RE: SCART switching with Homevision

["Steve Morgan" <steve@xxxxxxx>]

Eee, Keith, you lovely man!

I knew you'd have the answer. I reckon I can keep all of my 4x3 sources
on one AV input using the Quattro+ and the other two for Sky and DVD, so
I should be able to hard wire (or jumper) the 12v/5v supplies.

Cheers,
Steve

> -----Original Message-----
> From: Keith Doxey [mailto:ukha@xxxxxxx]
> Hi Steve,
> +12 will select a SCART and +5V will select widescreen mode on a
> +compatable
> TV.
> To get Homevision to do the switching you need to use Port A
> Wire a 1K resistor from a +12V supply to a pin of Port A,
> (open collector
> output) and wire the Port A pin to pin 8 of the SCART,
> connect the 0V of the power supply to one of the ground pins
> on the SCART. When the Port A is low it will short the SCART
> end of the resistor to ground and the TV will not be
> "grabbed" when Port A is high (open circuit) the 12V supply
> will feed through the resistor to the SCART and grab the TV.
>
> If you want to be able to select widescreen mode as well you
> will need two pins on Port A and a couple of diodes as well.
>
> Poor attempt at a diagram follows
>
> +12V ----- 1K Resistor ---------------SCART Pin 8
>                                 l
>                                 l
>                             Port A pin
>
>
> For the 12V/5V switching it is like this
>
> +12V ----- 1K Resistor ------------Diode>-----
>                              l                l
>                              l                l
>                          Port A pin 1         l-----SCART Pin8
>                                               l
> + 5V ----- 1K Resistor ------------Diode>-----l
>                              l
>                              l
>                          Port A pin 2
>
> The diodes prevent the two voltages being shorted by the
> other Port A pin, it doesnt matter if both are output at the
> same time as the 12V will take precendence and grab the TV in
> full screen mode.
>
> Hope that makes sense :-)
>
> Keith


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