Path: csiph.com!eternal-september.org!feeder.eternal-september.org!nntp.eternal-september.org!.POSTED!not-for-mail From: Christopher Howard Newsgroups: sci.electronics.design Subject: Re: one potentiometer dividing multiple signals Date: Mon, 23 Mar 2026 09:09:35 -0800 Organization: A noiseless patient Spider Lines: 53 Message-ID: <87ikam1nhs.fsf@librehacker.com> References: <87ldfr6bqo.fsf@librehacker.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Injection-Date: Mon, 23 Mar 2026 17:09:37 +0000 (UTC) Injection-Info: dont-email.me; posting-host="1c7b2805601a8e52cd5fa8fd8025e2e4"; logging-data="339469"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX19O2E+7QmBKeOy1TXz3uq031HHe0qNBFuY=" User-Agent: Gnus/5.13 (Gnus v5.13) Cancel-Lock: sha1:/+CzZssPzWmU7U+M7QSJFbiAH0U= sha1:rX38bhLSzDJ96ryNo24VzFrE8zs= Xref: csiph.com sci.electronics.design:742154 > If you use a real pot in an analog computer, how do you set the > coefficients? > THAT analog computer has a COEFF mode which activates a Potset signal line which disconnects the pot input and activates some measurement circuitry, which in turn shows the setting of the pot as a value between [-1,1]. If that is not available, another approach is to disconnect the input and output lines, then connect the input to +1 MU input, and connect output to meter. > > Why not use Spice? I know people who are afraid to use Spice. LT Spice > is free and I teach people to use it in 10 minutes. > One problem is that LT Spice is not available as a package for my Guix Gnu/Linux computer. Presumably this is because it is not available under a free software license (FSF definition) and also was designed for Windows. I have also little desire to run anything on a desktop simulator, as my goal is to learn and experiment building simulations/models on my actual analog computer. THAT is a very nice analog computer, though I found that the latest model I wanted to experiment with requires a few more pots and multipliers than I currently have. I built my own expansion module, adding an extra multiplier, and am pondering building some more pots and comparator modules. THAT can be daisy chained with another THAT computer, which is cool, but buying another THAT is about 600 USD. A year or so ago, I did look a bit into getting some other spice-type programs that would run on my Guix system. KiCAD has an interface compatible with ngspice, but I found that the work of using it was a lot more bother than it was worth to me. I tried also programming directly in ngspice but as you can imagine that wasn't very practical. There is an interesting program called Xcos which I wanted to play around with, but I was having a lot of trouble getting the Javascript to build on my system — required for the gfx interface. I suppose I might pursue that further at some point, but I do not feel much motivation at present. There is another program called pydda, for setting up numerical simulation of differential equation systems, which I played around with. Unfortunately, however, it is not maintained anymore and need some more features. I'm not much interested in digital programming these days and even less so in python. Been casually looking into some other things on occasion, like Julia's differential equation libraries. -- Christopher Howard