Author Topic: Wired Audio PAW to Intercom volume control  (Read 2547 times)

riverrock

Wired Audio PAW to Intercom volume control
« on: November 02, 2020, 01:07:45 pm »
I'm planning two PAW Rosetta installations for group aircraft (some individuals will use their own tablets, other wont) so plan to pipe audio into the intercoms of the aircraft (one a Sigtronics SPA-400, one built into Trig COM).
Firstly, I assume that the Pi audio output is powerful enough to go into the Aux input of these?  That doesn't appear clear from various threads (and whether the Pi audio can be software boosted).

Secondly, to be able to suppress alerts in the circuit, I need a volume control.  My ideal would be a single knob which controls power to the PAW (initial "click") then adjusts volume, in a similar way to a Garmin COM. Even better if the knob was illuminated to show power was getting through the switch.  Any particular suggestions?  What potentiometer Ohms is required? One aircraft is 12V, the other 28V. If I can't find a suitable dual purpose knob, I could separate out power to a simple toggle.

Young_C

Re: Wired Audio PAW to Intercom volume control
« Reply #1 on: November 02, 2020, 04:01:27 pm »
Hi riverrock,
With our Rosetta permanent installation we piped the audio onto the "Music 1" input of our Garmin GMA240 audio panel (see photo attached, top left button). This was done by plugging a 3.5mm audio jack plug into the Rosetta and cutting and wiring the red and black wires directly into the GMA240.

This works well, the volume from the Rosetta is loud enough (BTW I don't think there is a way of adjusting the output level from the Rosetta) and controllable via the volume knob on the audio panel if necessary. Also we can suppress the alerts by toggling the Music 1 button if necessary.

Sorry I'm not familiar with the intercoms you have, but would expect that their Aux inputs would work with at similar voltage levels to ours.

Good luck,
Chris.

steveu

Re: Wired Audio PAW to Intercom volume control
« Reply #2 on: November 04, 2020, 10:27:13 pm »
This works well, the volume from the Rosetta is loud enough (BTW I don't think there is a way of adjusting the output level from the Rosetta)

Config page, along with the volume/audio output test button? Don't forget to save...

riverrock

Re: Wired Audio PAW to Intercom volume control
« Reply #3 on: November 05, 2020, 01:42:53 am »
Thanks, I'm thinking about something like this, the switched version, using the switch on the power supply before the transformer and the volume for, well, volume.
https://www.ebay.co.uk/itm/1K-ohm-Single-Mono-Log-Logarithmic-Lin-Linear-Switch-Pot-Potentiometer-And-Knob-/182322432827

exfirepro

Re: Wired Audio PAW to Intercom volume control
« Reply #4 on: November 05, 2020, 09:13:38 am »
Hi riverrock,

I’m not familiar with the specific setups of the intercoms you are dealing with. There are so many different systems out there, which is why we have never produced any specific documentation on connection of audio out from PilotAware, though there is a vast reservoir of information available on the Forum. A search using audio out from the Forum Home Page should find most of it.

A few general points.

The audio output from PilotAware is via a 4-pole TRRS socket on the inbuilt Raspberry Pi Motherboard - wired (from the  ‘tip’ of its 3.5mm jack plug) left audio/right audio/Ground/video out (there is no signal on the video, so a standard 3-pole TRS ‘stereo’ jack plug can safely be used).

The PAW audio output is in fact mono - with identical signal on both left and right channels, so a mono feed can if required be derived from either left or right channel + ground. There is BTW no advantage to be gained by combining right and left as a single signal. See this thread and others linked from it...

http://forum.pilotaware.com/index.php/topic,420.msg6959.html#msg6959

The audio level is set at its maximum within the Pi. As previously advised this is adjustable downwards in PilotAware/Configure, but for safety reasons (to do with potential hearing damage) can’t be increased within the PilotAware beyond the level set by the Pi. If there is insufficient volume to power your specific intercom, you can however use a simple audio amplifier to boost the signal if necessary. An example is referenced below, though I have also used a simple low-gain mono amplifier on one occasion (from Maplin - though other examples are available on E-bay).

