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DIY Audio Panel and Radio Head. Crazy?

Flying Canuck

Well Known Member
Patron
I'm starting to think about upgrades on my RV-9A, inching toward IFR capabilities. One of the first things I'd like to do is add a second COM. Now, I like to tinker and sometimes I come up with ideas that should never see the light of day. My current idea might be one of those so I thought I'd put it out there for comment.

The first problem that comes up with the second COM (and a future NAV radio) is the need for an audio mixer or panel. As we all know, audio panels are painfully expensive. Mixers are much less feature rich and more reasonable in price. Here is my idea - using a Raspberry Pi, a whole lot of relays (26) and a small LCD touch screen I could build an audio panel. The Pi would present the various selector buttons (RX COM1/COM2/NAV, TX COM1/COM2) and drive the relays for simple connections from my radios to my headsets and from my mics/PTT to my radios. This isn't all that complex and would cost less than 10% of a new audio panel. The relays are bundled on small cards, 8 at a time. I would design it so that my COM1 is connected via normally closed circuits so that if I lose this contraption I still have COM1 working in both directions.

The second opportunity here is for a COM controller. The MGL V16 comes as a remote unit and you can add a variety of heads to operate it. Their interface is published and very well documented and if you can connect RS232, you can control it. Now, I've had some success with connecting RS232 to a Raspberry Pi - I know I can do that. Writing the little bit of code to make a front end interface for the radio is well within my experience. This could go on the same Raspberry Pi and same small touch screen as the audio panel. This comes with no incremental costs (I already have the DB9-USB dongle for the serial connection) and would save a few hundred dollars as well.

All told, this project could save me 2 AMUs. It would all be for backup avionics so I could tolerate complete failure. Anyone have any reasons that this might be too crazy? Or that something that I described would not work?

Bonus material - any reason that I wouldn't want to install my second COM antenna under my wing, maybe 3' out behind the fuel tank? Just aft of the inboard access plate?

I know, too much time on my hands.. Thanks for any 2 cents out there.
 
On my 6, I used a 4PDT (on-on) and DPDT (on-off-on) switch. 4PDT switch is com 1 / com 2. DPDT has center normal, top non selected com monitor and down is Nav monitor. 4th pole is used to send the offline headset output to the DPDT.

You can monitor the non-selected com, the nav feed or turn the monitoring off. It feeds into the unswitched audio (need two of them if you also have EFIS alerts). My PM3000 had two.

No mixer necessary, just can't monitor both coms AND nav. Though not sure when that would be necessary or even feasible. I struggle monitoring 2 coms.

Larry
 
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On my 6, I used a DP4T (on-on) and DPDT (on-off-on) switch. DP4T switch is com 1 / com 2. DPDT has center normal, top non selected com monitor and down is Nav monitor. 4th pole is used to send the offline headset output to the DPDT.

You can monitor the non-selected com, the nav feed or turn the monitoring off. It feeds into the unswitched audio (need two of them if you also have EFIS alerts). My PM3000 had two.

No mixer necessary, just can't monitor both coms AND nav. Though not sure when that would be necessary or even feasible. I struggle monitoring 2 coms.

Larry

Is there a way for you to just switch the 2 radios with only 1 switch (no nav monitoring needed) ?

Example:
Radio #1 on 123.0
Radio #2 on 122.8

I can monitor my both frequencies on radio #1 with its monitor function so if I hear something I need to answer on the second frequency I can flip the switch and now I’m using radio #2 ?

Sure I can just touch the swap button on radio #1 and I’m on the second frequency but I want 2 radios for redundancy so I might as well have an easy way to switch to the second one if needed and that switch would do just that.
 
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These kinds of projects certainly aren't to reduce cost and save time... but they are sure fun.

If it helps, you can build audio panels out of some of this stuff. I no longer make it, but it was all in production at one time and is still current.

V
 
These kinds of projects certainly aren't to reduce cost and save time... but they are sure fun.
V
Well, I'd say they save cost as long as you value your time at $0.

I have a home-brew "audio panel" in my plane. I put it in quotes because it's really more of an intercom, with lots of unswitched inputs. IMHO there is just less need for switching than there used to be.
1. I have an SL-30 that has a front panel button, to enable hearing the VOR/ILS audio. It's wired to an unswitched input on the "audio panel".
2. No MB, ADF.
3. One DPDT switch to switch the mike and PTT lines between #1 and #2 com.
4. I need to manually turn up the com volume if I switch coms. But in actual operation, both VFR and IFR, I seldom use #2 for transmitting.*
5. I hard wired (unswitched inputs) EFIS warnings, traffic call outs. I cannot, and do not want to, mute these.
6. I have a stereo XM radio input, sound quality is good.
7. I have a lot of volume controls, so I and my passenger can adjust radio, intercom, music volumes to our own desires.
8. Intercom. Here's where the rubber hits the road, so to speak. My intercom is definitely understandable, but the quality is not up to, say, a good PS panel. My version uses strictly analog filtering for wind/prop noise, while I think PS uses high quality (and expensive) FFT and frequency domain techniques that are beyond my capability. Also, I have a manual squelch circuit, not "auto squelch". But in practice I seldom touch the knobs, unless a passenger plays with them.

