[simpits-tech] Resistor for LEDs?

[Chris Brace]

Hey cool, 
so far this is very interesting and I actually understand it and will use this 
idea for my panel back lighting too.

My question would be, how do I modify this so that I can control the level of 
brightness. Im thinking either a set day/night switch, or a variable resistor  
but where would I need to put it?

Chris.

> Ahhh, that makes sense...
> 
> Yes on resistor per led or you would have to calculate the ohm value
> over again when ever you add more led to the "bus"
> 
> or as an alternative, if you are using a ATX PSU, it will have a 3.3
> volt output aswell, and if im not mistaken you kan drive 50w (but im
> not
> 100% sure, but the Athlon uses something in this region) from that 3.3
> line, this gives you (acording to this law : P=U*I) 15A, enough to
> drive
> more then 800 leds
> 
> http://www.akasa.co.uk/enhance/atx1125b.gif
> 
> /Stig
> 
> -----Original Message-----
> From: Joseph Fagner [mailto:crease-guard@attbi.com]
> Sent: 23. december 2002 21:35
> To: simpits-tech@simpits.org
> Subject: RE: [simpits-tech] Resistor for LEDs?
> 
> 
> Q2. I understand what you are asking. He wants to know that if he set
> up a power strip (i.e power coming into a bus bar with multiple
> connecting site to feed power to multiple LED's) would he need to have
> a
> resistor for each LED or could he put one resistor between the bus bar
> and power line? I believe you would need to use a resistor for each
> LED, as if you start lighting several LED's, you will be running an
> increasing current through that one resistor as the multiple LED's
> produce an increasing load. If the resistors wattage is rated high
> enough you could probably get away with just one, but I think it would
> be safer to use a 1/8 watt resistor for each LED. 
> 
> Any one disagree? I'm no electronics expert but this is what I plan on
> doing.
> 
> Jay
> 
> -----Original Message-----
> From: simpits-tech-admin@simpits.org
> [mailto:simpits-tech-admin@simpits.org] On Behalf Of Stig Joergensen
> Sent: Monday, December 23, 2002 1:18 PM
> To: simpits-tech@simpits.org
> Subject: RE: [simpits-tech] Resistor for LEDs?
> 
> Mike 
> 
> q1:
> 
> do you know this law: U=R*I that is Voltage = Risistance * Amps
> 
> you need a voltage drop of 5-3.2 = 1.8v and the amps is about 18ma this
> will give you 1.8 = R * 0.018 eg. R = 1.8/0.018 = 100 ohm
> 
> q2: i dont understand what you are asking?
> 
> /Stig
> 
> 
> -----Original Message-----
> From: Mike Williams [mailto:mikewilliams3@comcast.net]
> Sent: 23. december 2002 19:53
> To: simpits-tech@simpits.org
> Subject: [simpits-tech] Resistor for LEDs?
> 
> 
> 
> 
> Going to be using a PC power supply for my LEDs for my pit, using the
> 5v
> line, what
> resistor would I use to bring the voltage and amps down to 3.2v, second
> part
> of the question, if I feed a terminal strip with the 5v line to feed
> all
> the
> lines to the LEDs, (panel backlighting) could I use just one on the
> incoming
> 5v line, or would I use them on all lines from the terminal strip to
> each
> LED, sorry if this question is simple, I'm just not much of an
> electronics
> guy.
> Thanks
> 
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Chris Brace
V(H) +64 4 973-6378
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E chris.brace@paradise.net.nz