Disclaimer:-
You take this information and use it ENTIRELY at your own risk.
I and this site hold no responsibility for any errors either in this text or with your electronics capabilities...
The reason I have given this away is/was because I needed an audio input for a simple MacBook Pro
Python Audio-Oscilloscope I am developing.
(This is also shown in a different guise at the end of the AudioScope shell script too.)
BEST VIEWED IN PLAIN TEXT!
Machine:- Apple MacBook Pro 13 inch.
OSX 10.7.5...
Vintage:- August 2012.
Common 3.5mm, 4 pole, Mic/Ear socket cable for external MONO audio input, (and
stereo audio output)...
Plug required, (or similar)...
http://www.ebay.co.uk/itm/3-5mm-Mini-Jack-Right-Angle-90-Degree-Solder-4-Pole-Male-Plug-Connector-/320770305756
Resistor, 2K2, 1/8 W, 10% tolerance...
(2 x Resistors, 33R, 1/8W 10% tolerance...)
This is the wiring for the auto-switching of the Mic input to external...
Pins. Wiring.
----- TIP -------
1 ----> O <----- Left Audio Output +ve.
2 ----> H <----- Right Audio Output +ve.
3 ----> H <----- Mono (Mic) Input, Active.
4 ----> H <----- Common To All Inputs And Outputs.
---
| |
| |______
|__________|=========
For the auto-switching capability a 2K2 resistor must be connected across Pins 3 and 4. [Mono (Mic) Input, Active and Common]...
Test by plugging into the socket and check that the "System Preferences > Sound" switches over to external input and output.
You now have two audio outputs at low impedance and an analogue audio input at around 2K2 _impedance_.
Do NOT drive the input with more than 100mV AC and do NOT connect to a DC _supply_ either.
Do NOT load the audio outputs with less than 33 Ohm resistors.
Do NOT assume that Common is connected to GND, Ground, of the computer, although it may well be.
I am assuming that if you are capable of doing this that you are also capable of doing the subtle level tests etc...
(C)2012, B.Walker, G0LCU. (Issued as Public Domain for all.)
Enjoy finding simple solutions to often very difficult problems... ;o)