Comments on: No 1 to 4 AV selector?

Question: No 1 to 4 AV selector?

minkll — Wed, 24 Oct 2007 19:30:37 -0800

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?

By: suedehead

suedehead — Wed, 24 Oct 2007 19:32:41 -0800

They should. Can you give us a more detailed explanation why they actually don't?

By: kindall

kindall — Wed, 24 Oct 2007 19:38:01 -0800

If it's a mechanical switch, it should work. An electronic switch wouldn't.

By: ooklala

ooklala — Wed, 24 Oct 2007 19:41:49 -0800

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.

By: Kadin2048

Kadin2048 — Wed, 24 Oct 2007 19:44:05 -0800

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.

By: minkll

minkll — Wed, 24 Oct 2007 19:59:15 -0800

Hmm. They're mechanical switches, but responses seem to indicate I did something wrong. I'll try it again.

By: mmoncur

mmoncur — Wed, 24 Oct 2007 20:37:47 -0800

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.

By: Kadin2048

Kadin2048 — Wed, 24 Oct 2007 23:11:35 -0800

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.

By: Nice Guy Mike

Nice Guy Mike — Wed, 24 Oct 2007 23:58:58 -0800

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.