Push to talk wiring

[markejackson02]

Scratching my head.

Wanted to install a PTT switch on the co-pilot yoke.  I see the wire (on the pilot side) goes from the microphone jack connection to the PTT switch and then to the intercom DB-9 connector.  So I assumed pushing (closing) the PTT switch causes the intercom to channel the audio from the mike to the appropriate radio.

How come if I put a hand held mike in the same jack, and press the transmit key, it transmits?  The PTT switch is open in that case and I don't see how the audio is sent to the radio.

Forgive my rudimentary understanding of electronics.

Edited April 1, 2017 by markejackson02
clarity

[Hank]

Connect the right wires to the right terminals, and keep the smoke inside. That's my total knowledge of electronics. I'd look at mine for you, but it's 400 nm away right now 

[N601RX]

The ptt is soldered across the tip and barrel terminals of the mic connector.  The audio is then carried on the ring terminal. The tip and barrel is the ptt signal and mic low on newer stuff but is just ground on some of the really old stuff that doesn't have a separate return path.  

Essentially your handheld mic has its own switch which is connected in parallel to your ppt button.

Edited April 1, 2017 by N601RX

[carusoam]

There is also some logic to what works when in the event of some systemic failure...

Finding a wiring diagram for the audio panel will be very helpful...

When the intercom is a separate device, the wiring diagram gets slightly more complex.

What audio panel do you have?

What intercom do you have?

See if we can find these docs on line...

Best regards,

-a-

[kerry]

You need to find a wiring schematic to your intercom.  It should be as simple as finding the correct wire(co-pilot PTT) from the intercom and hook it up to a PTT switch and the other side of the PTT goes to ground.  On the your pilot side the wire probably goes through the mike jack so you can use a hand mike or a portable PTT button.  I have a Sigtronics SPA400 and this is my schematic.  https://www.sigtronics.com/_pdf/air_pdf/air_intercom_pdf/SPA-400_Narco-COM810_Inst.pdf  

[Yetti]

5 hours ago, markejackson02 said:

 So I assumed pushing (closing) the PTT switch causes the intercom to channel the audio from the mike to the appropriate radio.

Nope.  The audio panel selects where the mike and audio come and go from.  PTT is from the Pin on the audio panel to the switch to ground. 

[markejackson02]

Right now I have an old Sigtronics/King system but it is being replaced by a PMA450 from PS Engineering soon.  Very interesting.  The PTT switches in that wiring schematic are wired from the Pilot Mic Lo (ring connector) to the Pilot Mic PTT (tip connector) while the barrel connector carries the audio.  Pressing the PTT closes a circuit that connects those two wires which I assume tells the PMA to transmit.  So I can see how a hand held mike would work in that case.

[N601RX]

Mic low should be to the barrel not the ring. Ring carries the audio

Edited April 1, 2017 by N601RX