Re: bi-color LEDs with mixed common lead

"Carrie" <cnuncio@xxxxxxxxxxxxx> wrote in
news:76pPg.8395$LH2.1473@xxxxxxxxxxxxxxxxxxxx:

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??

Thanks !


I've not heard of them, but if you can make a rail of half your supply
voltage (must source and sink, so op-amp driven is best), you could use
two-lead bicolour LED's, and a single resistor for each. High output would
send current through it one way, low would reverse it. You save a resistor,
each LED needs only two connections, and although it might be overkill for
a handful of LED's it might be ideal for lots of them. The main problem I
can see is the need for a very low value resistor and a very well regulated
supply if it's 5V, because half of that doesn't leave much headroom.

.

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