ArVeeNiner

ArVeeNiner

Well Known Member
I'm deciding on an intercom and before I do, I need to understand how to tie in the audible output from my Dynon AOA warning as well as the warning from my Zaon MRX.

I'm thinking that, without an audio panel, there are basically two ways to get audible alerts into my headphones. The first is to buy a 4 place intercom for my two place airplane and then tie the alert outputs to the Pax 3 and 4 inputs. Another way would be to buy a two place intercom and tie the alert outputs into my stereo input jack for my iPod. I'd splice them downstream from the jack. However, I'm wondering if tying into this jack would negatively effect the stereo operation.

I'm interested in what has worked out there.

Thanks

Kelly Johnson
RV-9A
 
Stark Speak

Wow...I'm actually addressing Kelly Johnson!

I had a very similar question and thought.....who better to pose my query to....on a popular but nevertheless public forum sure to contain often wildly differing opinion on virtually any subject....OR consult with a true avionics professional like John Stark? http://www.starkavionics.com/

So I asked "John, without an audio panel, how am I to hook unswitched audio to the PM1000 (2-place) intercom?"
The following is his response:

"Each intercom has a phone input. You will need to run each audio wire through a 220 ohm resister and then to the com phone audio input of the intercom. Nav, com, AOA etc. will run through its own 220 ohm 1/4 watt resister (you can pick them up at Radio Shack) and then to the com phones (radio) input of the intercom."
 
AeroElectric Bob Speak

From another expert.... A more complex, but elegant, solution from Aeroelectric Bob is a DIY Isolation Amplifier.

Basically it is the resistors in series approach listed above, but with better AC isolation, and a summing amplifier to isolate all of the inputs.

Stereo and Mono versions are shown.

http://www.aeroelectric.com/DIY/Audio_Isolation_Amplifier.pdf

I believe the circuit boards are available...

gil A
 
Funny, I just posted this on another thread.

If you are using an iCom, you can wire the Dynon audio out to one of the radio's three mono inputs. Then the radio goes to your intercom.

Here is my schematic.

I hope that helps.

I've been flying with it for 85 hours now and it works great.
 
Ahhhh, so Mr. Stark is saying that the alerts tie in with the input from the radio. Duh, of course! What I don't understand is why the need for the resistors...even on the radio input? The Dynon manual suggests installing a pot between it and the input which is indeed a variable resistor. Wouldn't that be a better option? You would be able to adjust the volume of the various alerts. However, I don't think you'd need that on the input of the radio because that already has a volume knob on it.

I bought an SL-40 based upon my 6 years of bullet proof experience with one in my Aeronca Sedan. Unfortunatly the SL-40 doesn't have aux inputs like the iCom has.

Regarding the Nucholls way, I was hoping for a simpler solution.

Thanks again.

Kelly "no relation to Clarence" Johnson :)
 
Kelly.

It's quite acceptable to add several audio alarm sources to the radio bus as long as they are all combined using series resistors (including the radio). The resistor values are not critical, but I use 510 ohms.

For any audio source that does not have a volume control setting, you should have a variable resistor (aka potentiometer) in series or shunt.

For my D10A, I used a 100K ohm linear taper potentiometer in series. Dynon put an audio test function into the D10A so that this could be adjusted on the ground.

Perhaps the best way to understand all of this is to look at the schematic in the back of this document from Vx Aviation.

You may not want to use the Sigtronics intercom, but the same principal applies to summing the audio sources. You can wire up a bunch of resistors on a D-sub connector to accomplish it.

Vern
 
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I had exactly the same problem.
Dynon and Garmin Sl40.
My solution was a resistor on the Sl40 output, then the dynon wired through the variable resitor to the headset jack's. We played around with a couple of resistors to find what balanced out best. Seems to work ok now.

Peter
 
So, I went to the source, John Stark, as well and this is what he said:

"Concerning the adding of 220 ohm resistors in line with each audio input connecting to the comm audio input of an intercom (including the comm input itself): This is done for impedance matching. If they all have a minimum of 220 ohm resistance this will prevent any one of the inputs you are using from dominating the input. If any input doesn't have at least 220 ohm of resistance the electricity will follow the path of least resistance and go mainly to that one input you didn't load with the 220 ohm resistor. The unloaded input would be really loud and the loaded inputs would be really low. But don't the inputs already have some resistance? Yes but since they are all different you are sure to have one taking all the input current. If your audio input doesn't have a way to adjust the volume then you may put a adjustable resistor (potentiometer) in line IN ADDITION to the 220 ohm resistor."

So physically, how do I do this? So I have this wire coming from the radio. Another from the Dynon, and a third from a Zaon MRX.

Taking one of the wires as an example, I put a resistor in line with it. I assume I can just solder it and shrink tube it to the wire. I do this for all the wires. Then, they all tie together down stream from the resistors then into the intercom. Is this right?

On those inputs that have no volume control, I'll put a pot somewhere either before or after the resistor.

Maybe I can get a circuit board and solder the resistors to it. Three wires in, one wire out. Sound good?

These electrons scatter my brain sometimes.
 
So our audio output is a 16.8 V p-p AC coupled signal.

The reason we suggest the 10K variable is so that you have a volume control.

Typically you want to tie into the aux audio input of your intercom, but if you don't have one, some intercoms allow for this signal to be fed into a mic input. Just bear in mind that you may have to contend with a squelch circuit on the mic input that may chop the signal. Someone experienced this with the PSM3000 recently.

Our audio output in not stereo...of course...so keep that in mind as well.

Does that help?
 
Dear Kelly:

The PM3000A is a stereo intercom that has 2 unswitched inputs. These inputs would work well for the Dynon AOA and the Xaon MRX audio signals.

www.ps-engineering.com/pm3000.shtml

Hope this helps

Mark Scheuer
PS Engineering, Inc.
www.ps-engineering.com

ArVeeNiner said:
I'm deciding on an intercom and before I do, I need to understand how to tie in the audible output from my Dynon AOA warning as well as the warning from my Zaon MRX.

I'm thinking that, without an audio panel, there are basically two ways to get audible alerts into my headphones. The first is to buy a 4 place intercom for my two place airplane and then tie the alert outputs to the Pax 3 and 4 inputs. Another way would be to buy a two place intercom and tie the alert outputs into my stereo input jack for my iPod. I'd splice them downstream from the jack. However, I'm wondering if tying into this jack would negatively effect the stereo operation.

I'm interested in what has worked out there.

Thanks

Kelly Johnson
RV-9A
Click to expand...
 
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