737 ATC Transponder
For flight sim developed by Opencockpits
Reviewed by Jack Whaley-Baldwin
February 2010

"Opencockpits" The word probably, for most of you, doesn't ring a single bell.  Countless forums members, Just Flight, Aerosoft and even here on Mutley's will probably all raise eyebrows when you mention the word.  Not many people have heard of Opencockpits – But I have, and I'd like this review to give you a full insight into them, their 737 Transponder and their software.

The Company
Lets start with the facts. Opencockpits are a group of Spanish flight simulation hardware suppliers that formed in 2002. They have a dedicated support team, about fifty hardware products on sale, a forum and extensive relationships with other sites (Flight Sim Labs Ltd, MyCockpit.org and others).

Even though they are Spanish and English is obviously not their native language, their support team does a very good job at translating languages from all over the world to answer Support/Sales queries.

Opencockpits charge prices that are much cheaper than other companies. For example, the Transponder used in this review was purchased (including Shipping & VAT) for £149.99, whilst the nearest competing product would've cost about £40-50 more.

A good bonus is that their store is PayPal Verified and they will accept all common forms of payment (Visa, Mastercard etc). This means that you'll not only be getting a good price, but a secure transaction too.

My Research & Enquiries
When I first cast my eyes upon the FS transponder hardware market, I had a wide choice. Elite, Saitek, Cockpit Sonic, Simkits... You name it, I could've chosen them. Fortunately though, a few weeks previous I had already had a quick glance over Opencockpits' website, and I remembered that they had a transponder module on their site. I quickly rushed over to them and took a look at the product description.

Despite not only being cheaper than the other companies, their transponder looked much more like an “airliner” transponder (I wanted this as I'm building a Boeing 747-400 pedestal which obviously requires a Boeing-style airliner transponder).

Their price and looks sold it to me – But what about compatibility? I emailed their support a few times, questioning the products compatibility etc, and they assured me that the transponder is FULLY compatible (this means that everything works – The ALT source, transponder codes, transponder modes... The lot!) with the Level-D 767 (through an extra free piece of software called “lekseecon”) and partially compatible with practically all other add-ons (this means that it will only change the transponder code itself, but I really didn't care as the other transponders (Elite, etc) didn't do much more than this anyway) such as 757 Captain, PMDG 747-400, CLS 747 etc.

With all my potential questions and issues sorted, I did not hesitate to buy the product (I bought from Aviation Megastore – Which is the only official Opencockpits hardware retailer apart from Opencockpit themselves). I purchased the version with Orange Digits. There is a White Digit version available too.

The Product Itself
On a Friday evening, FedEx delivered a lovely looking package which I eagerly opened. Low and behold, a securely packaged Opencockpits 737 ATC transponder was inside. I immediately took it out the box, and began to read the documentation (not much came with it, probably because most of the documents can be downloaded in PDF from Opencockpits' Site).

The Transponder allows the adjusting and configuration of the following:
– Transponder source
– ALT source
– Transponder squawk code
– Transponder mode
– INDENT button
– Transponder red fail light

I plugged the transponder in via a USB Socket in my computer... And was almost blinded by the incredible backlighting that Opencockpits provided. I mean WOW! By no means is this a downside – The strong backlighting is necessary as there is a thick layer of material between the backlights and the actual panel front. Please look at the diagram I drew below for more clarification.

The Transponder -Configuration
Once the module is plugged in, you'll notice that although thebBright backlighting is working, there is absolutely no other display apart from the “Transponder fail light” illuminated in red.

To get a display, we need to actually get the PC Interfacing with thetTransponder via Opencockpits' “IOCModules” Software.

IOCModules is a completely free program that will automatically be installed if you download the transponder “files package” from Opencockpits' website (remember all software is FREE).

Beforehand, you must make sure that the latest version of FSUIPC is Installed or else it won't work.

