> I wish to build a device that will send an ID down a cable (twisted
> pair) and be picked up at the far end in order that the cable can be
> identified. Now I already use a tone and amplifier which will send a
> audio frequency tone down a wire and be picked up at the far end, using
> a commercial "Tone/Amp" set from Progressive.
>
> What I what is to be able to attach a series of "tones" or voice ID's to
> one end of say a 30 pair telecoms cable and read off which cable is
> which at the far side without having to physically switch the device
> from one pair to the next, ID'ing say 10-20 pairs at a time.
>
> There is a commercial unit that does what I want called the Voice IDer
> from Tempo at
> http://www.tempo.textron.com/products/prod_voicetaggers.html
>
> and http://www.tempo.textron.com/archive/ds_voicetaggers.pdf
>
> I want to build this type of device using a PIC ??? although I am
> totally new to PICs and their capabilities.
>
> OK now the question. Can anyone help out with a design/circuit or any
> ideas as to how it could be designed built programmed?

I'm sure there are lots of ways to do this.

The brute force solution would be to drive each twisted pair with a
different audio signal of a voice saying "one", "two", "three", etc.  That
would make the transmitter complicated but the receiver just a simple
audio pickup with a small speaker.

However, I can think of simpler ways to accomplish the overall task.  I
would send different digital signals down each pair.  These "digital"
signals would be drived from PIC output pins, but with a little low pass
filtering applied to reduce crosstalk.  I'm thinking maybe a manchester
data stream with a 100Hz bit rate, low pass filtered to 3KHz.  (I'm making
up these numbers on the fly.  The numbers may not be optimal, but I think
the concept is sound.)  The idea is to keep all the information within the
typical voice bandwidth.  That's why manchester encoding is attractive,
since it has no frequency components below the bit rate.  Manchester
signals are also self clocking and easy to generate and receive with a
PIC.

The receiver would require a little analog circuitry to reconstruct the
original digital signal, protect from spikes and transients, tolerate wide
variation in amplitude, etc.  The PIC would decode the data stream to
determine the 5 bit line ID.  They you can do a lot of different things to
notify the user of the result.  A simple answer would be some kind of
morse code like output.  However, it should be possible to play a short
audio segment every second or so selected by the line ID.  These could be
stored in an external EEPROM and written to the PWM output, then low pass
filtered and amplified to drive a small speaker.


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