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

cheater00 . cheater00 at gmail.com
Wed Jul 10 15:54:34 CEST 2013


Hi Richie,

Thanks a lot for your reply. I had thought the world had all but given
up on this thread!


On Wed, Jul 10, 2013 at 3:29 PM,  <rburnett at richieburnett.co.uk> wrote:
>> 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.

Hmm, are you saying all / most designs just feed directly into
transistors working in switch mode, without any level shifting etc?

>> 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,

Yeah, impedance matching is important - but I'm guessing those cables
can't really be in an impedance-matched design. Plus, I'd still want
to be able to 1. feed legacy equipment with such a signal coming from
an "enhanced" unit 2. consume signals from legacy equipment going to
an "enhanced" unit. So now the question is, if one end is impedance
matched, and the other not, what happens. I'll have to think about it,
but I'm guessing depending on whether the impedance mismatch is at the
receiver or at the sender I'll just get mirroring at different times.

D.


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