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Experiences of the CT SoundProg Device

YouChoos Resouces

This page is intended to share my own experiences and thoughts on the CT Elektronik PC Programmer interface ('SoundProg') and associated software in relation to programming the SL51-4 sound+motor decoder (also applies to the SL75, SL76, SL82 and GE75 decoders).

What is the CT Programmer?

Put simply, the CT Programmer is a device which you can attach between your PC and a CT decoder in order to load your sounds onto that decoder. You can see a picture of it below, in the form of an open circuit - I've put mine inside an old hard disk power supply case as I prefer not to have exposed electronics sitting on my desk.

CT Programmer PC Interface

CT Programmer

Here I will talk specifically about my experiences in programming the SL51-4 decoder using the CT Programmer, but the information is pretty much identical for the SL75/SL76 (small versions of SL51-4), the GE75 (sound-only version of SL75), and the SL82 (large scale version), all of which are 'revision 4' CT decoders. The revision number of the decoder is very important here, as I know through painful (not to mention expensive) experience that the same setup and software does not work with older revisions.

The Components

Let us first list out the various components used in this process:

  • SL51-4 (or SL75/SL76/SL82/GE75) decoder - this may be installed in a loco already (as I normally do - leaving the programming until the physical install is complete), or may be done right up-front, which has the benefit of testing the decoder very early on for potential faults (luckily uncommon these days).
  • Speaker - the CT Programmer documentation is a little confusing on this subject, but I have found that you DO need a speaker attached to the decoder in order for the programming to work successfully. During the programming you also get a series of 'beeps' from the speaker which confirm that the download of data to the decoder is indeed working ok. More on that later.
  • CT Programmer - this is a small Serial device presented on an exposed circuit board, readily identifiable by a huge capacitor on the top! I'm not sure why CT don't put it in a box. Still, it works, and is functional so I guess I should stop complaining and get on with it!
  • Serial cable - sounds obvious, I know, but this little item caused me the biggest problems of all when originally trying to get the programmer to work. Again, the documentation from CT is incomplete and inaccurate. I could not get a simple serial cable to work at all. So, I tried a serial-to-USB cable (a cheap one from eBay), and that did not work either. Finally I talked to Alan, from Etched Pixels, who had apparently got this working himself and found out from him exactly what cable he had used, and so I got the same model: a Belkin F5U103. Basically it needs to be a cable which has the flow control line properly implemented, and any cable that uses the Prolific 2303 chipset should work just fine.
  • Power supply - again, this isn't obvious as to what PSU/adapter to use - the documentation is somewhat lacking, and there is a general concern by various people that the programmer is very fussy, and it depends upon the type of decoder being programmed too. Anyway, I didn't find any of these things an issue - a simple 15V/500mA DC power adapter works absolutely fine (you can get one for around £10... mine came from DCC Supplies). Perhaps the concerns were with an old version of the programmer, or older decoders.
  • PC - theoretically any PC will do, as long as it can take the cable you've used. I have used it with Windows XP, Win 7 and Win 8.1 successfully, but the software is purely DOS-based, which means it 'should' work with any version of Windows, as long as you can find the Command Prompt!
  • Software - another very tricky area, bady documented. Each decoder and revision appears to need a different level of the low-level software, and if you use the wrong version it has the potential to fry the decoder! During a trip to DCC Supplies we programmed an SL51-2 with the SL51-4 software, and this just ended in a flash of fire and a puff of smoke once we placed the loco on the track. There are 3 elements to the software: something called FILLFLASH; a Windows front-end called SoundProg; and a firmware updating program called UPDATEFL. I'll talk about each of these shortly. Note that YouChoos has developed its own software for creating sound projects for CT sound decoders now, which you can look at here.
  • Data - obviously if you want to program a decoder, then you need some data to put onto it! This comprises 3 basic parts: a list of CV settings; a definition of what sounds to load; the sound files themselves. This is often referred to as a Sound Project, although I tend to call it a Sound-Set because of some differences in the way I put the files together. Please refer to the guide on how to put a Sound-Set together for more information.

Software Elements

As mentioned above, there are essentially 3 software programs available from CT which can be used for the programming of decoders. If you have experienced the equivalent LokSound or Zimo software, then you'll probably be appalled at the CT software, as it is incredibly basic, difficult to use and some of it cannot even be installed on non-Austrian/German PCs!

It is worth appreciating that I myself am a software engineer by profession, so I don't mind the low-level stuff too much, but CT's software is certainly not designed for your average Joe! Luckily you can use YouChoos' own software , which takes most of the pain out of it!

The software is theoretically downloadable from the CT web site (, if you can find it, but you'll need to read German, or get Google to translate it for you. I believe that what is there as I write is all applicable for revision '-4' decoders, but I wouldn't like to guarantee that of course! I'll try to remember to add in details of the exact version of each program below so that you can cross-verify if you try to use a newer or older version. So, let's take a look at the software:

Beware though that CT tend to forget to update their website with the latest software, so ask the question directly if you want to be sure to be up to date.