The whole thing is built with inexpensive OpAmps. Just one relay (for fail-safe feed thru of #1 com). The knobs are the single most expensive part.

Send me your email if you want a copy of the schematic.

* I currently have a gentleman's bet with another poster, over how often he will use a transmitter select switch. (I claim #2 is almost never used for transmit). He disagrees, but has already said switching will occur on the ground, not when airborne. But, clearly "auto switching " the audio outputs can be done with just a bit more work.
 
GTR200 has three physical audio inputs + bluetooth and internal stereo intercom. Each input's levels are adjustable. I've wired this radio with a 2nd com and other audio inputs. A simple DPDT switch controls the PTT lines. Tie the transmit interlock lines between the radios and voila, no need for any sort of audio panel.
 
Is there a way for you to just switch the 2 radios with only 1 switch (no nav monitoring needed) ?

Example:
Radio #1 on 123.0
Radio #2 on 122.8

I can monitor my both frequencies on radio #1 with its monitor function so if I hear something I need to answer on the second frequency I can flip the switch and now I’m using radio #2 ?

Sure I can just touch the swap button on radio #1 and I’m on the second frequency but I want 2 radios for redundancy so I might as well have an easy way to switch to the second one if needed and that switch would do just that.

Yes, a simple 3PDT (on-on) switch will work. Use a common ground and run the phones, mic and PTT lines of each radio to each throw contact and the center/common goes to the intercom.
 
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Yes, a simple 3PDT (on-on) switch will work. Use a common ground and run the phones, mic and PTT lines of each radio to each throw contact and the center/common goes to the intercom.

Thanks, I?ll print this for future use.
 
As an avionics guy I will say that a lifetime of working on aircraft has left me with the very firm belief that the best money you spend on avionics is spent on buying the best audio panel you can get, then spending the time and money to install it in the very best possible fashion without a single corner cut.

While I applaud the homebuilder spirit exhibited in this thread, I will cautiously say that once you've had your fill of hiss, whine, audio popping sound of relays making and breaking, etc, you'll eventually install a good audio panel and be done with it.

Start with the most panel you can afford in the PS Engineering lineup, install it in strict accordance with their instructions, and never look back.

For those who would think I'm gung-ho about spending other people's money, my airplane features a PDA360EX panel. Terrific audio. Zero problems. Bliss.
 
Related to the mention of the V16 COM radio and its open protocol.

The N16 NAV radio is also open in the same way.

The A16 intercom is also open but I have not yet found the energy to document the protocol. However if there is interest I shall do so fast. Note there is also a compatible A14 intercom on the way (half the size, single circuit stereo with Blue tooth and ditches two mono inputs). Still does all the interfacing to two COM radios but instead of having 4 wired AUX mono and 1 stereo input it has 2 wired mono AUX inputs and the wired stereo as well.

The protocol is slightly more involved compared to the V16/N16 as you can control so many aspects of the A16/A14. But that is mostly setup stuff - set input and output attenuators and gains and enables for what you want to use. During operation all you do really is switch inputs on/off, set volume levels and things like join/separation of inputs between pilot and pax circuits (in case of the A16, the A14 has a single circuit). The BT works nicely for music streaming and phone use so for phone use there is support in the protocol for receiving calls (i.e. hangup and accept or reject), or making calls etc.

Let me know if there is any interest in the protocol - I'm an old DIY'er and DIY everything (much to my Wife's annoyance ;-). So I am always happy to support DIY efforts.

Rainier
CEO MGL Avionics
 
As an avionics guy I will say that a lifetime of working on aircraft has left me with the very firm belief that the best money you spend on avionics is spent on buying the best audio panel you can get, then spending the time and money to install it in the very best possible fashion without a single corner cut.

While I applaud the homebuilder spirit exhibited in this thread, I will cautiously say that once you've had your fill of hiss, whine, audio popping sound of relays making and breaking, etc, you'll eventually install a good audio panel and be done with it.

Start with the most panel you can afford in the PS Engineering lineup, install it in strict accordance with their instructions, and never look back.

