Electrical schoolwork...

[Ameer Antar]

Although the current wasn't given, this really the only way to calculate anything for an LED. The resistance of an LED depends on the voltage used by the meter, and that's usually not something written anywhere. So the resistance reading of an LED is not very useful, and I've never seen written on a spec sheet. That's b/c an LED is not a simple resistive load like a light bulb. It's basically a diode which changes states rapidly as voltage changes. That's how transistors and such can switch on or off in the digital world.  Oh, and the 15mA is just a usual figure for red LED's... it maybe more or less, but it's unlikely to be far off from that unless it's one of those ultra-bright's or blue-colored LED. Hope this clears things up a bit.

-Ameer

---Original Message---
Date: Tue, 10 Feb 2004 01:57:48 -0500
From: Huw Powell <audi at humanspeakers.com>
Subject: Re: Electrical schoolwork...
To: SJ <syljay at optonline.net>
Cc: quattro at audifans.com
Message-ID: <402880EC.1090505 at humanspeakers.com>
Content-Type: text/plain; charset=us-ascii; format=flowed

I prefer this answer to Ti's current based calculation.

I would recommend testing your choice "out in the open" before 
rebuilding a fistful of switches, etc., to make sure you got it right.

SJ wrote:

>>From: "Louis-Alain RICHARD" <laraa at sympatico.ca>
>>
>>Resistance value of the LEDs: 150 000 ohms 
>>Ideal voltage at the LEDs: between 2.5V and 3V.
>>Electrical voltage at the switches: 13.6V, permanent, switched by the
> 
> 
> ***** For 3 volts
>  x/150k = 12v/3v
> x = (12v/3v)*150K
> x = 600K
> 
> 
> for 2.5 volts
> x/150k = 12v/2.5v
> x = (12v/2.5v)*150k
> x = 720K
> 
> You dont need an exact value. Anything close will do.

-- 
Huw Powell

http://www.humanspeakers.com/audi

http://www.humanthoughts.org/



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