No 1 to 4 AV selector?

October 24, 2007 7:30 PM

Why won't an AV selector work backwards?

I have a few of those AV selectors from Radio Shack, funneling various components into one output. Why won't they work in the opposite direction? 1 input to 4 switchable outputs?

posted by minkll to technology (8 comments total)

They should. Can you give us a more detailed explanation why they actually don't?
posted by suedehead at 7:32 PM on October 24, 2007

If it's a mechanical switch, it should work. An electronic switch wouldn't.
posted by kindall at 7:38 PM on October 24, 2007

Is it one of the switches that have the mechanical buttons or does it have a remote/other buttons?
If it has mechanical buttons then it ought to work.
posted by ooklala at 7:41 PM on October 24, 2007

It should work, and I've used them this way for audio (the mechanical-switch ones). If it's electronic, it might not work depending on how the circuitry is designed, but if I had to make a bet I'd say it probably would.
posted by Kadin2048 at 7:44 PM on October 24, 2007

Hmm. They're mechanical switches, but responses seem to indicate I did something wrong. I'll try it again.
posted by minkll at 7:59 PM on October 24, 2007

They might have built diodes into it to protect your components from each others' signals, thus preventing you from using it backwards as a side effect.
posted by mmoncur at 8:37 PM on October 24, 2007

mmoncur: Both audio and video signals cross the 0V axis, so a diode wouldn't work. It would chop the signal in half (passing only the positive or negative portion of it), not act as a 'one-way valve.'

For that to work you'd have to apply a DC bias to the signal for it to pass through the diode, which is possible but unlikely.

I'm trying to think of other reasons why it would be, but coming up blank. In general, it's actually quite difficult to produce a "one way valve" for AC-biased signals like audio and video.
posted by Kadin2048 at 11:11 PM on October 24, 2007

What kind of connectors are on this switch?

If they're Composite Video+Stereo Audio over SCART connectors, then Video/Audio IN and Video/Audio OUT use different pins - so the switch would only forward IN signals. Invert the switch to give 1-in/4-out wouldn't change the pins and hence you'd get "outgoing" signal on the IN pins of the four "outputs", and hence no visible/audible output signal.
posted by Nice Guy Mike at 11:58 PM on October 24, 2007