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#msg6959The 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#msg16904If 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