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# TJBraza

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1. ## Car battery to parallel port

Thanks again MP for your time (and patience) :-) One more: How would a LM7805 fare in a running car? If I read the voltage on my car while it is running, it goes from 11v to 14v, depending if the air conditioner/stereo or whatever is turned on or not. Would the LM7805 need a decoupling capacitor in that case (I'm not sure which capacitor to use or how to wire it, so it'd be great if I didn't need one)? Or is the LM7805 not suited for circumstances where the input signal is not stable and there are peaks from the crank etc?
2. ## Car battery to parallel port

Hello. MP: I just need to know if a switch that's connected to a car battery is on, or off. So basically just knowing if the battery/switch is outputting anything will do fine. If I'm not mistaken, a 5v on a (few) certain parallel port pins will give me a "high" reading, right? So basically all I have to do is create a resistive divider that will drop the voltage to 5v AND the current to a few miliamps (or whatever the parallel port can cope with), correct? Omni: I'll look into the IC but I think it's a bit overkill for my purpuse. Thanks guys for the input.
3. ## Car battery to parallel port

Hello friends. I'm a newbie at the forum and (very much) a newbie at electronics. I intend to monitor a car battery's status (live or dead) using the PC's parallel port. From the looks of it, the inputs on a parallel port work at 5v, so I'd have to put at least one resistor to drop the battery's 12v to 5v so the port's input will give me a "live" reading. My problem is that the battery has 60amps and I don't know how to connect that to the pc's parallel port and not fry the port. In my understanding, I have to connect the (reduced to) 5v positive from the battery into a (non inverted) input pin on the parallel on the pc, and the ground from the battery on one of the ground pins on the parallel port. But if I do that, won't I instantly fry the board (and my computer too)? How should I go about this? Thanks for any input!
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