[sdiy] DIN Sync voltage thresholds? Digital signalling over normal audio cables?

[rburnett at richieburnett.co.uk]

> 1. what are the usual voltage thresholds below which a sync pulse
> gets > rejected as noise? I understand this is a broad question
> since din sync is just a clock in a pulse train, however I'm
> hoping for rough figures at least..

You need about 0.6V to turn on a transistor, so anything less than this 
is probably a safe bet.

> 2. has anyone tried doing "fast" digital signalling over the
> following cables and what were good reliable speeds you could
> get on them?

It doesn't matter as much about the type of connector as the overall 
continuity of the entire link.  You can easily achieve tens of kbits/s 
over any of the connectors you mentioned if distances are limited to a 
few metres.  Speeds up to tens of Mbits/s and beyond are possible over 
simple twisted-pair cable provided it's good quality cable and it is 
correctly terminated at each end (think USB or Ethernet cables.)  The 
thing thats most important is impedance matching so that you don't get 
waveform distortion and reflections back from the ends of the cable.  
That's why, for example, video equipment has a 75 ohm impedance at its 
output, 75 ohm cable, all connectors have 75 ohm characteristic 
impedance, and the input impedance of the monitor is also 75 ohms too.  
This ensures that high frequency signals are conveyed without incurring 
reflections from any discontinuities in the link.

-Richie,