Comments on: DIY A/V switch

By: Randy

Randy — Mon, 26 Mar 2007 13:40:18 +0000

Yes..this is just the way that everybody want

By: Jona

Jona — Thu, 15 Mar 2007 18:57:46 +0000

why not switch them with some HF reed-switches or something..

By: DJ-Q

DJ-Q — Thu, 15 Mar 2007 11:52:44 +0000

It would be neat to incorporate a HD44780 screen into this project and display a friendly name of the device that is active i.e PS3, DVD, XBOX etc

Also surely IR control would be an easy addition to this.

By: hnch

hnch — Thu, 15 Mar 2007 10:15:12 +0000

well “…”, have you had a look at the internals of the chip in the data sheet? the chip only contains so-called “transmission gates” (you might want to google that term), not that different from what a CD4066 does (except for the lower ‘on’ resistance). i had built an audio crossbar switch with CD4052s when i was a teenager and it worked quite well. but i wouldn’t attempt to switch composite video (6 MHz of bandwidth!) with such a chip that has undefined input and output impedances. and a wrong termination can be quite ugly at these frequencies (ghost pictures). Not even speaking of VGA or even DVI/HDMI, that’s mere RF voodoo. Analog Devices has some fine chips for such purposes – but those need a proper pcb layout.

By: ...

... — Thu, 15 Mar 2007 03:06:26 +0000

ya um guys, that chip is defantly not designed for analog video switching... Those pins are designed for pure digital 0 or 5v signals, and likewise have absolutley no quality control on them, they just need to be able to keep the signal within ttl spec... You got lucky that the signal didn't get converted to a ttl signal by sending it through the chip.

If you are going to go to the effort to make a big howto on a project like that, at least use a chip designed for the application, ok?

What you did is sorta like using a lm317 variable voltage regulator as a high power op amp, sure it will sorta work but the signal is going to be crap.

By: twistedsymphony

twistedsymphony — Thu, 15 Mar 2007 01:54:35 +0000

it’s a neat project (not a hack… more of a diy) and haveing built one of these before myself (complete with IR control) I can whole heartedly agree with akmixdown, why use a a more expensive digital chip to do a less expensive analog chips job?

In terms of AV switches quality is the second most important factor…(directly behind ease of use, else you’d be switching em by hand :P )

By: Wolf

Wolf — Thu, 15 Mar 2007 01:49:23 +0000

looks, usefull, if the quality is good, hopefully ill be able to stop manually switching my monitor cable between my comp and 360, i’ve tried kvm switches, but nothing under $50 has given me an unghosted image…

By: computerguru365

computerguru365 — Thu, 15 Mar 2007 00:54:57 +0000

i did this using a old printer a/b switch - took a while to figure out, but it is well worth it. i use mine all the time - http://computerguru365.blogspot.com/2006/02/diy-rca-switch-box-updated.html

By: akmixdown

akmixdown — Thu, 15 Mar 2007 00:16:48 +0000

I just checked out the datasheet on these things... they're not really meant to switch analogue signals at all. While this may work, you're operating these devices in an unintended operation mode and results may vary from batch to batch. I realize that we're all hackers here or perhaps only wannabe hackers living vicariously through people like benheck, but it's just something to be aware of.

If you really wanted to do this, why not use something like Maxim, National, Analog's or really *anyone*'s A/V switch chips? Using a high-speed LV244-equivalent doesn't really seem like such a hot idea, when you can get the same (and likely better) performance out of a cheaper chip designed for the purpose.

As far as SMT goes -- there are 74LV/HC/ACT244s available in DIP form, too... :-)

By: Nathan

Nathan — Wed, 14 Mar 2007 22:09:09 +0000

i’ve wired component through the triple a/v RCA connectors to look fine

By: Craig Younkins

Craig Younkins — Wed, 14 Mar 2007 21:49:45 +0000

I want a DIY DVI KVM (hooray for acronyms!)

By: pragma

pragma — Wed, 14 Mar 2007 21:41:55 +0000

Nice. But of course it wouldn't be a BenHeck tutorial without a complete spaghetti bowl wiring setup in the end. I wouldn't want to put together more than 3 A/V inputs using this technique.

That said, I know that making a PCB was well outside the scope of this one, but I'd love to see how that would reduce the space and complexity for higher numbers of inputs.

By: conor

conor — Wed, 14 Mar 2007 21:31:41 +0000

could this be used for a simple KVM switch?

By: Oracle

Oracle — Wed, 14 Mar 2007 21:21:04 +0000

This is a very cool project, but why are you referring to it as a “trick”? This is exactly the sort of things the bus chips are meant for. It’s like saying (in 2007) that running a web browser on your PC is a really cool hack and Mac’s are your thing, you can probably use the same trick there.

By: thijs

thijs — Wed, 14 Mar 2007 20:32:00 +0000

no, read the article..
it's composite video + 2 audio channels.

nice hack!