7 Replies Latest reply on Jul 26, 2010 12:47 PM by FredM

    LTspice for Theremin circuits


      LTspice is available free from http://www.linear.com/

      This simulator is superb, and suitable for all designers, from beginners to 'advanced'.. It is well suited to simulation of Theremin circuits.


      The best tutorial I have found to get you started can be downloaded at



      This zip file contains a PowerPoint presentation SWCAD.PPT  and running this teaches you all the basics you need start using LTspice.


      The Full reference manual is here: http://ltspice.linear.com/software/scad3.pdf

      A few good guides:

      http://web.cecs.pdx.edu/~ssuzuki/engr_notes/ltspice/LTSpice_help.pdf (A good tutorial, particularly on setting up simulation types and creating subcircuits.)

      http://pages.suddenlink.net/wa5bdu/ltguide.pdf  (useful tutorial - data on transformers..)

      http://home.mindspring.com/~eeweb/ltspicesubckts.pdf (more advanced sub-circuits)

      http://www.ece.pdx.edu/~prasads/LTSpice%20Sweep%20Tutorial.pdf   (PARAMETER SWEEPING)

      http://denethor.wlu.ca/ltspice/  (Tutorial and lots of good links)


      LTspice is best for Analogue simulations in my opinion - The digital models are a pain.


      For anyone having problems downloading LTspice, I have attached it to this message.. Probably not something I should be doing.. but as I am promoting their software, I hope Linear Technology wont object!

        • Re: LTspice for Theremin circuits

          I went to the Linear Tech site and started to download the LTSpice installer. I was told that my email address is insufficiently sweet smelling. Their list of rejects includes gmail.com, hotmail.com and yahoo.com. OK, I can see their point.


          They allow that they might register you if you write to them, so I copied the page, after replacing my password choice with spaces, and wrote to them. We'll see what comes of it.


          In the mean time, I think I'll see how bad a time MultiSim (the free version from Analog Devices) does on understanding LTSpice files. At least I haven't been rejected by them (yet).

            • Re: LTspice for Theremin circuits

              Hi Ray,

              I have no problems.. doesnt even ask for registration.

              see attached .zip

              • Re: LTspice for Theremin circuits

                I have attached the LTspice "original" to the first posting, just in case my WinZip is incompatable with yours ;-) ..

                Element-14 seems to do ita own zipping on .exe files..


                I have also added the documentation (pdf) in case you cant get that from Linear Technology


                Getting other simultors to run each others files aint worth the effort.. netlists may be compatible, but thats where it ends - symbol formats, schematic formats etc are all different - its easier just to re-draw the schematic than to try to export / import files..


                I mainly use LabCenter Proteus (to me, this is by far the best combined schematic / simulation / PCB package available at any price) Proteus allows simulation of microcontrollers - one can simulate entire MCU/Digital/PLD/Analogue systems, and do hardware and software debugging simultaneously - Almost as good as having a real circuit, ICE, Logic analyser, oscilloscope etc ... Except that complex circuits do not simulate in real time.. so what one might do in 10 minutes on the bench can take a couple of hours on the PC!


                Apart from that - the idea is great :-)  In reality, one usually debugs in stages - and this really works well (for everything except Theremins :-()

                  • Re: LTspice for Theremin circuits



                    Thanks much for the files, which I will resort to if LT doesn't get back to me today (or rejects my plea.) I guess I didn't make myself clear:

                    LT will let anyone  have their simulator and its documentation for free, no problems, but to _register_ you have to have what they are willing to consider a "security sensitive" email.


                    Anyone can get a gmail address just for the asking, and they find it easier to administrate their samples-giveaway program and their software maintenance system by limiting who they will automagically hand out 'yes'es to. In my case, I think I have a quite legitimate claim to their programs, being a working technician and a private inventor who, who can tell, might just invent something everyone wants and would sell millions of LT ICs. Frankly, the majority of IC companies will feed folk like us better than 'legit' engineers, because the legit engineers are too ready to fall into patterns. Last power supply used National parts, all power supplies must use National parts. Us poor bottom-benchers are more likely to say, oooh, I have a sample from LT that might make a good PS for this, let's slot it in and see what it does!"


