We have a group of very smart enthusiasts working on Airbus avionics. Today I received some help from Christoph and James to get the ATC transponder and Radio Management Panel turned on.
Christoph is the founder of Cockpit Concept and manufactures Airbus panels, ARINC interface boards, and other electronics. In addition, Christoph developed the CPDLC client for use with Jeehell FMGS (if you have not tried it out, what are you waiting for?) and also runs the FMGS Mantis Bug Tracker.
ATC Transponder, 115 VAC required
The ATC transponder requires 115 VAC to operate. Unfortunately this is not readily available and you will be required to purchase a static inverter to transform direct current into alternating current. Volker (another smart German 🙂 was very helpful in helping me find a 28V DC to 115 V AC inverter.
With Christoph help the LCD finally came alive. Although there has been some damage to the LCD screen (digits 1 and 2 not fully visible), it looks like it can still be put to good use in the sim.
James was able to provide me with the information that ‘SDI Code’ has to be connected to ‘SDI Code Common’ (whatever that means – update: James has informed these pinouts allow you to assign the RMP as either Captain, First Officer, or backup radio) for the RMP. When this was all linked up I was happy to see the RMP display in good working order. An additional ground wire was required for 8.33 KHZ function (European airspace).
Both panels will still require an interface board to connect and function with a simulator.
A320 RMP. 24-28 VDC required for operation.
Pinouts (incomplete)
ATC Transponder
Backlight 1/2 (5v)
115 vAC input 3
AC Ground 4
Radio Management Panel
24-28VDC Power Input N
Power Input Ground R
Assign RMP position (connect to each pin): L+K – RMP1 (Captain), J+L – RMP2 (F/O), J+K+L – RMP3 (Overhead backup)
8,33 KHZ Function X (connect to common ground)
Backlight (5v) T/U
Selection bulbs and SEL light 5VAC t/u (lowercase, RMP must be turned on)
Chassis Ground V
Light and Static Display Test S/Ground
Soarbywire 
Dear Ben,
Recently I have bought one of these items, and I am having trouble with looking for a 28V power supply to test it with. Do you think a 24V supply would also work or would that be below the circuit’s minimum voltage threshold?
Also if you are able to, then based on your experiences, could you please advise me on how many amps it draws when powered on, backlighting excluded? I would like to know what amperage I should go for when looking for power supplies.
Thank you for your reply in advance.
Kind regards,
Dávid
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Hi David, I have not tried with a 24V supply — it could possibly work; the A/P solenoid lock found on the sidesticks for example is rated at 28V but they also function at 24V.
I do not have the current draw for the modules as I am not at the stage of connecting them up for use with the simulator — however if you use a bench top power supply you could easily test if the modules work at a lower volt and what the total current draw is.
Regards,
Ben
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Hi Ben,
I’ve managed to borrow a 24V power supply from a friend so that I can test the RMP, and it really does work with 24VDC instead of 28VDC! Thanks for the suggestion. 🙂
Also while looking at some schematics, I’ve found a couple more pins which you may find interesting.
You’ve mentioned connecting 2 SDI Code pins together. On the schematic, there is one “SDI Code Common” pin and not only one, but TWO “SDI Code” pins.
L – SDI Code Common
J – SDI Code
K – SDI Code
The drawing shows all 3 pins, L+J+K connected together. I’ve tried a combo of L+J, L+K, and L+J+K, but I couldn’t see any differences. If someone who knows more about the SDI code pins could chime in on this and give us a better information, I’d be grateful! 🙂
There is also a “Light and Static Display Test” pin, lettered S, which has to be connected to ground. It turns on all of the segments at once, showing a bunch of 8’s.
Also, the backlight is intended to work with 5VAC. The pins are the following:
Pin T is 5VAC High, connected to the output of a 0-5VAC light controller.
Pin U is 5VAC Low, connected to ground.
And lastly, for safety purposes, I’d like to introduce pin V, which is called “CHASSIS GROUND”.The resistance between the metal chassis and this pin was around 28-32 kilohms for me.
Kind regards,
Dávid
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Sorry, I forgot to mention that 5VAC on lowercase “tango” and “uniform” pins will power up the green LEDs of the buttons, and also the SEL text.
Unlike the uppercase T and U (backlight) pins, you have to power up the RMP for it to work.
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Hi David,
Thank you for the additional information — the community will be grateful. I have added them to the pinout list for future reference.
I also tested with 24 VDC, and indeed it does work — 28V is hard to come by 🙂
Yes, the bulbs are rated for 5VAC, but they should have no issues with 5 VDC (simple circuit).
Re: SDI code — is a complex affair and best if James, or Christoph could answer. It is a necessity to wire as you probably found out, as the RMP will not turn on without them.
Regards,
Ben
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Hi Ben,
Thank you for adding the pins to the list! I will try to look at more schematics today to see if there are any other useful pins I could poke around with at home 🙂
Best regards,
Dávid
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Hi Ben,
I dug into the SDI code subject in my free time a bit, and I was told that (amongst other things) they serve the purpose of identification in the ARINC messages (via SDI Label). Also, certain channels are specifically assigned to be controlled by one of the 3 RMPs. For example, when an RMP selects a channel it’s not supposed to touch, like RMP2 selecting VHF1, the SEL indicator will light up.
After analyzing some schematics, I found out which SDI combos set which side.
L+K – RMP1 (Captain)
J+L – RMP2 (F/O)
J+K+L – RMP3 (Overhead backup)
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Well done David, I have confirmed these settings with James and will update the website. Are you also on the FMGS forum? We have other hardware we are trying to tackle and could also use your expertise. I am looking for a way to contact you. Regards.
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Hi Ben,
Thank you for including my pinouts! 🙂
I’m not sure if I have heard of the FMGS forum… I do have an unused account on mycockpit.org though, which has a section dedicated to Jeehell’s software, if you mean that. I will try to contact you either through Youtube or mycockpit tomorrow after work! But right now it’s almost midnight here so I should pack up my RMP and head off to sleep 🙂
Also, I would like to ask you something about those amphenol/cannon connectors that are everywhere on avionics. How do you interface your original parts’ pins to your controllers? Do you buy and solder your own plugs, or do you use some other method? Right now, I am using some simple header pin connectors salvaged from an old PC case. You know those cables you plug into the mobo, like switches, LEDs… It kinda works if I don’t move the wires/connectors, but I am terrified of accidentally breaking a pin due to the stress which may happen accidentally. Could you please advise me a cheap, but more secure/stable alternative? It would help me a lot, especially during breadboarding work on my ARINC429 USB interface gizmo.
I wrote all of this on my phone, so I hope autocorrect didn’t mess it up!
Thank you very much for your reply in advance. Have a nice day!
-David
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Hi David, I get asked this a lot so I’ll put up a post explaining the methods. I use dupoint connectors which are able to slide into the pin – they work well, are cheap and effective.
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Hi Ben,
Thank you for your reply! Yeah, I guess the old PC wires that I use are pretty close to Dupont.
Because 22-55 Amphenol connectors for my RMP would be far too expensive, I am currently experimenting with making my own connectors. I haven’t got access to 3D printing, so the prototypes are made out of hand-cut layers of plexiglass and wood. I ordered a bunch of female Dupont connectors from eBay, which I plan to use in this project.
The basic idea is to make a finalized 3D printed product with Dupont connectors placed into the drilled pin holes, so when you connect it, all the pins go into the sockets. So far I only have a basic 3D model of the shape, and I’ve yet to mark the holes. We’ll see how far it goes.
Best regards!
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