High Low Radio

[weirdjim]

It has been a LONG time since I've done a radio install and I can't remember the convention.

There are several input/output pins on the Garmin I'm helping install and they go something like:

Headphone output HIGH
Headphone output LOW

Aux audio input HIGH
Aux audio input LOW

...and so forth.

Are they actually two separate inputs or outputs, one high level and one low level or is "LOW" simply another word for a separate audio ground for that particular function?

Thanks,

Jim

 

[bnt83]

LO = audio ground/return
HI = audio positive/+

Top picture, the PMA8000BT does not have an input for the com mic return so that wire is grounded at the audio panel. (the ground symbol missing at the shields in that pict BTW)

 

[PW_Plack]

The common is often called called "low" or "-" in devices where multiple ground connections would cause a ground loop. In such circuits, there is usually only one ground specified, and adding more can cause gremlins.

Some mobile devices should not have their 12 VDC power grounds connected to their audio grounds.

Some of these "floating" circuits may require mounting the mic and headphone jacks in plastic, or use of a special jack with an insulated shoulder washer to prevent contact with the panel in which they're mounted.

 

[bluerooster]

Yep, pretty much the short and dirty: High= + Low= -
And try to refrain from using a "common ground" as is done with some car radios.