🚀 go-pugleaf

In article <1491@imagine.PAWL.RPI.EDU> snyderw@pawl1.pawl.rpi.edu (Wilson P. Snyder II) writes:
>Since everyone is on the topic of LEDS - I have a little problem.
>
>I need a LED that will display RED, GREEN, and a decent YELLOW.
>
>I have experimented with about 10 R-G Tri-Pin LEDS  (Three leads)
>The problem is that none of them form acceptable yellows (the yellow
>should be like a yellow LED.)
>
>If I over drive the green element (IE 100 ma instead of 20ma)  I get a
>nice yellow, but of course the LED self-destructs.
>
>I also know about the two pin bicolor LEDS where you pass AC through the
>device.  I would prefer not to have to use this type, but if I must I
>must.  I expect that I will have the same problem getting good yellows though.
>
>Oh, yes, I do need the GREEN and RED also, so don't suggest Green/Amber LEDS.
>
>
>
>______________________________________________________________________
>Wilson P. Snyder II                snyderw@pawl.rpi.EDU
>15 Davis Parkway                518-276-2764
>So. Burlington, VT 05403        802-658-3799 in summer (That's now)
>______________________________________________________________________

I ran an experiment with the following circuit:


                      +5
             ----------|----------
             |                   |
             R1                  R2
             |                   |
             |_____RED LED_______|
             |     GREEN LED*    |
             |                   |
             |----------         |
             o         |         o
            / \        |        / \
           /   \U1a    |       /   \U1b
          -------      |      ------- 
             |         |_________|
             |
             |
             |
             |
          -------
          |     |
          | 555 | I actually used a frequency generator but
          | Osc | would use a 555 oscillator in a real circuit.
          |     |
          -------

R1, R2 - 220 ohm
U1 - 7406 open collector inverter
* - The LEDS are facing opposite directions. I used 2 discrete LED's because
    I didn't have a bi-color laying around.

This flashes the two LEDs. I figure that by changing the frequency and
duty cycle of the 555 and by changing the values of R1 and R2 you can
get a good yellow from a bicolor LED. Also  you can drive the LEDs above
their rated values if you pulse them.

Some simple control (like a nand gate) should allow you to get just
red and green. If you overdrive them thoughyou'll need to gate with the
oscillator.

BAJ
-- 
Another random extraction from the mental bit stream of...
Byron A. Jeff
Georgia Tech, Atlanta GA 30332
Internet:	byron@pyr.gatech.edu  uucp:	...!gatech!pyr!byron