsgroups: sci.electronics.design Subject: Re: Designs of voltage/current controlled resistance Date: Wed, 21 May 2025 20:23:16 +0100 Organization: A noiseless patient Spider Lines: 61 Message-ID: <100l974$2nno5$1@dont-email.me> References: <100kurj$2i6q$1@nnrp.usenet.blueworldhosting.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Injection-Date: Wed, 21 May 2025 21:23:17 +0200 (CEST) Injection-Info: dont-email.me; posting-host="de92aa546e075958aeeae37ffc398526"; logging-data="2875141"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1/izwUoJK19o/jLvLCaX664g+vyPX5EV9U=" User-Agent: Mozilla Thunderbird Cancel-Lock: sha1:09KVu2qV9jhElAONEcPdEQFFFTE= In-Reply-To: <100kurj$2i6q$1@nnrp.usenet.blueworldhosting.com> Content-Language: en-US Bytes: 3391 On 21/05/2025 17:26, Edward Rawde wrote: > "RodionGork" 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 > >