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Old 12th November 2005, 05:53 PM   #101
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Well Im not going to do this experiment today!

The reason is, My testbed projector is throroughly integrated with the p-brain which now controls everything. I would have to reinstall mechanical switch based bypasses to circumvent the p-brain's control.

Im willing to do this for the sake of testing... but not today!

Ive decided instead to discuss this point on a Theoretical basis.

Is Glass an Insulator?

Most definitely!

However.... not a perfect one.

Pick up a glass full of boiling water... if you dare.

Glass is a fantastic electrical insulator, but its Thermal insulation characteristics? Completely different.

This being the case, I believe that cooling the exterior of a MH bulb via fans... can result in its interior cooling faster than room temperature based cooling alone.
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Old 12th November 2005, 11:36 PM   #102
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Default cooling

You can certainly cool the outer glass by blowing more air on it, but you can't make the gas circulate any faster inside the outer envelope. Heat is transferred away from the arc chamber by two different mechanisms: Convection and radiation.

Radiation is in the form of long wave Infrared emission. That passes through the two layers of glass, and the outer gas mixture with little loss. As long as the long wave emissions from the outer glass are weaker than the arc chamber emissions, heat will be transferred out. (If the outer glass was hotter than the arc chamber, then heat would actually be transferred into the arc chamber, but this never happens.) Cooling the outer glass from say 180 F to 80 F would have little effect on heat transfer by radiation, since the arc chamber is so much hotter.

Convective heat transfer occurs when gas inside the outer envelope is heated by contact with the inner envelope glass, and then moves physically to the outer glass surface. Some of the heat is transferred by contact with the outer glass, if that surface is cooler than the gas. Blowing air over the outer glass surface will remove that heat and keep convective transfer going.

But: I don't think there is a lot of convection going on inside the outer envelope, because there may not be much gas at all in the outer chamber! I know that some of these lamps have a pretty high vacuum in there, with fusable links to break the circuit if air leaks in. This is so the outer chamber can contain a rupture of the inner chamber during operation. When the mercury in the arc chamber changes from liquid to gas, the pressure in there goes way up. If the inner glass pops, then that small volume of high pressure gas equalizes with the much larger outer chamber, stops the arc, contains broken glass and other hot bits, and that cools the mixture enough so the mercury goes back to liquid phase. If the outer chamber is mostly vacuum, then almost all the heat transfer will be by radiation.
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Old 13th November 2005, 10:22 PM   #103
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The only true way to figure this out if via testing...

Anyone out there have a Projector with a switch for the fans and a switch for the lamp?

I did kind of try to do this test with my PJ.

What I did was boot it and let it run for 20 minutes or so, then unplug it and try to restrike. The p-brain was able to get the lamp to restrike within 4 minutes... BUT the fans were running when it rebooted because of the p-brain so that definitely skewed my results.
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Old 15th November 2005, 04:24 AM   #104
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NEW REVELATION....

If I put the front cover (which contains some kind of curved white lens) back onto the motion detector... It detects motion MUCH more easily...

So now... waving an arm triggers the motion detector quickly, and consistently.

Hmmmmmmmm....

This being the case... I may want to modify my assumptions for the design of p-brain 2.

What I think I will do... is leave all options open, and add funtionality to the design instead of substituting. If I want one of the next projectors I build to be triggered by motion, then so be it... if not, the motion detector is easily bypassed by just removing the detector (in this case the p-brain will always see motion) and IR remotes could be used to trigger it.

Thus far, Im really digging the controller thing... I no longer worry about the projector. Right now Im looking at a movie on it... when I decide to get up and go to bed, Ill just get up and walk away knowing that the PJ will take care of itself.

Its not perfect just yet though... I still need failure mode detection to be integrated: Fan(s) fail... bulb fails... temp rises too high...etc.

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Old 4th December 2005, 05:49 PM   #105
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After running the P-Brain V1 DIY Projector Controller for a month in my testbed projector, I must say... I really like it. With this kind of thing you never really know if youve gotten something worthy until you actually use it in a real world situation for a while.


From here Ive been considering a couple of different options... one of which is to enhance the P-Brain V1 functionality.

The other is to head towards a slightly lower tech Projector Control direction...
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Old 4th December 2005, 06:02 PM   #106
tjh is offline tjh  United States
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What do you mean lower tech? P-Brain not working out?
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6/12/06: Redesigning everything, finally putting in the Ushio S400DD.
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Old 6th December 2005, 02:33 AM   #107
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so is your lcd projector an OHP style and you took monitor apart?

or is this one of those reflective boxes so you did not take monitor's backlight out?

just asking cause i need to find out which lcd is good for an OHP project (i destroyed two lcd's already)
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Old 6th December 2005, 10:01 AM   #108
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Quote:
Originally posted by tjh
What do you mean lower tech? P-Brain not working out?
Its working out fabulously. Runs flawlessly. I wouldnt even consider building a projector without one. I'm currently desiging Version 2 which will have all the Version 1 capabilities plus.

Actually... now that I think about it "lower tech" might not be the best way to describe what Im planning, because it could actually be more technically challenging than the original design depending upon how I spin it. I think a more accurate description might be that Im considering a more modular approach to this. The reason is... Ive come up with other ideas that I dont necessarily know If I want to incorporate directly into the controller board, have them be integrated as add on modules, or have them be implemented as completely independent systems. Some of these ideas could theoretically be implemented and used independently of having an intelligent controller present, so Im considering whether or not to just keep adding features to the P-Brain, or build some functionality that is capable of working stand alone.

If I were to implement (or at least prototype) some of these features as stand alone independent systems, those independent systems would be "lower tech" than the P-Brain itself, because they arent all encompassing, intelligent control systems

Quote:
Originally posted by snortonnorton
so is your lcd projector an OHP style and you took monitor apart?

or is this one of those reflective boxes so you did not take monitor's backlight out?

just asking cause i need to find out which lcd is good for an OHP project (i destroyed two lcd's already)
My testbed projector uses a stripped BenQ 567 in a custom built box.
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Old 6th December 2005, 04:00 PM   #109
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ok but i still dont' know if you mean your lcd panel is without backlight and is sitting ontop of OHP?

or did you keep the backlight and it's in one of those reflective boxes?


I got a nice Dukane that is really bright OHP so i want to just use lcd panel no backlight.

but after destroying two lcd's trying to remove backlight should i just build a reflective box like you guys?
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Old 6th December 2005, 08:37 PM   #110
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Im not using an OHP... the backlight has to be removed no matter what you use. You just have to be really careful handling the LCD once its stripped.
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