Re: bi-color LEDs with mixed common lead

"James Thompson" <Jamesthompson2002@xxxxxxxxxxx> wrote in
news:94e5e$4513fad9$438c85c9$9586@xxxxxxxxxx:

I see what you mean about using the opamp for the divider. With my
resistor divider, I was not meaning only 1 divider for the whole 24
led array. Also they could consider a divider using 2 zener diode in
series to stiffen the reference voltage. Still like you say, it would
be best if they could find high efficiency led's.


Zeners are neat, but a tad temperature sensitive. LED currents would change
their temperatures enough to risk the headroom available. The PIC should
already be on a well-regulated supply, it just needs accurately to be
halved, hence the voltage divider and the op-amp.

I take your point about the divider per LED, but I'd rather solder two
resistors and one op-amp than 46 extra resistors.

The op-amp would be a neat idea even if there was only a couple of bicolour
LED's to think about. It might be worth rethinking the LED format to adapt
to this, but I seriously hope that manufactures start making bicolour 1.8 V
LED's bearing in mind this kind of use on a 5V/2.5V rail system. 1.8 V
LED's are usually high brightness types, so it would allow running on as
little as 5mA. For reasons totally inexplicable to me, there don't seem to
be standard indicators using this type, and there should be, makers would
have no trouble shifting them in thousands.
.

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