# DIYstompboxes.com

## Projects => Beginner Project => Topic started by: gnort_2 on July 10, 2013, 12:06:22 AM

Title: Led tutorial or help
Post by: gnort_2 on July 10, 2013, 12:06:22 AM
Time to buy an led and hook it up to my booster pedal.
How do LEDs work?
How are they rated?
How do I know what resistor to use?
Are different colored ones different internally? Or just a different color casing?
How can I test all of this?

Thanks
(Still learning to crawl)
Title: Re: Led tutorial or help
Post by: duck_arse on July 10, 2013, 09:30:32 AM
how they work? they are semicondutor junctions, etc etc. the experts are needed here. different materials internal produce different light colour external.

they are usually rated by their light output; how much of it they produce. also rated by forward voltage, light output colour, wavelength, lens dispersion, etc. get some data sheets, look through them.

you know what resistor to use by subtracting the led forward voltage, which might be 1V6, from your supply voltage, which might be 9V. then you pick a forward current, lesss than the max specified in the data sheet, less than will blind all the neighbours, and a bit less than will drain your battery (we'll assume) in an hour, so lets say 1mA. then you do ohm's law, R=V/I = (9 - 1V6)/0.001 = ? ohms.

this value resistor then limits the current by dropping a voltage, and the led doesn't self distruct. and that's how you test them. buy some leds, and some resistors, and a breadboard, and away you go.
Title: Re: Led tutorial or help
Post by: gnort_2 on July 10, 2013, 10:00:24 AM
What's does 1v6 mean?
Title: Re: Led tutorial or help
Post by: duck_arse on July 10, 2013, 10:14:49 AM
1V6 means 1.6 Volts. many years ago, engineer types decided to replace the decimal point, when it occured, with the multiplier, in this case V for volts. this cut down on strings of '0.000" and typo errors in magazines. supposedly.

1V6 is also the voltage you might read across a red led when lit, with proper series resistor fitted. this is the forward voltage referred to in the data sheets.
Title: Re: Led tutorial or help
Post by: Jdansti on July 10, 2013, 12:11:10 PM
A general safe rule of thumb would be to use at least a 680R (680Ω) resistor for most LEDs. 1.4K seems to be popular. The lower you go, the brighter the LED, but the risk that you'll burn it out is higher.

Someone on the forum, I think deadastronaut or Mark Hammer, built an LED test box with multiple resistors so he could quickly see how bright an LED would be with a given resistor.

You can do the calcs that duck gave you to start with as a minimum value resistor, but I'd have some larger values handy in case you think the minimum would be blinding. After a while, you'll learn what values you prefer.

Edit: premature post button activation. ;)
Title: Re: Led tutorial or help
Post by: gnort_2 on July 10, 2013, 03:23:52 PM
R=(Vs - Vf)/ If

I think Vs is the voltage reading were the led gets its power

Is Vf the voltage rating on the led package?
Title: Re: Led tutorial or help
Post by: Jdansti on July 10, 2013, 05:14:34 PM
R=(Vs - Vf)/ If

I think Vs is the voltage reading were the led gets its power

Is Vf the voltage rating on the led package?

Yes. Vf is the "forward voltage" of the LED.  This is the voltage at which the LED turns on.  If is the current rating for the LED.
Title: Re: Led tutorial or help
Post by: gnort_2 on July 10, 2013, 05:31:57 PM
Thanks again, I'm gonna get this stuff yet...
Title: Re: Led tutorial or help
Post by: aron on July 10, 2013, 08:36:44 PM
WaitAminute - first off congratulations on getting your pedal to work, but come on!!!!! There is a document that explains a LOT of what you ask:
http://www.diystompboxes.com/wiki/index.php?title=DIY_FAQ

It's on the top - the DIY FAQ. Please check it out.  ;)