# 12vdc to 1.5vdc for car

Discussion in 'Electronic Basics' started by Bach Mai, Dec 28, 2003.

1. ### Bach MaiGuest

I am trying to set up a circuit for a clok in my car that will take
the 12v from the battery and output 1.5v to a clock, I need the
circuit to fit inside a gauge pod that is 3 inchs in diameter and
about 2 deep, thanks for any help

2. ### NormGuest

So you need 12VDC to 1.5VDC C.
Why don't you use a 1.5v Battery?

3. ### John PopelishGuest

You need to measure the current the clock draws from a 1.5 volt source
(like a dry cell). The regulator may be as simple as a dropping
resistor and a red LED as a voltage clamp and perhaps, a capacitor,
across the clock terminals.

4. ### MichaelGuest

The first thing that comes to mind would be a variable voltage regulator.
My favorite would have to be the LM317 (datasheet:
http://www.national.com/ds/LM/LM117.pdf) Check out the circuit called
"Adjustable Regulator with Improved Ripple Rejection" on page 14 of that
datasheet. That should be exactly what you need. I dunno what kind of
current your clock needs - but it's probably pretty low - so you won't need
too substantial of a LM317 - since it *probably* won't be dissipating too
much current. I should think one in a TO-220 package should work just fine

Now I was just thinking - so you'll have to tune that circuit to 1.5V. No
sweat when you have a nice constant 12V to work with. But I've heard that
voltage in a car's electrical system can spike to as much as 100V DC -
which would throw that circuit off quite a bit. Maybe someone else would
have some input as to how to smooth that out?

Good luck, and have fun!

Michael