I appreciate the suggestions I have heard, so far.  It
does sound like I need a FIFO.  Actually, if I need to use
several logic IC's, I may already have what I need.  I was just
checking to see if there was a lazy-man's solution.

        There was going to be a PIC involved, anyway, but it may
end up taking a more active role in handling the bit stream.

        I already have a 8-KB RAM chip and I believe I also have
a suitable counter which could be used to address the 13 address
lines on the RAM.  The idea would be to use a PIC like a 16C54 to
handle the stepping of the counter, the reading from and writing
to the RAM, and the serial clocking in and out of the bits.

        One of the neat things is that since the RAM will always
be read and written as a circular queue, a simple counter can do
this.  Also, if one reads first, then writes, you get the delay.
The PIC could even throw away the first 8-KB cycle after power up
as there will be nothing but garbage in the RAM.

        I initially thought about a 16F84 which would work, but
there aren't enough pins to do everything I need to do.  All of
PORTB would be the I/O bus for the RAM.  The five pins of PORTA
would be taken by the clock pin for the address counter, Data in,
Data out, Bit clock in and maybe Bit clock out.  I wanted to do
some other things, also and that would use up all the I/O pins on
the PIC.

        The CODEC I am using needs a 1.024 MHZ clock crystal or
suitable external clock so I figure I can try to find a 4.196,
8.192, or 16.384 MHZ crystal for the PIC and use another counter
to divide it down.

        All that should give me the 1-second audio delay plus the
ability to monitor the bit stream and detect signals.  It is
totally amazing how this project has metamorphosed over the last
year and I haven't even done any serious construction yet.  I
truly appreciate the problems engineers must have who are
fighting deadlines and company costs while still getting things
done.  This is just a fun project for me that I may also write an
article about when done, but I would have been put out on the
street if I was doing it for a living.

        I have been building VOX or Voice Operated Relay (X short
for relay) switches for over 20 years and it is now becoming
practical to use digital audio for the delay to give the tape
motor time to get up to speed and the capacitors in the audio
circuits time to charge and so forth.

        The holy grail will be to use a Smart Media card to store
minutes of audio rather than depend upon the tape drive to stop
and start for each sound.  For now, the 1-second delay will be
good enough.

Martin McCormick WB5AGZ  Stillwater, OK
OSU Center for Computing and Information Services Data Communications Group