http://forum.pilotaware.com/index.php/topic,1507.msg16904.html#msg16904

If you feel the need to be able to reduce the audio signal, e.g when experiencing a high level of traffic, this can be done by means of a simple circuit incorporating a potentiometer, but if adding a switch, be very aware of the risk of it being switched off and then forgotten. IMO it’s  much better to allow the volume to be reduced, but to maintain a minimum level of audio as a reminder to turn it back up again later. Also, if I read your OP correctly, you were suggesting using the inbuilt switch to control the power feed to the PilotAware - IMO a very BAD idea - if this is accidentally switched off by someone in a rush to turn down the volume, you will lose all your traffic (and probably position) information until the mistake is noticed and the unit is switched back on and has time to reboot and re-obtain GPS fix - so definitely NOT recommended.

Another alternative to combine and control audio is to use a commercially available audio mixer (such as those available from Maker Hart, which allow combination of audio alerts from (for example) PilotAware and SkyDemon, with easy level matching and ‘instant’ volume control via an audio master level slider or single knob. I know several installations (including my own) using this type of device very successfully.

Hope this helps. Please let us know how you get on.

Best Regards

Peter

riverrock

Re: Wired Audio PAW to Intercom volume control
« Reply #5 on: November 05, 2020, 12:05:10 pm »
Thanks
I found various posts but not one place where all the information has been gathered or whether consensus had been reached.
I'll plan to take one of the audio outputs from the Pi.  I had assumed I'd get better output by summing L&R, perhaps using a simple mono output 3.5mm jack (https://cpc.farnell.com/pro-signal/psg08686/3-5mm-jack-plug-mono-gold-black/dp/CN21230 ), but I see that might not be the best.

Most intercoms have some way to include an aux input of some sort, traditionally to feed in marker tones (not that there are many of those around) or similar. 
The SPA-400 involves adding a resistor, then linking it into the headphone output
https://www.sigtronics.com/air/spa.html
https://www.sigtronics.com/_pdf/air_pdf/air_intercom_pdf/SPA-400_AUX_Audio_Input_Inst.pdf
https://www.sigtronics.com/_pdf/air_pdf/air_intercom_pdf/ICS-Load_1440_Mod.pdf

The Trig Compact COMs have, like most modern radios, a built in Aux input:
https://www.trig-avionics.com/product/compact-radio/
https://www.trig-avionics.com/library/00839-00-AG%20TY9x%20Installation%20Manual.pdf (search for Aux)

I'm unsure whether the audio output from the Pi will be strong enough for the two headsets that we have wired in via the SPA-400 and unsure of the resister value required to add to link it into that system to allow the intercom to still work.  I was hoping that someone may have already tried it.
I'm more confident that input via the Trig will just work.

Adding a muting facility is important to us as both aircraft are used for circuit work and training from time to time.  I don't want continuous bearingless information for someone taxiing around an airport outputting Mode-C while we are doing circuits under ATC control, yet bearingless is going to be important in the areas we normally operate in as a lookout reminder as I don't think there are enough ground stations for consistent multi-lateration (based at Prestwick).  An external volume control, to me, is better than an on/off toggle.

I want an on/off switch as PAW will be installed behind the panel in each aircraft. I expect it will be kept off until engine has been started (we don't have separate avionics buses) to protect it and ensure max power is available for engine start (I know that modern avionics are designed to handle the power fluctuations during start but I suspect a Pi hasn't been?). A single knob seems a sensible way to do this and describe to the other large number of group members.  I assume there isn't an audio annunciation that PAW is up and running?  Could that be added as an enhancement so a pilot knows the system is working?  A number of our group rarely use tablets (airspace isn't as congested up here!) so their only PAW interaction will be via audio.

AlanG

Re: Wired Audio PAW to Intercom volume control
« Reply #6 on: November 05, 2020, 08:57:40 pm »

Hi Riverrock

It is an extremely good idea to have a separate power switch in line for the PAW.  If only using the a/c master switch, it can be part way through its boot procedure as the starter is operated and this draws away power and interrupts the boot up.  This can happen several times if you turn the engine over on the starter.  Once boot up is complete there is an annunciation of "Pilotaware" that will come through the Bluetooth Audio and the Audio jack and via this to your headset once connected by your chosen method.  I personally use one of the Hart Mixers mentioned in a previous post.  This gives me two channels fully adjustable independantly and a master volume that can be used to wuiet the calls if required.  It means I can have Paw Audio or my EFB audio or both.

