On Thu, 21 Jan 1999, Hash wrote:

> I have a 1970 camaro and I am trying to use LED's for as many things as I
> can and keep the car looking stock. I have some super bright white LED's
> that run off about 30 mA each and work pretty good here in my room but I
> know in daylight it will not be so great.  I built a circuit and I have been
> pulsing the LED with approx 80-100mA (according the the inline current
> sensor) and it is VERY bright and seems to be able to take it for quite a
> while(tested for 3 hours).  Once I have 4 LED's on there though, I am
> actually drawing more power than the light bulb took.  My main goal is to
> reduce power consumption in my car from as many spots as possible.  Has
> anyone pulsed LED's like this and have any advice for me?  Any information
> is greatly appreciated.  I have been varying the on/off times of the pulse
> to achieve what I feel is a happy medium so the LED is bright but won't harm
> it.

I recently did a project involving a large array of LEDs driven by a
matrix of transistors, no current limit resistors, just a 1K resistor
between each transistor base and the PIC pin driving it. I used a 10K pot
from Vdd to ground with the wiper connected to an analog input on a
16F877.  I use the analog reading from the ADC to set the ON time of
pulses occurring at regular intervals (using an interrupt from TMR0), so
you have an analog brightness control without the analog drive to the
LEDs.  Works great and the code is really simple.  If you're going to use
LEDs in the dash/interior of the car you might want to try something like
that.

As I understand it, LEDs can take some pretty impressive current if the
duty cycle is low enough...  I think you just figure the average current
and keep it within a reasonable range.  I'm SURE someone here will quickly
correct me if I'm wrong!  8-)

Dale
---
The most exciting phrase to hear in science, the one that heralds new
discoveries, is not "Eureka!" (I found it!) but "That's funny ..."
                -- Isaac Asimov

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