                    That was one of my real enjoyable bits when I worked for UTRC, in fact: after giving me his canned spiel, the local Newark field sales guy (Newark is the US version of Farnell, at least now) he'd lead me out ot his car, and any databook of sample box that didn't have a destination already chosen for it was mine to take if I wanted. (Even years before that, this same sales guy gave me the whole databook and programming manual set for the Pace microprocessor that National was fronting at the time: it was like the 1802 on stearoids. I didn't buy any, but I did learn a bunch about uP from it, so I was able to buy other stuff from them.


                    If anyone else reading the group is in my position, taking the effort to learn the math and apply it, capable of waving a soldering iron without damaging yourself too badly, and interested in design, call your local Newark (or Farnell?) and see if they're willing to support you. I have my own account with Newark for at home as well as the one I used at Pfizer (which I moved with me to IPG.) When I was going to UCONN for EE (which unfortunately aborted) I was able to buy equipment the bookstore didn't have from Newark at deeply discounted prices!


                    So anyway, if I don't get registered with LT, I'll download the files, but if I do, I'll feel better about being able to keep the software up to date.


                    And I apologize for what has become another OT subthread.


                      • Re: LTspice for Theremin circuits

                        Yes -

                        I have found Farnell to be extremely helpful over many years..

                        They know what we (Designers, Engineers, Technicians etc) need, and they know that supplying high quality samples and data at an early stage in a project (or engineers ;-) development is "planting a seed" - It may be costly - but this cost is more than recovered when the tree starts bearing fruit.


                        Element-14 is, to me, the latest example - it clearly shows that these people understand what we need, and provide it for us!


                        ** End of Farnell Advert ** LOL!

                        • Re: LTspice for Theremin circuits

                          "So anyway, if I don't get registered with LT, I'll download the files, but if I do, I'll feel better about being able to keep the software up to date."


                          You dont need to worry about this.. LTspice has an automatic upgrade facility built into it, and you do not need to be registered to invoke this.


                          In LTspice, click [Tools][Sync] and updates (both executables and updated files) will be automatically downloaded and installed.. It is much more comprehensive than most upgrade utilities.. you can see it checking all the files in its home directory on your drive, and then upgrading ones from LT with newer versions if they exist.


                          Every so often (dont know how long..) if you havent upgraded recently, when you invoke LTspice, it will advise you to check for upgrades..


                          This program is the epitome of software quality, in my opinion... I wish some programs I have paid a lot of money for would work half as well.

                    • Re: LTspice for Theremin circuits
                      Some more advice on simulating..

                      Work with minimum circuit blocks first.. For example, with a Theremin front-end..

                      'Build' ONE oscillator and test it.. usually the oscillators are almost identical.

                      'build' the mixer - but instead of using 'actual' oscillators, use sine generators (these can have their frequency and amplitudes set to whatever you want - specify the amplitude you got from your 'real' oscillator, and set one frequency (variable oscillator) at the frequency of your 'real' oscillator, and the other at say 200Hz higher..

                      You can now test the mixer quickly - the simulation does not need to compute all the signals to make each oscillator run - there is no delay while DC levels stabilize - the simulation will run at least 1000 times faster!

                      When you have tested each block independently, select a time when you wont need to use your PC for severaL HOURS, put all the blocks together, and run the simulation... It is a good idea to do a complete simulation (if possible) once each block has been verified - because you may have missed something... For example, any loading caused by the mixer would not affect signal generators, but may affect 'real' oscillators.. Also (as in the case of the EW simulation) the oscillators may couple to each other via the mixer components (with the EW, coupling is provided through C2 and C6) and this changes the waveshape seen from the mixer (on C23) and can cause the oscillators to pull to the same frequency (giving a DC level, and no difference frequency on C23).

                      When running the full simulation, it is a good idea to set the oscillator free-run frequencies to have about 1kHz difference - unless you particularly want to examine oscillator locking.