For those who would think I'm gung-ho about spending other people's money, my airplane features a PDA360EX panel. Terrific audio. Zero problems. Bliss.

It's a valid comment but then you should really not be building an aircraft yourself. I would presume you build an aircraft because you have the ability to do so and enjoy the challenge.
The very same goes for avionics and there have been a few threads recently even on making your own EFIS systems. Again - if you have the ability and enjoy that type of thing - why not ?

Obviously if you have two left hands you should go and buy a ready made aircraft and if you don't know how to use a soldering iron your should buy your avionics and preferably have it fitted professionally (as you point out quite correctly, audio wiring can only be done in two ways: Right and wrong. And it can still catch you out even if you know what you are doing).

I have great respect for those that build their own aircraft (and have seen some amazing work). The same goes for those that build their own avionics.

Rainier
CEO MGL Avionics
 
Related to the mention of the V16 COM radio and its open protocol.

The N16 NAV radio is also open in the same way.

That's an interesting thought. I knew you had the N16 but ACS doesn't carry it so I hadn't considered it. I could use my DIY control head to manage both devices and save some panel real estate. This is much simpler than the audio switching - probably go a bit more low tech for that.
 
That's an interesting thought. I knew you had the N16 but ACS doesn't carry it so I hadn't considered it. I could use my DIY control head to manage both devices and save some panel real estate. This is much simpler than the audio switching - probably go a bit more low tech for that.

It tends to take time until ACS lists a new(ish) product. They are in stock with MGL Avionics distributors in California. They also have the A16 (not sure if they still have any left, you may need to check but we are just now shipping another batch to them).

Rainier
 
There are many ways to make a two way radio switch panel. The most simple is one mic switch between COM 1 and COM 2. The audio can be mixed a few ways.

One way is an audio mixer so you hear both always and to mute one of the two radios is turn the volume down on that radio. The circuitry is very simple, few components and can be soldered together in an hour. If you google two channel audio mixer diy kit.... for less than $16 you can get something like below for the audio....

Another way to get audio from two COM's is by using one radio as master which has an AUX audio in, and feed it with the second COM.

s-l1600.jpg
 
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The very same goes for avionics and there have been a few threads recently even on making your own EFIS systems. Again - if you have the ability and enjoy that type of thing - why not ?

Rainier
CEO MGL Avionics

Rainier - your comment goes right to the heart of the matter. My comment about buying the best audio panel you can get is a clear summary of years of experience working on aircraft and discovering that even major avionics companies don't have what it takes to build really good audio products. Very, very few homebuilders have the capacity to make truly good audio circuitry.

Sometimes we build things because we want to, sometimes because we can. Sometimes we need to acknowledge that others have spent decades perfecting a craft and we're better to part with our cash to buy their products rather than live with a sub-standard result. Since we have a headset clamped to our head for the entire duration of every flight, good audio is one of those places where the vast majority of homebuilders would benefit greatly from buying the expertise perfected by acknowledged industry leaders rather than trying to brew our own solution.

By the way... by far and away the greatest number of contacts I receive from aircraft owners looking for avionics help are owners struggling with audio issues. My opinion hasn't been formed in a vacuum, but it's my opinion, worth less than the paper it's (not) written on! :eek: :D
 
As an avionics guy I will say that a lifetime of working on aircraft has left me with the very firm belief that the best money you spend on avionics is spent on buying the best audio panel you can get, then spending the time and money to install it in the very best possible fashion without a single corner cut.

While I applaud the homebuilder spirit exhibited in this thread, I will cautiously say that once you've had your fill of hiss, whine, audio popping sound of relays making and breaking, etc, you'll eventually install a good audio panel and be done with it.

Start with the most panel you can afford in the PS Engineering lineup, install it in strict accordance with their instructions, and never look back.

For those who would think I'm gung-ho about spending other people's money, my airplane features a PDA360EX panel. Terrific audio. Zero problems. Bliss.

Totally agree with the above, been there done that with 4PDT switches and homemade "audio mixers".

I personally am a fan of the GMA245, great value and works superbly.
I have heard many comments from passengers/customers of how good/clear my audio sounds.
Good radios and a good audio panel make all the difference.
 
There are many ways to make a two way radio switch panel. The most simple is one mic switch between COM 1 and COM 2. The audio can be mixed a few ways.

One way is an audio mixer so you hear both always and to mute one of the two radios is turn the volume down on that radio. The circuitry is very simple, few components and can be soldered together in an hour. If you google two channel audio mixer diy kit.... for less than $16 you can get something like below for the audio....

Another way to get audio from two COM's is by using one radio as master which has an AUX audio in, and feed it with the second COM.

Thank you !!!
 
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