  • FILLFLASH - this is a low-level program which communicates directly with the CT Programmer, sending it the necessary signals to load the requested CV values and sounds into the decoder. There isn't much to it - it takes 3 parameters from a DOS Command Prompt: name of your CV list file; PC's COM Port where the Programmer is attached; name of your sound-set definition file. When it runs it blurbs out lots of text telling you what it is doing, showing some of the data being processed. It is not at all user-friendly, but at least you can get some idea that something is happening! FILLFLASH is the tool that I use, and nothing else in fact. I believe that older versions of FILLFLASH had a slightly different name - something like FILLFLSH - but that isn't too relevant now. FillFlash V7 is the latest version that I am aware of and works with all rev4 CT sound decoders, as long as they have at least version 123 of the firmware.
  • SoundProg - this is CT's attempt at a nice GUI/Windows interface where you can build your CV lists and define your sound-sets - choosing which sound files should be used for which effect. You can save your work as a Sound Project, which is the term generally used. I deliberately don't call what I do Projects because I don't bother with SoundProg - I just execute FILLFLASH directly with the names of the CV and Sound definition files. I had great difficulty getting SoundProg to install on my PC at all - the installer just kept complaining about runtime components. Various web sites indicated that I needed to temporarily set my PC to German/Austrian settings, do the install, then switch back to English. However, despite trying all that, I never got the installer to complete successfully. However, even with an apparently broken install, it was possible to run the program, which is all in German, and I could never get it to talk to the CT Programmer anyway, so eventually gave up and settled for using FILLFLASH directly instead. Apparently underneath, SoundProg calls FILLFLASH anyway, so technically you are not changing anything - just getting a GUI interface to configure things. In fact, I've now written my own YouChoos software with GUI interface to do all this anyway, which you can take a look at here.
  • UPDATEFL - this little program is another low-level thing which is used for refreshing the FIRMWARE on the decoder. The FIRMWARE is the software on the decoder itself, stored on FLASH memory, so if CT releases an update which gives you fixes or enhancements then it is theoretically possible to update the FIRMWARE and start using those updates, rather than having to replace the whole decoder, or send it back to CT. A neat feature in theory.

Dispelling Myths

There are various myths surrounding the CT software and programming setup, voiced on certain web sites and forums, and it is worth squashing a few right now...

  • Software must be on C: drive - certainly not true of FILLFLASH, which works from any drive. I cannot say for sure about SoundProg, as I only ever put it on C, and wouldn't touch it with a bargepole anyway.
  • Software and data files must use 8.3 format - by this I mean 8 characters for the name and 3 characters for the file extension e.g. "HELLO.TXT" has a name of "HELLO" and an extension of "TXT". This restriction does not appear to be true either - I have had no problems using files in long-named subdirectories, where the names are much longer than 8 characters, and also in directories which contain spaces in their name. However, I suspect this is simply making use of Windows' current directory which means it looks for the files in a location relative to where you run FILLFLASH. I run FILLFLASH from the SAME directory as where all the associated files are held, so that might be why it works for me.
  • You must disconnect the speaker from the decoder during programming - untrue! In fact I've found exactly the opposite - you need to have the speaker connected or the programming doesn't actually work at all. It is also useful to have the speaker connected as it gives you some positive feedback (beeps) that the process is actually working.
  • You can read data OFF the decoder using the CT Programmer - no, sorry, you cannot. It is a nice thought, but unfortunately the Programmer is an entirely one-way device. In fact, the Programmer is so dumb that it does not even know if the decoder is attached - it just blindly sends data through its outputs and begins to pray! The only feedback it gets is that it can detect a short circuit.

Let's See It Work Then!

Perhaps this is beginning to sound a bit negative, and yes, I have many reservations about the programming side of CT decoders, but what we need to concentrate on (having solved the programming issues) is what the results are like... and it is worth the effort...

Enough chat then - if you want to see this in action, or read more detail, then please take a look at the YouChoos software developed for this purpose. Full documentation is provided online for you to read too.

Experiences & Commentaries

YouChoos Resouces

HINT: For document links below, either open them directly in your web browser by clicking the links, or right-click and save target instead...

YouChoos commentary on various decoders    
YouChoos Products

Build your own sounds for CT decoders

YouChoos no longer supplies CT products, but if you are interested in obtaining a license for the YouChoos/CT SoundProg software, this is still available, costing £25 for a single PC license. Note that no further maintenance is planned.

The software was developed by YouChoos and runs on a PC enabling you to build, manage and load your own sound projects into CT sound decoders!

Build your own sounds for CT decoders Costs only £125

Required parts:

  • CT SoundProg device (not supplied)
  • UK power supply (not supplied)
  • Serial-to-USB cable (can be supplied by YouChoos on request)
  • YouChoos' own software for creating, managing and loading sound projects to CT decoders (included in &25 license)
  • Full documentation (supplied digitally)

Download Software

Download Software

Anyone can try out this software for free by downloading the latest version from here. A license key is required to save projects, or to load them into a decoder.

User Guide

Download User Guide (PDF)

Download the User Guide for the YouChoos CT SoundProg application here.

Version History

Enhancements and Fixes

View Version History here, for a list of enhancements and bug fixes.

The YouChoos CT SoundProg application provides an easy-to-understand interface for configuration of CT Elektronik sound decoders, including an intuitive design for almost all aspects of the decoder's features - not just sound. Take a look at the screen shots below to get an idea of how powerful and simple this is...

Project details Edit individual CVs DCC loco address
Motor tuning and speed settings Function Outputs Steam sound schedule
Diesel/Electric sound schedule Callable sound effects Sound configuration
Function Key mapping Update decoder Firmware or load sound project