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I made the assumption that they would discharge at more or less the same rate thinking you would need a pretty big difference in voltage or impedance between the two batteries otherwise, though thinking about it more after you pointed it out, the difference in impedance could have a pretty big ...

If you hook up two batteries in parallel, depending on the battery type and how well the cells are matched (impedance wise), you may run into the issue of the batteries slowly discharging themselves (faster than they would if just left sitting). Also, if one of the batteries has a lower capacity ...

Running 8V through something that is made to take 7.5V will not harm anything
Maybe not for whatever he's working with, but in general this is not a good assumption to make. There are plenty of parts out there with fairly tight supply voltage tolerances, and there's always the chance that whoever ...

And BTW, I don't make enough to splurge $200 on a projector, and that's why I wanna either make one that costs less than $100 or just buy the $99 one from HA. I mean, would it make a difference to anyone or just a die-hard videophile?

I think it would absolutely make a difference to anyone. I ...

Yes, it will work. I have a few of these lying around and used to use one in my N64 portable. "Memory" probably won't be an issue because with the amount of current you'll be pulling from them you're likely to discharge the batteries enough when you use them, but if you're really concerned you can ...

It would work, but not very well. In order to avoid burning current through the resistor when the switch is set to 'off', you would need a much larger resistor (a few k-ohms at least), but then you would only get a couple mA at most through your LED. Depending on the LED you use and how bright you ...

It's a little hard to tell from the reflections on the ink, but it looks like you don't have the potentiometers in the right spot (assuming those are LM350's). You should have the fixed resistor between the output and adjust pin (like you have drawn), but the pot should be between adjust and ground ...

You should not need a 1W resistor, and using one isn't likely to change how much heat is produced by this circuit. Even if you're using a 12V battery, the most current that can pass through the resistor is 12mA (assuming the transistor is a perfect switch, so even this is a little high), which means ...

For most electronics, the term ground in itself just implies that it's the reference point (as opposed to being earth ground). It's not uncommon to have multiple grounds in a circuit, such as a ground for digital and a separate ground for analog signals, in order to prevent noise from one part of ...

According to the datasheet for the screen module, the backlight takes 690Vrms, so just probing around on the transformer while it's running may not be the best idea.

Aside from that, the transformer alone is useless; if you hook up 7.5VDC to it, you'll have nothing more than an oversized resistor ...

I've never seen it done before either. The only time I can think of that you might run into the problem you described would be if you have a bi-directional device (or something isn't working right, in which case you have other problems). If that is the case you may be able to configure the I/O pins ...

Don't know if this is practical but how about using a TI step-down regulator to generate 1.5v (or just above) from the 7.5v batteries, then put this in series with the battery power, to get 1.5v + 7.5v = 9v; and take a line from the same batteries for 7.5v ?

Might be worth a try.

This won't ...

The LCD driver on the screen board is fed straight off of the 7.5V input, so you definitely do not want to power it without something to regulate that voltage. I'm not familiar with the x-box version of the screen, but the gamecube and PS2 versions have a really dirty regulator that relied on the ...

The datasheet for the screen module (LCD + backlight) says 10000 hours minimum (note that's 10k hours before it drops below 50% brightness), but that's based on ideal operating conditions and in reality it may not actually last that long. It depends on the driving circuitry used on the control board ...

A single 300 ohm resistor should work just fine, it will just be about half as bright as it would be with a 120 ohm resistor. The general current and voltage specs for LEDs are fine if you're using them at those levels, but as timmeh87 said if you really want to know what's going on you need to look ...