Electronics help

[Shez]

Hey guys.

So I have an theoretical electronics problem for you. In a recent mod I took an old projection panel (see http://www.answers.com/topic/projection-panel?cat=technology) and turned it into a usable LCD screen (for fun mostly) by wiring LEDs on the 12V power source that used to power a fan. The mod was a success in that I could now watch DVDs on the projection panel without having to use an overhead projector.

The problem was that I could see images but there was no onboard sound. Obviously that gets annoying when watching a movie, so I set about figuring out how to get speakers into the thing. Luckily I had a small iPod speaker box. I figured out how to get sound to the speakers and now I can watch and hear movies on my modded (albeit crappy) LCD.

The new problem is that the little speakers are powered by a AA battery. The sound works fine but I really don't feel like replacing the battery because everything else on this build was free and batteries cost money

What I'd like to do is use the 12V source that I'm powering the LEDs from, to also power the speakers. My problem now is that I don't know how to do that. I'd assume that I could use resistors to step down the 12V source to 1.5Vs to power the speakers but I'm not sure how to figure that out.

The speakers are connected to a smaller circuit board that ran off a single 1.5V battery, so I know plugging directly into the 12V source would end in smoke and flames, which I'd like to avoid.

So here's where I need help...
■How can I power a circuit board that takes 1.5Vs from a 12V source (this is all DC).
■Do I need to worry about the amps going into the board? I've tried looking up the amperage of a AA battery but couldn't find it. I'd assume that I should shoot for the same amperage as a AA battery to avoid frying the circuits but wouldn't know how to get that amperage anyways.

Thanks for taking a look and helping me out!

 

[agentsmith957]

Hi, cool to see that someone does these projects still, if i had the time/money id love to fiddle around with something like that. Its definitely possible to do what you need, in a similar manner to what you suggested: you need a resistor network to get the voltage to the point where you need it. Basically, you need to connect the positive end of your 12V source to one resistor, which connects on the other end to your output (which will have 1.5V if you use the right resistor values). This point then needs to be grounded using another resistor (to dissipate the remaining 1.5V to ground). Two resistors which will give you the proper ratio (which happens to be .125) would be a 7.5K resistor and a 1.1K resistor. If you want a simple circuit diagram of what im explaining, PM me with your email address and ill be happy to draw one up and email it you. Happy building!