Regards
Alan


riverrock

Re: Wired Audio PAW to Intercom volume control
« Reply #7 on: November 05, 2020, 10:01:29 pm »
Quote
Once boot up is complete there is an annunciation of "Pilotaware"

Thanks!

exfirepro

Re: Wired Audio PAW to Intercom volume control
« Reply #8 on: November 05, 2020, 10:42:05 pm »

Adding a muting facility is important to us as both aircraft are used for circuit work and training from time to time.  I don't want continuous bearingless information for someone taxiing around an airport outputting Mode-C while we are doing circuits under ATC control, yet bearingless is going to be important in the areas we normally operate in as a lookout reminder as I don't think there are enough ground stations for consistent multi-lateration (based at Prestwick).  An external volume control, to me, is better than an on/off toggle.

I want an on/off switch as PAW will be installed behind the panel in each aircraft. I expect it will be kept off until engine has been started (we don't have separate avionics buses) to protect it and ensure max power is available for engine start (I know that modern avionics are designed to handle the power fluctuations during start but I suspect a Pi hasn't been?). A single knob seems a sensible way to do this and describe to the other large number of group members.  I assume there isn't an audio annunciation that PAW is up and running?  Could that be added as an enhancement so a pilot knows the system is working?  A number of our group rarely use tablets (airspace isn't as congested up here!) so their only PAW interaction will be via audio.

Hi again riverrock,

All understood. AlanG and I both fly flexwings out of East Fortune and live in West Edinburgh, by the way. We have both been heavily involved with the development of PilotAware since it started back in 2015, and run several PAW ATOM GRID Ground Rebroadcast Stations through in the East.

I’m pleased to say there are also now Rebroadcast Stations through in the West, at Lenzie, Strathaven and a new one has recently been set up just south of Tarbolton, which is already providing excellent cover over Prestwick and the Kilmarnock Corridor, and to the south west out towards the Antrim Coast. It will be even better once the owner gets the antennas outside onto his chimney! I have also just been advised that another station will soon be installed (by one of your Club Members?) at Coylton, which should considerably improve both MLAT coverage and reliability around Prestwick.

Alan and I also have excellent contacts withTrig, BTW if you need any help there.

If I can be of any further assistance, please feel free to drop me a P.M. via the Message Board.

Best Regards

Peter

steveu

Re: Wired Audio PAW to Intercom volume control
« Reply #9 on: November 05, 2020, 11:49:34 pm »
Just some additional info - not contradicting anything already said.

Microavionics intercoms in use in microlights have a couple of 3.5mm Aux in jacks, so a 3.5mm to 3.5mm lead will sort you out, no soldering.

I have tested this out and it works, audio levels are good.

They also have a Bluetooth input.

Lynx is a bit more fussy, you need a 3.5mm to Binder type multipin bayonet connector.

Microavionics manual claims that in the even of incoming audio from the radio, the Aux input gets muted.

This could be a huge bonus.

I didn't wire a pot into the PAW I helped install in the flex I have access to, but I'm going to in the Skyranger I partly own. That has a Lynx interface with no alleged auto mute, so a mixer with input levels, to balance audio and an output level to instantly mute everything will be chosen.

 

AlanG

Re: Wired Audio PAW to Intercom volume control
« Reply #10 on: November 06, 2020, 08:19:44 pm »

Hi Riverrock

I see from your opening post that one of the setups you are working on has the Trig radio utilising the built in intercom.
This system does allow for an Aux input that is auto muted when radio transmissions received or sent.

Alan

riverrock

Re: Wired Audio PAW to Intercom volume control
« Reply #11 on: November 06, 2020, 11:32:26 pm »
Indeed it does (the other aircraft I'm looking at doesn't) but from what I hear from others, distraction is the issue which would need addressed with the ability to turn off audio.
In our part of the world, distraction is a bigger risk than a collision.