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Author Topic: Using Apple Lisa with projector VCF East 2021  (Read 106 times)

compu_85

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Using Apple Lisa with projector VCF East 2021
« on: October 29, 2021, 04:49:51 pm »

The video out from the Lisa goes through a cabling adapter to the R G and B pins on a VGA plug.

Some more details here: https://twitter.com/compu_85/status/1441753541413150722

One change I made was to parallel another resistor on the output of the Lisa, so that it drives the signal a little harder: The 3 lines in the projector are each terminated, and having all 3 hooked up at once drags the signal down a bit making it dim.

The projector is an InFocus IN118HDa. This trick doesn't work on all projectors, but that older infocus supports EGA resolutions, which the Lisa signal is close to.

-J
« Last Edit: October 31, 2021, 09:14:49 pm by Lisa2 »
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Lisa2

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Re: Using Apple Lisa with projector VCF East 2021
« Reply #1 on: October 31, 2021, 09:31:13 pm »

This is great! 

I am trying to understand how this is working.  Does anyone here know?   I get connecting the signal output of the Lisa to the 3 RGB inputs to make a mono ( B&W ) display, but how in the world is the projector understanding the sync signals?   I know sometimes it's common to have "Sync on Green",  just I am not aware of any VGA display that uses sync on green as an input.   

You said this projector is somewhat "old school" by support EGA resolutions, but it sure seems to be a pretty modern DLP device with a HDMI input and all. 

Again, help me understand how this projector is syncing with out the sync inputs connected?  Do other modern digital displays just ignore the VGA sync signals and somehow use the RGB inputs alone?   

Thanks,

Rick
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patrick

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Re: Using Apple Lisa with projector VCF East 2021
« Reply #2 on: November 01, 2021, 04:36:37 am »

Yes, to allow this type of connection the projector has to accept sync-on-green. So actually only two cables need to be connected, green and ground.

If you have a projector old enough to handle EGA, chances are good that it can also do sync-on-green.
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blusnowkitty

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Re: Using Apple Lisa with projector VCF East 2021
« Reply #3 on: November 01, 2021, 10:56:53 am »

Interesting... I'm pretty sure I don't have a sync on green projector, but I know I've got a couple of LCD panels that'll take it cause I use them with my SGIs. I'll have to try this.
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compu_85

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Re: Using Apple Lisa with projector VCF East 2021
« Reply #4 on: November 01, 2021, 09:21:46 pm »

Yes, this projector worked with the output from the Lisa hooked up to the green pins on the VGA plug.

I hooked up all 3 so that the picture would be white.
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