Dynon SV-Intercom-2S and ATR833

[Steevo25]

Hi All,

Hopefully someone can help me out here as I am completely perplexed by a problem I have.

Originally, I had a Funkwerk ATR833 radio and a Flightcom 403 intercom. I needed some more audio inputs and the Dynon intercom seemed exactly what I needed.

It was installed last weekend and I have spent the last week trying to solve a specific problem and am now at the end of the road.

There are only 3 wires that go between the ATR833 and the intercom. Headphone, MIC and PTT.

PTT pin 15 on ATR to pin 12 on Dynon

This is what seems to be the problem. When this connection is made, the LED on the front of the Dynon goes dim and although I can transmit and receive, I get a squealing noise like feedback when I transmit. Receive is perfect.

The dim LED happens as soon as the 25 way connector for the ATR is plugged in to the radio. The radio does not even have to be on.

If I take off the PTT pin then the intercom is normal. Both the intercom and radio are fine (except a dim LED)until a PTT is pressed then the squealing starts while it is pushed.

I have checked, double checked and triple checked the wiring and I am 100% sure it is correct. The same radio was working fine with the Flightcom and this week I tried a PS engineering intercom as well which works fine. They all use the same 3 wire connection (different pins of course). I am only having the issue when the Dynon intercom is used.

To summarise,

Both radio and intercom work fine when completely separate.

When the radio 25 way connector is plugged in to the ATR and the PTT wire is connected between the two devices, the LED on the Dynon goes dim and there is a squealing noise when PTT is pressed.

I am really hoping someone can come up with an answer or tell me something I am doing wrong. It almost seems as if the intercom is not compatible with the ATR. I have spent hours changing intercoms and rewiring but the fault persists when using the Dynon. The Dynon, for some reason, does not like the PTT connection from the radio.

Many thanks in advance.

 

[davedubb]

A few things that may help us help you.

1. What voltage is your system?

2. What gauge of wire are you using for both power and ground?

3. Approximately how long is the wire run to the intercom?

3. Is it possible for you to hook up the power directly to the intercom? (both + & -) If you have a separate power supply that would be even better.

You mention that the LED goes dim and this may be an indication that the whole system is not getting the proper power requirements. This could be because of voltage drop from either wire gauge or wire length. Odd things begin to happen in audio systems when power requirements are not met and this may explain the noise on transmit where power requirements are the highest.

Feel free to call Dynon Tech Support by phone as this may be a better option for solving your problem if your testing does not fix the issue.

 

[cessnadriver850]

Being an old time (I mean old) avionics guy, there have been ocassions with some radios where a diode needs to be placed between the radio and intercom and or audio panel in the PTT line. Make sure the arrow or pointy end of the triangle on the diode points toward the radio.

 

[Steevo25]

Sorry I have taken a very long time to reply to this. I did check back a couple of times and there were no replies and I didn't get an email to inform me of a reply.

Ok, the whole system works on 12v and the cable length between the intercom and radio is about 6 inches. The distance to the power and earth busses is about 10 inches. I am using 16awg cable for all power and earths and 22awg cable for everything else.

This seems to be some incompatibility with the Dynon and a non sky view system. I have tried it with the ATR833, a Microair and also an MGL V6. In all cases, as soon as the PTT cable is connected between the intercom and any of those radios, then the LED on the Dynon Dims. The squealing was an unrelated issue and was purely to do with the shielded cable.

I took it all out the aircraft and installed it on the bench with a new wiring harness and the same thing happens with all those 3 radios. In the end i had the intercom replaced and the replacement does the same thing.

Also, with it all wired in and the radio switched off, the auto mute does not work. As soon as you switch the radio on, the auto mute starts to work (this is using the music in socket).

I am 100% sure all wiring is correct. I tried a diode both ways around and one way prevented the PTT from working at all and the other way made no difference. I also tried various resistors on the PTT wire between the intercom and radio but that made no difference.

The only way I have got it working is by using a relay. The PTT wire of the intercom now earths a relay which in turn earths the PTT input on the radio. In this configuration both radio and intercom work perfectly. The LED is the correct brightness and the auto mute works whether the radio is on or off. This configuration works with all 3 radios. But on any of those radios, if I remove the relay and connect the PTT pin on the intercom to the relevant PIN on the radio then the LED goes dim and auto mute will not work until the radio is switched on. If I pull the connector out the back of the radio, the intercom function returns to normal.

Is anyone using the Dynon intercom with a non Dynon radio?

 

[Dynon]

Sorry for our delay in responding to this. We wanted to get your symptoms in front of some expert eyes. It looks like the remaining unresolved issues are the dim intercom LED and auto mute not working.

We have two things that we'd like you to double-check:

1) The two shielded cables between the intercom transceiver should be terminated at the intercom side only. The shields at the transceiver must NOT be connected to the transceiver ground.

2) The transceiver should not be grounded to the airframe. The only ground connection to the transceiver should be through pin 1 of the intercom.

Both of the the above are stipulated in our installation guide. I know you said you are 100% sure that the wiring is correct but we want to explicitly eliminate these possibilities. We suspect that the relay on PTT solved the problem because when you installed the relay you broke the ground loop between the intercom and the transceiver.

 

[Steevo25]

Hi There

Thank you for your replies. I think the best way to explain my wiring is to say how it was when I had it on the bench running from a 12v battery. This is much simpler wiring for demonstration but the results are the same. In the aircraft I can confirm that all shields are connected at the intercom end and only at the intercom end. When I removed it and bench tested it, I had the wiring as follows (I used standard wire not shielded on the bench). This was tested with my Funkwerke ATR833 but the results were the same with other radios, just different pins on the radio side.

Int pin 13 to 12v
Int pin 1 to battery gnd
Int pin 1 to ATR pins 13 and 25
ATR pins 11 and 12 to 12v
Int pin 14 to ATR pin 2
Int pin 25 to ATR pin 19
Int pin 12 to ATR pin 15

It's the last connection that causes the LED to dim. It dims further if you turn the radio off but leave the d-sub connector plugged in. If I remove the d-sub connector from the radio or remove the wire going from Int pin 12 to ATR pin 15 then the led goes back to normal.

I didn't find out about the auto mute until later on but in the above configuration, the auto mute will not work unless the radio is switched on or the D-sub connector removed from the back of the radio (obviously to test the auto mute I had to wire in some headphones).

 

[Steevo25]

Just for further information, I think I have discovered what is causing the issue. I was doing some testing using my previous Flightcom 403 and my Sigtronics 200S and it seems that the Dynon outputs 12v on its PTT wire when the PTT switch is NOT pressed and then provides ground on that wire when the PTT switch IS pressed. Both the other 2 intercoms only provide a ground when the switch is pressed otherwise open circuit.

It seems, at least the 3 radios I have tried, do not like that 12v and that is what causes the problems. This is why the relay works as it isolates that 12v from being presented to the radio's PTT signal. It seems the radio is objecting to that 12v which is causing an upset to the Dynon intercom as well.
I only noticed this because today I turned off my radio but the backlight on the LCD display remained partially lit and I could not understand why. As soon as I pulled the connector from the back of the Dynon, the radio went completely off.

It appears that the only possible way of interfacing the Dynon to any of the radios I have is to use something like a relay.