Hi all,
Having few devices, which can produce alerting sounds (O2D2 system, iPad, etc) I need solution to mix them to single line-in in my 172. Y-cable is not solution in this case (only for spliting output). Can someone recommend any compact device powered by USB or batteries to use?
Perhaps this ?
There’s a few alternatives at spruce, too. Available elsewhere, too, of course.
Normally, one can get a good enough result just by bringing in all the sources via 560 ohm resistors, and the join of all the resistors is the output.
That is how one deals with e.g. bringing TCAS, GPWS and autopilot warnings all into a single unswitched intercom input.
On my plane, the EASA145 EASA 21 etc etc shop which installed my TCAS did this by wiring them all together, without resistors, and the lowest output impedance source won the day while the others didn’t do anything 
…and poor me who considered an opamp mixer, for a total component cost of 10 quid or so. Well, say 15, if one counts a custom designed PC produced in small numbers. Or perhaps 25, if using gold-plated connectors. I really missed my career, obviously.
Then again, even your resistor solution would require the use of certified individually tested aviation grade resistors, I reckon, if the concoction is to be installed permanently?
I think, I have to clarify :) I have one 3.5mm “jack” line-in below trim wheel. I need a small box, that would be able to mix signal from 2-3 devices with the same 3.5mm outputs. Offcourse, it can be RCA or anything else – it’s possible to find adapter on the market. So it’s intended to be used in cockpit, not to be mounted somewhere inside the panel.
If making own circuit, than I presume, that diodes are also required?
But, better, offcourse to get turnkey solution :)))
Noooo, you heatshrink-sleeve them and hide them in the wiring harness
No diodes; you are mixing audio signals, not logic etc levels.
Of course the proper way is to make a proper mixer (an op-amp, virtual earth, etc) but then you need to power it. The resistors should give you a quick and dirty solution.
If at that point the signal is stereo, you will need to do this for each channel separately.
The beauty of the resistor solution in your application is that it does not need any power, which given that you probably already looking at a cat’s cradle of wires and hoses, would be a major advantage. As long as you don’t need HiFi quality, it will do the job of getting the warnings connected to where you need them.
@Peter: I have to agree, heatshrink-sleeve is a wonderful way to make an electric/electronic “bricolage” more or less mechanically stable AND quite unconspicuous. A bit the electronic equivalent of duct tape. Think I’ll shortly be investing in several metres of the stuff, in various colors and sizes.
@pshz: here’s an offer for you. I’ll implement Peter’s idea in a neat plastic box (or as a heatshrink-sleeved “incognito”, if you prefer) with output and inputs as per your requirements. All 3,5 mm, I presume? As a free gift! You just need to come and pick it up at or near my home field on your trip to Croatia, or on your way back home. If it must be stereo, you’ll owe me a beer, though.
Thank you, Jan. I’ll try to do myself ) Fortunetely, I have few 560 ohm resistors )))
Sounds like at least half of the forumites here have a soldering iron ready and smoking. If we had member polls, that would be a good subject.
But frankly, pshz, do you really think your excuse good enough for not having a beer together, one day?
