[vdr] Re: How to connect the SPDIF of the DVB-s rev 1.3 to a standard SPDIF?

["Reinhard Walter Buchner" <rw.buchner@freenet.de>]

Hi Ulrich,

> will this also work with the rev. 2.1 dvb? or do
>they have completly f**ked up that revision?
> 
> Thanks & Cu Ulrich

The rev 2.1 doesn't have the J2 pinconnector. However
(I don't own one), as far as I know they have a SPDIF coax
output on the included (cable)whip.

It should be possible to connect the TOTX in a similar
fashion, but you will need to add a bit of electronics:

                                   +----10K--+                       
                      10 nF        |         |
                       ||          |    |\   |        |\
Rev 2.1 ouput -----+---||----100R--+----| O--+---+----| O----- TTL out
                   |   ||               |/       |    |/
                  75R                           10K
                   |                 74HCU04     |
                  ---                           ---
I hope this comes out right, darn Ascii art. Just in
case it doesn't, here is a small description.

- the 75 ohm are parallel to the SPDIF output
  this terminates the output of the DVB and prevents
  reflections on the line (similar to a LAN terminator)
- the hot end goes into the 10nF DC blocking cap

- the other lead of the cap connects to a 100ohm resistor

- the other lead of the resistor enters the hex inverter

- the 10k "cheater resistor" goes from the input
  to the output of the hex inverter (i.e. across it)

- from the output of the first inverter to ground is a 10k
   resistor to load the inverter & prevent false triggering
   info from reaching the second inverter.

- the last inverter re-inverts the signal (so that it is back
  in phase with the input signal)

All this circuit does it transform the standard HiFi SPDIF
output into the necessary TTL signal level, which is needed
for the TOTX. The coding format of the signal is the same
for coax & optical. Only the signal levels are different.

Now you can feed the output of the second inverter into
your TOTX and it should work as it would with a DVB
card having the J2 connector.

Of course you will need to steal 5V and a few mA from
somewhere (PC PSU) for the inverters and the TOTX
Not in the schematic, but also necessary Pin 7 of the
Hex inverter goes to ground and pin 14 goes to Vcc
(+5V). Let me know if it works. The circuit is quickly
built on a small strip of breadboard.

Greetz,
Reinhard



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