Re: bi-color LEDs with mixed common lead

"Roger Hamlett" (rogerspamignored@xxxxxxxxxxxxxxxxxxx) writes:
"Carrie" <cnuncio@xxxxxxxxxxxxx> wrote in message
news:76pPg.8395$LH2.1473@xxxxxxxxxxxxxxxxxxxxxxx
Starting on a new PIC project using bi-color LEDs. First thought was to
use
a hex inverter to change colors between RED and GREEN. However it
occured to me that if there were a bi-color LED (RED/GREEN) that had a
mixed
common lead it would save me 4 74ALS04 hex inverters, the board
real estate and the board size. I can find common anode and common
cathode
LEDs but, so far, no mixed common. By mixed common I mean that the
anode of one LED is internally connected to the cathode of the other
LED.

Anyone heard of such an animal??
They are common, but becoming rarer.
Historically, the first 'bi-colour' LEDs, used this design. Latter designs
with three leads, are commonly called 'tri-colour' LEDs (though of course
the 'bi-colour' units can also generate the third colour by being fed from
AC). You can turn a tri-colour design into a bi-colour unit by just
joining the outer pins on the package, and hence these are generally
getting to be more common. Look at:
http://www.hvwtech.com/products_view.asp?CatID=99&SubCatID=225&SubSubCatID=0&ProductID=358
What you have at the moment, is normally called a 'tri-colour' design.

Best Wishes


Wait a minute.

An old style bipolar LED has the two led's arranged so
the voltage one way lights up one LED, the opposite polarity
lights up the other (both the left and right sides are connected
together):
--->|---
--|<----

But the three lead LEDs have them arranged so (with the common lead
being either the left or the right side, I forget which):
----|<---
----|<---

If you parallel the two other ends, all you get is two different
color LEDs that light up at the same time. There is no way of
changing color.

Michael

.

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