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[lcdproc] FW: Question: How to connect an LED to GPO of Matrix Orbital.


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  • From: dglaude AT netbrain.be (David Glaude)
  • Subject: [lcdproc] FW: Question: How to connect an LED to GPO of Matrix Orbital.
  • Date: Tue, 19 Sep 2000 19:08:31 +0200

Hello,

I know everytime I talk about electronics I sound stuppid...
But it seems that some LARGE LED will survive, smaller one might need a
resistor.
There is already have a very small resistor in line. (Good to if especial
when you don't understand).
But obviously ROB know something both about ELECTRONICS, MATRIX ORBITAL and
LED.
He even know the formula and a friend of mine already did try to explain me
the same stuff 3 times.

Don't trust my words, read this mail from Rob.

David GLAUDE

PS: What know, is that if you put a too strong voltage/impedance(?) on a LED
(if good polarity):
"The LED turn ON, STRONGLY, for a SHORT TIME, and then NEVER AGAIN."
;-)
And this is a practical experience I have had many time. :-(
Any success story?

-----Original Message-----
From: Rob Hansen
[mailto:rhansen AT matrix-orbital.com]

Sent: Tuesday, September 19, 2000 6:26 PM
To: David Glaude
Subject: Re: Question: How to connect an LED to GPO of Matrix Orbital.


David,

Not sure what that was all about, but the GPO's have a small
resistance (240 ohms) in line. They do not provide 5 volts when on,
but rather, supply a path to ground when on. This is not important
really for LEDs - just clarifying.

Since the voltage drop across your average LED is about 2.5 volts,
and the inline resistor is 240 ohms, you can find the current by
V=IR.
I = V/R
I = 2.5/240
I = ~ 10mA

10mA is appropriate for a fairly large LED (T1 3/4). It may be a bit
much for some. Check the specs for the ones you intend to use.

Rob Hansen



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  • [lcdproc] FW: Question: How to connect an LED to GPO of Matrix Orbital., David Glaude, 09/19/2000

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