Hey Guys,
I haven't seen much support regarding more complex electronic control for a custom projector... so I devised one:



Hopefully you can follow the design - all the magic happens in the "Electronics Box." It is powered by a 12V adapter. The main power switch is designed to always be swtiched on (like your computer's main power switch (if it has one)). What makes this design awesome is that it is entirely controlled by the monitor's control panel (the monitor's power switch). It turns on the LCD panel, the lamp, and the fan. This design also includes a feature that keeps the fan running for a minute or more after the monitor has been turned off. The Backlight Cable from the monitor is used to tell the Electronics Box to turn on the ballast and fan. This design can also be adjusted to have a temperature-sensor to control the fan. The reason why the relay is important is so that there is one button to turn the machine on and off and still be able to keep the fan running (so you cannot simply turn off the main power switch).
Schematic diagrams of the electronics box may come soon. I still have to figure out certain properties regarding the backlight, timing for fans (or temperature-sensor alternative), and other things.

Any comments or criticism is most welcome

The idea is certainly nice. I hope to design a circuit in the future (need to get the pj working first) that will control the fans by setting two speed modes. By using a thermistor, I can measure the heat at the screen so that if it's below a certain temperature the fans will run low, but then if it gets warm the fans will run at full. The circuit will also run the fans for 10 minutes at full when everything is turned off in order to cool out the box. There will also be a high temp alarm which would automatically turn the lamp off and run the fans for 10 minutes if it exceeds some temp threshold (several degrees below the limit but not so low that it goes off the whole time). It would also have a turn-on inhibitor so that the lamp could not be turned on again fro 10 minutes. It'll take some time to develop this, but would certainly be useful. I might go microcontroller with it and even have an LCD to display data (time, temp, lamp life, etc...). Nice things to have, but don't necessarily need.

Good luck with your design efforts.

David

Hey, I was reading your post, and since it related to a design I have already made, I
went ahead and made a thread for my power circuit design. Check it out:
Power Circuit

one potential "gotcha" that you will need to be careful about.

Most LCD monitors have a function where in the "no signal" states on the input, the monitor will power off the backlight for a second.

If you do this with a MH lamp, don't expect it to power right back up again like the stock backlight did. It won't. It will take a minimum "restrike time" to come back. Since I know that my PC does this when switching resolutions, I decided NOT to use the backlight signal to turn on my lamp. I did think that maybe the power LED line would be okay though.