If all is installed correctly, you should see on yourdDesktop (or elsewhere, depending on the directory you installed the “IOCModules” software to.) a program entitled “IOCModules”.

Double clicking the icon will bring the program up. As of January 2009, version 1.6 is the latest version. It is a very simple program to use.

When your transponder is plugged in via USB, the IOCModules program will allow you to adjust certain things on the transponder such as the brightness of the digit display at the front.

Below is an annotated diagram of the “IOCModules” program as it will appear if you have FSUIPC correctly installed, correctly Plugged in and “IOCModules” program correctly installed.

Once one is comfortable with everything, the next step is to fire up FS2004/FSX/X-Plane (Yes! Something that works with all three simulators!). Choose a flight (obviously with an aircraft that has a transponder!) and load up.

Once loaded, you are free to do whatever you want with the transponder. Please note, unless you are running the Level-D 767 you can only adjust the transponder squawk code. To adjust the Code, the knob on the LEFT will control which number you are adjusting, and the knob on the RIGHT will adjust the actual value. For example, say I wanted the Squawk Code “7537” -I'd do this:
Adjust first number to 7 using RIGHT Knob > Turn LEFT knob once to get to the next number > Adjust second number to 5 using RIGHT knob > Turn LEFT knob once to get to next number > Adjust third number to 3 using RIGHT knob > Turn LEFT knob one final time to get to final number > Adjust number 4 using RIGHT Knob to 7 > You will end up with Squawk Code 7537

And that's the gist of controlling the transponder. If you own the Level-D 767, you'll also be able to adjust ALT source, XPNDR Source etc.

The transponder is perfect for VATSIM Flight. It's great to have a “hands-on” experience whilst the controller is reading your squawk code. Just adjust the code into the transponder and you're away.

The transponder also works with GA aircraft add-ons such as Carenado's PA34 200T Seneca.

The Transponder – Biology
What is the transponder made of? Factory parts? Hand crafted goods?

The transponder has been designed using Opencockpits' own range of hardware products (their own PCB, their own rotary knobs and display etc), and then put together by hand by their engineers.

Because Opencockpits' don't have a factory, all their products are handmade. This is great, because the attention to detail applied is incredible.

For example, the soldering between joints is very well done. A good, solid bond is applied, not just a cheap quick done join that would break within a few hours. The transponder is made to last.

The SIOC Software
NOTE: If you are just interested in the transponder product alone, please skip ahead to the “Final Thoughts” summary at the end of the review.

The SIOC software is a program made by Opencockpits. It is free of charge, however if you wish to use it commercially, say in a flying school, you must pay the small fee to do so.

SIOC is a complex program that allows you to write certain “scripts” for hardware. For example, if you wanted to use the transponder in a special way with a special add-on, you'd have to hand-write a SIOC Script (which takes hours and hours of typing and clicking), and then finally compile and run it all using SIOC.

Now, for some of you, you probably got lost somewhere in that sentence!  Don't worry – SIOC isn't necessary for the operation of the transponder (unless you want to run it in a special way – Not many people do though).

Take a look at the SIOC Interface Dialogue Screen below.

Overall summary of Opencockpits' transponder module, brilliant!

Whether you're a VATSIM flyer or a casual simmer, the transponder module is great for everything. The backlighting is an extra bonus, making it useful if you fly in a dark room. The realism is excellent, owning to the fact that every switch and knob is modelled.

Well done Opencockpits!


  • Very realistic looking Module
  • Great looking, crisp LCD display
  • Fail light
  • Great backlighting
  • Amazing price
  • Good support
  • ALL software required is free


  • 1 Only FULLY compatible with the Level-D 767

My score? 9.5/10

/Jack Whaley-Baldwin

Useful links

http://www.opencockpits.com    Opencockpit's Website (IOCModules and SIOC are located on this site)
http://www.schiratti.com/dowson.html FSUIPC
http://www.lekseecon.nl/lekseecon.html   Lekseecon by Nico Kaan