audi at humanspeakers.com
Tue Feb 10 02:31:49 EST 2004
> Although the current wasn't given, this really the only way to
> calculate anything for an LED.
So why aren't you guys asking him for the current rating for the LED?
Wihtout it, you're just shooting for the hip...
> Oh, and the 15mA is just a usual figure for red LED's...
Since this was an assumption, it should have been stated (ie, "for a
> Basic electronics 101 here. I thought you'd know that well, but
> apparently not.
I'm holding my own with Ohm's Law, thanks...
> An LED is not a resistive device, thus you cannot calculate based on
> that assumption. An LED is a light emitting *DIODE*. It has a
> relatively FIXED forward bias voltage. That 150K ohm "LED
> resistance" is an irrelevant spec. What *is* important is the
> forward bias voltage and current requirement of the LED, and the
> total supply voltage. Then the required resistor value can be
> calculated from that.
Yes. If he had stated the current rating, your calculations would have
had some merit. As it was, you introduced an unstated assumption. As I
said above, without the current rating of the LED, you're just winging
it. They do range, after all, over at least an order of magnitude, right?
And, of course, I should also have noticed that the basic spec was
missing at the start. The dust will settle while the rest of the list
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