Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!att!tut.cis.ohio-state.edu!unmvax!bbx!yenta!dt
From: dt@yenta.alb.nm.us (David B. Thomas)
Newsgroups: sci.electronics
Subject: Re: 12V car --> 3V cd player
Message-ID: <1990Dec31.081024.16910@yenta.alb.nm.us>
Date: 31 Dec 90 08:10:24 GMT
References: <41842@ut-emx.uucp> <1990Dec27.141809.2856@phri.nyu.edu> <1990Dec29.070556.7022@qiclab.uucp>
Organization: yenta unix pc, rio rancho, nm
Lines: 19

A hint:  Take the 12v from the battery terminal with its own wire.  Other
wires from the battery have finite resistance and may have high, varying
currents through them, thus providing noisier power.  In particular, avoid
the ignition switch wire.  The "accessory" wire is probably okay.  My car
doesn't have one.

I had a digital circuit that ran from a 7805 connected to the ignition switch
wire, and it would fail when starting the car.  Running a separate wire
from the battery fixed the problem.

I have a big digital circuit in my car (patent pending!) which uses TTL.
7400 series.  Ouch!  Moocho current, poor noise immunity.  But the LM309K
does it just fine.  It has its own wire from the battery, switched on by
a relay controlled by the ignition wire.  (The new version uses CMOS --
I learned those lessons!)

						little david
-- 
This is my .sig.  n?e  .sgurd no gis. ym si sihT