image output is skewed keystone issue.

[james]

I can tell the difference right away between a laptop with a floating ground power supply and a desktop with a three prong plug if either is using a USB sound device as a signal source into my projector (which has a 3 prong plug).

[dchammonds]

I can tell the difference right away between a laptop with a floating ground power supply and a desktop with a three prong plug if either is using a USB sound device as a signal source into my projector (which has a 3 prong plug).

I've run into the same issue when connecting a soundcard from a desktop computer to a full size audio rig. You want one and only
point where the common side of the audio card meets the amp- any other paths to earth ground or the computer chassis can cause trouble.

[dchammonds]

Yes. I stay up too late most of the time.

I've heard about other people using sound devices that rely on playing a constant negative (digital) signal to pull the DC offset down to near zero to keep the lasers off. That sounds like a recipe for disaster to me.


.

Seriously??????

[prosnurfer]

hey everyone! got pulled away from my trouble shooting the last few weeks with work, skiing and subaru engine gaskets but thanks for all your replies. just checked my emails when i got home from work this morning and omg! reading all the grounding comments I was like well i have a common ground but then the laptop comment from James... the one thing that was different when i fired up my projector was i was using a crappy hp laptop in my dining room to play around. back in vt i had all my music mixers and electronic projects always run off my desktop pc. i was like no way i have to check really quick. sure enough the dumb hp laptop (never buy one i had to for work emails on a vacation) is the cause of the signal issue. plugged in to my desktop the skew is resolved and i can properly align optics. cant belive such a silly thing.

do any of you have problems running off laptops ever? maybe a cheap power supply?

anyways thanks so much for all the help, After the move I have been using my pc on my living room tv and still have yet to set up my work room, didnt want to run my projector in my living room too many windows for beams to escape, and I live close to a airport.

was looking in to getting a sager laptop for some projects, maybe i have to upgrade my grounding scheme.

heres some pics for ya all. thanks again!

[james]

It's not that a laptop is cheap. It's just the issue of a line lump power supply.

Those are probably not made by HP at all.

Any two prong PS plugged into a 3 wire house system has a floating ground.

Then add to that the fact that the USB is an external thingy...

When I put together component stereo equipment that is all single-ended audio, I often have the same issue. If there is any device in the whole system that uses a 3 prong plug, there is usually audible hum. If I use a (cord) plug with the ground pulled out of it or a ground lift adapter, no hum.

James.

[dchammonds]

Glad to see that you have the issue resolved.

...the one thing that was different when i fired up my projector was i was using a crappy hp laptop in my dining room to play around. back in vt i had all my music mixers and electronic projects always run off my desktop pc. i was like no way i have to check really quick. sure enough the dumb hp laptop (never buy one i had to for work emails on a vacation) is the cause of the signal issue. plugged in to my desktop the skew is resolved and i can properly align optics. cant belive such a silly thing.

I would have expected the opposite- usually laptops offer better isolation than their 3 prong desktop counterparts. Does it make any difference when you run the laptop with the AC adapter vs battery alone?

Besides the desktop, does anything else in your system have a 3 prong plug?

[prosnurfer]

Glad to see that you have the issue resolved.



I would have expected the opposite- usually laptops offer better isolation than their 3 prong desktop counterparts. Does it make any difference when you run the laptop with the AC adapter vs battery alone?

Besides the desktop, does anything else in your system have a 3 prong plug?

ill have to test it with the laptop unplugged. the projector itself has a 3 prong plug input and the ground point on the ac input is where the main ground is for the power supply's. the scanner cards i believe are only grounded through the power supply itself and the laser driver ground is fed to the ilda breakout on pin 25. im wondering if the scanner cards should be grounded through the ac ground instead. i have to do some investigation and never thought of this grounding issue. its funny because when i was doing sound for a part time job i was always worried about this bc i would have to run mixers for events at hotels where they would have me set up outdoors in a court yard where the speaker amps where on a different breaker than the mixer power feed and i would always have to figure out how the event space power distro was set up what a pain.
thanks again for everyone's help. ill do some re configuring of my grounding and try the laptop un plugged. see where i get to and message back with my findings.

cheers!
matt.

[james]

I don't get email notifications from PL because my original (among the very first invitations to this forum) account was "clue by four'ed" quite some time ago; having to do with my adherence to math.

[james]

What you describe is the working implementation of the concept (analog and digital) of floating ground.

As is always... your experience is your own.






.

[james]

If you look at the original images that started this conversation, it looks like the closer the x & y voltages are to each other, the more they are diminished and the father apart they are, the more normal it appears. Not sure what would cause this, but this is literally an x y plot and it is squished along the line x = y.