[TRLog] sbdvp III

Kenneth Earl Harker kharker@cs.utexas.edu
Wed, 22 Apr 1998 02:10:35 -0500 (CDT)

   OK, I'm getting closer.  I now have the PTT line working (TR and SBDVP 
both think my one and only printer port is LPT2, whereas MS DSP, the one 
program I've used the printer port with before now still thinks it is LPT1.)

     I think the playback might work, although I've not found anyone to listen
to the audio yet to tell me if it's OK.  I definitely do not have the recording
working, nor does the cabling I have now let me talk through to the radio as 

   The following (as I see it) is the challenge:

Microphone  --------------\/-- B -------------- Soundblaster Mic in  


     Radio  --------------/\-- C -------------- Soundblaster Line out

SBDVP provides two signals on the printer port, one during recording, and 
one during playback.

Recording   Playback      A      B       C
    0          0       Closed   Open    Open
    1          0        Open   Closed   Open
    0          1        Open    Open   Closed
    1          1       We're in trouble here!

I've thought about how to do this with 2N2222A's, but frankly it's making my 
head swim, and my first attempt at building it has failed.

I'm looking at some of the CMOS Analog Switches in 16-pin DIP packaging in
my TechAmerica catalog (i.e. September '97 catalog, pp. 131 and 132) in hopes
that this might simplify things.  Keep in mind, I'm not an engineer :-)

For the technical folks:
   When I look at these pinouts, I see the IN1, S1, and D1.  Presumably, this
means that when IN1 is raised to positive voltage, the switch between S1 and D1
is opened (or closed as the case may be.)  There are also pins GND, V+, and V-.
I understand GND, but what would I need to be connecting to V+ and V-?  +5V
and -5V?  All the time?  Is there a way to easily get this from the printer
port using TR?

    It looks like for the above, all I'd need is two of these quad packages, 
one normally open (for B and C), and one normally closed (for A), and I guess 
an OR gate in front of A.  What are the odds this will all fit inside a 
DB-25 shell? :-}

    Finally, assuming that all the above works, how do I tell if the microphone
is a good match for the sound card mic input?  What do I need to know about
impedances and such?

    Am I overlooking anything?

    Besides the value of a W9XT contest card? :-)

Kenneth E. Harker      "Vox Clamantis in Deserto"      kharker@cs.utexas.edu
University of Texas at Austin                  Amateur Radio Callsign: KM5FA
Department of the Computer Sciences         President, UT Amateur Radio Club
Taylor Hall TAY 2.124               Maintainer of the Linux Laptop Home Page
Austin, TX 78712-1188 USA            http://www.cs.utexas.edu/users/kharker/

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