Flashing LED's

Subject: Flashing LED's
From: jeff.tatum@domain.elided (Jeff Tatum)
Date: Sun, 4 Dec 1994 18:00:52 GMT
> I went digging and I found a rough schematic and a bunch of the needed
> parts.  I don't have the schematic in any electronic format at
> present. Making the thing is not very straight forward. I believe
> putting togeth step by step precise instructions is something that
> would take more time than I have.
>
> It is made from:
>
> - - 1 digital timing chip
> - - 1 transistor
> - - 1 MOSFET
> - - several resistors
> - - 1 capacitor
> - - Small PCB board
> - - Bus wire
> - - Std insulated wire
> - - 1 LED
>
>
> I made one up Wed. night and I guess it took me about 1 - 1 1/2hrs or
> so
<snip>
> to make them. I was thinking maybe $15 & $30 respectively.  Anyone
> still interested just e-mail me.
>
> Jimmy Shrake

Or, if you want to do it the easy way <grin>, just go to Radio Shack and
buy a flashing LED (they have them), and wire it between the a constant
12v (anode) and a switched 12v source (cathode) - like the memory wire
and the main power wire to your radio.  When the key is on the two lines
are at the same potential and the LED is off.  When the key is off,
there is enough difference in potential to power the LED.  You may have
to use a current limiting resistor in some cars, but that's it.

Really.  It works.  I've done it many, many times.  The only time it
didn't was in a Chevy fullsize truck that didn't have enough current
draw from accessories to power the LED. In that case, a resistor from
the switched side of the power to ground fixed it (1k I think). Later
BMW's with all the gizmo's shouldn't have this problem.  If you don't
want to do that, just leaving on, say the blower motor switch or
other accessory will do the same thing.

Cost: About two bucks.  Three if you buy a grommet.
Time: 'bout 15 minutes.  Just pop out your radio, hook it up, and put
      the LED in one of those pop out panels for accessory swithes near
      the radio

- - Jeff ("retired" car stereo/alarm installer)


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     Jeff Tatum                     jeff.tatum@domain.elided
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