On Wednesday 18 September 2019 22:39:23 John Hasler wrote: > Joe writes: > > What would be a real pain is actually accessing HDMI signals while > > the thing is running. It's no good just looking into a connector, it > > needs to see something hanging on the end before it will power up > > and activate. > > Well of course he'd have to build a breakout box. Trickier than RS232 > but straightforward enough as long as you know how to deal with UHF > and impedance matching as Gene clearly does. > > An rf voltmeter would suffice to determine if the lines are waggling.
Maybe, but I've been looking at a scope with a probe in one hand since 1951, and my eyes can make sense, see an error and recognize it as such, sometimes before the circuit actually mis-behaves. Such single ended circuits have a worst enemy, I call it ground bounce, and it can totally destroy a single ended circuits signal integrity, or even blow chips if brutal enough. But I also understand that hdmi is low voltage differential, and I'm not as well eyeball trained on those. But I can always recognize an echo if the scope is fast enough. Sometimes you have to do a bit of math (my poor suite because in actual fact my formal education is to the 8th grade only) to confirm the distortion you see is an echo though that gets difficult when the cable is well under a foot long and the echo's fundamentel delay is closing in on the scopes bandwidth. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene>
