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NicD
01-08-2007, 04:03 AM
Just about to buy a stack of resistors for annunicator LEDs (B737) and I'm after some advice on what size resistor would be best to get to give a realistic level of brightness. We're using 5v power supply with 20mA for the LEDs...

thanks!

Olympic260
01-08-2007, 04:53 AM
Take a look here

http://www.kpsec.freeuk.com/components/led.htm

It explains how the resistor can be calculated very easily.

Hope it helps

Chris

Bob Reed
01-08-2007, 12:31 PM
Hey NicD. I am using a 330ohm resistor on every led. My leds are 3 volt max and I am feeding them with 5volts from a computer power supply. Reading at the led, with my meter, is right around 3 volts. Been doing it his way for some time with no problems. My leds are in wired in parallel.

Matt Olieman
01-08-2007, 12:36 PM
Take a look here

http://www.kpsec.freeuk.com/components/led.htm

It explains how the resistor can be calculated very easily.

Hope it helps

Chris

Excellent reference Chris.... Thanks :)

brianwilliamson
01-08-2007, 12:51 PM
Here is another link that is quite useful:
http://metku.net/index.html?sect=view&n=1&path=mods/ledcalc/index_eng

Personally I do not use resistors at all. It is too much work installing them !
I use a regulated power supply with a potentiometer to vary the voltage to suit the intensity required. I actually use a couple of power supplies, one at 3.5 volts for the bright leds, and a 2.1 volt supply for the lesser leds on the backlit switches. If you connect up an external potentiometer in parallel to the one that sets your voltage in the power supply, you then can vary the intensity of all your leds down and actally turn them off.
Cheers..............Brian W.

Matt Olieman
01-08-2007, 01:03 PM
[quote=brianwilliamson;7596]Here is another link that is quite useful:
http://metku.net/index.html?sect=view&n=1&path=mods/ledcalc/index_eng
quote]

WOW... that's impressive. We need to stick this in our "Builders Links"

wollo
01-08-2007, 01:13 PM
Brian, Could you show me how you incorporate the pots into the circuit?

brianwilliamson
01-08-2007, 01:49 PM
OK I will try to explain. Hard to do without being able post a picture and a circuit diagram !
Basically I use a kit to build a variable power supply, which is fairly simple and available at most electronic shops. In the setup they have a variable pot to set whatever voltage you need between 1 to 30 volts. All you need to do is connect another pot in parallel to the one in the kit and run a legth of 2 wires with that external pot connected to the one in the power supply and then set the maximum voltage you require. The external pot is then used to vary the voltage downwards.
Hope this helps.....................Brian W

NicD
01-08-2007, 06:00 PM
Thanks for the advice guys - very useful info.