Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!wuarchive!emory!rsiatl!jgd
From: jgd@rsiatl.UUCP (John G. DeArmond)
Newsgroups: sci.electronics
Subject: Headlight buzzers (was Re: Car Battery Rechargers)
Message-ID: <4233@rsiatl.UUCP>
Date: 9 Oct 90 00:14:43 GMT
References: <13766@mcdphx.phx.mcd.mot.com>
Organization: Radiation Systems, Inc. (a thinktank, motorcycle, car and gun works facility)
Lines: 50

hbg6@citek.mcdphx.mot.com writes:

>>Since my concern was from leaving my lights on and not cold weather, I
>>am now considering building a device I saw in a popular electronics
>>magazine that buzzes if you leave your lights on.  (I don't have the
>>magazine with me but can give details to anyone who wants more

>In my wifes car, I installed a relay in series with the headlight relay
>that insures that if the key is off, the headlights are off.

>Interestingly, our '75 Volkswagen van has this feature built in but it
>only turns off the headlights, not the running lights.

My wife's Camrey has its own little computer to figure out when to
turn the lights off.  What'll they think of next to put some silicon
in? :-)

Making a is trivial.  All one needs is a Sonalert or similiar device
and a 1 amp diode (1n4002 works well).  connect the diode in series
with the sonalert with the cathode connected to the (+) lead of the 
sonalert and the anode lead ready to connect to wire.  Locate a point
where where there is swiched 12 volts from the ACCessory switch position.
This is usually marked on the fuse block.  Next find a place where there is
switched power to the headlights.   The dimmer switch and/or the headlight
switch are obvious places.  Connect the Sonalert assembly such that the
(-) side of the sonalert is on the ACC switched 12 volt lead and anode of
the diode is on the switched headlight circuit.

The circuit works as follows.  When both the ignition and the lights are
on, there is 12 volts on both sides of the sonalert and thus no current
flow through it.  When the lights are off and the ignition is on, there
is voltage on the (-) side of the Sonalert and there is an effective 
ground through the headlight filaments.  The diode is reverse biased,
however and the sonalert remains quiet.  With the lights on and the 
ignition off, the anode of the diode and therefore the (+) side of the
Sonalert is at 12 volts while the (-) side of the sonalert is at an 
effective ground through the de-energized load on the ACC terminal.
Since the diode is forward biased, the Sonalert sounds, alerting you to
turn the lights off.  

Simple, reliable and only 2 components involved.


John

-- 
John De Armond, WD4OQC  | We can no more blame our loss of freedom on congress
Radiation Systems, Inc. | than we can prostitution on pimps.  Both simply
Atlanta, Ga             | provide broker services for their customers.
{emory,uunet}!rsiatl!jgd|  - Dr. W Williams |                **I am the NRA**