Electrical schoolwork...

[mike]

12V LEDs are widely available....Maplins or RS in the
UK, Radio Shack in the US, your local electronic shop
in the rest of the world

If you fancy the rice boy look you can also get
flashing 12V ones

Mike

 --- Louis-Alain RICHARD <laraa at sympatico.ca> wrote: >
Wonderful ! (LOL)
> Thanks guys!
> 
> I knew a question like this one would raise
> interest...
> 
> So, after all this, here is what I can add:
> 
> Like Ameer said, the 150 000 ohm figure is probably
> not useful since it
> depends on the DMM voltage. I did not knew this, now
> I (and all of us) do.
> This figure comes from a batch of green 3V LED I
> have here. 
> 
> After all these posts, I went to the basement and
> made some measures.
> However, I don't have any useful source for 12V in
> the house so let's play
> with 3V.
> 
> 2 new AA batteries (2.8V total) 
> various ohm resistances
> 3 green LEDs.
> 
> 1 LED connected to 2xAA: very bright green, 2.7 Volt
> across the leads, not
> able to measure any current with my DMM (when
> series-wired).
> 
> 3 LEDs in parallel connected to 2xAA: 2.48 Volt
> across, still bright green,
> still no current figures.
> 
> 1xLED and 1x 500 ohm in series: dim LED, 1 volt
> across the resistance, 1.8
> volt across the LED.
> 
> Does this confirm Ti and Ameer numbers? I guess so.
> 
> But then I have a problem (like Huw said): my
> initial thought was that a
> small LED and a small resistance would be easy to
> insert IN the switches at
> the burned-bulb place (I already opened all the
> switches last year to check
> if it was feasible to replace only the bulbs:
> negative...). But now if I
> have to package a big 1W resistor IN the switch, it
> might me very
> challenging. 
> 
> Hum...
> 
> The other solution would be to insert only the LEDs
> and find a way to place
> a single resistor elsewhere and carry an additional
> 3V wire to the different
> LEDs... A good way to ruin perfectly good switches
> and wiring...
> 
> Or maybe if I can find some 12V LEDs, all this
> discussion would be a huge
> WOB...
> 
> Yeah, thinking of it, this would be the ideal
> solution.
> 
> Is such a LED exists? A long life, wide temp range
> 12V red LED?
> 
> Answer tomorrow, after my visit to my NFNKLEPS (not
> friendly, not
> knowledgeable local electronic parts store)!
> 
> Louis-Alain
> 1983 urQuattro
> 85-D-900463
> 
> 
> 
> 
> -----Message d'origine-----
>  De la part de Ameer Antar
> 
> Although the current wasn't given, this really the
> only way to calculate
> anything for an LED. The resistance of an LED
> depends on the voltage used by
> the meter, and that's usually not something written
> anywhere. So the
> resistance reading of an LED is not very useful, and
> I've never seen written
> on a spec sheet. That's b/c an LED is not a simple
> resistive load like a
> light bulb. It's basically a diode which changes
> states rapidly as voltage
> changes. That's how transistors and such can switch
> on or off in the digital
> world.  Oh, and the 15mA is just a usual figure for
> red LED's... it maybe
> more or less, but it's unlikely to be far off from
> that unless it's one of
> those ultra-bright's or blue-colored LED. Hope this
> clears things up a bit.
> 
> -Ameer
> 
> ---Original Message---
> Date: Tue, 10 Feb 2004 01:57:48 -0500
> From: Huw Powell <audi at humanspeakers.com>
> 
> I prefer this answer to Ti's current based
> calculation.
> 
> I would recommend testing your choice "out in the
> open" before 
> rebuilding a fistful of switches, etc., to make sure
> you got it right.
> 
> -- 
> Huw Powell
> 
> http://www.humanspeakers.com/audi
> 
> http://www.humanthoughts.org/
> 
> 
> _______________________________________________
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> quattro at audifans.com
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