# Led's In Fretboard

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im putting 10 LEDs in my fret boared powered by a 9V battery, 12mA DC Forward Current rating and 3.5 LED voltage drop. what size resistor do i need for each LED

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http://projectguitar.ibforums.com/index.ph...l=led+fretboard

There's quite a ton of info in that thread, I'm sure you'll find the answer to your question as well as questions you didn't even know you had in there.

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http://projectguitar.ibforums.com/index.ph...l=led+fretboard

There's quite a ton of info in that thread, I'm sure you'll find the answer to your question as well as questions you didn't even know you had in there.

iv allread been on this but i dont under stand how to do figure it out im using the same LED's as him but hes using 6 AA batterys where as im using a 9V battery so i need bigger resitors but i dont know wich ones

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PM Dave. Hes the guy that started the tutorial.

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i used 470 ohm on my fretboard project. i like them nice and bright.

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6 AAs will last much longer than a single 9V though.

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Look at it as a math exam question:

Calculate the resistance and wattage of the series resistor required to drive an LED with a forward voltage of 3.5 volts at 12mA from a 9 volt supply - show your work

9-3.5=5.5 (supply voltage minus LED forward voltage equals resistor voltage)

5.5/.012=458.33... (voltage divided by required amperage equals resistance)

The nearest larger standard 5% value is 470 ohms - assume 470 ohms for power calculation.

(5.5^2)/470=.06436.... ( voltage squared divided by resistance =power)

Lowest easily sourced power rating is 1/8 watt (over double the calculated power), so specify a 470 ohm 5% 1/8 watt resistor.

Sounds like ansil's pretty good at this, or at least he owns a pocket calculator.

BTW, feylya makes a good point - 6 AAs will last about 5 - 10 times as long as a 9 volt.

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c'mon man, 6AA's in series produces 9 volts(each one produces 1.5volts...link them in series and you add the voltages). that's high school stuff.

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Look at it as a math exam question:

Calculate the resistance and wattage of the series resistor required to drive an LED with a forward voltage of 3.5 volts at 12mA from a 9 volt supply - show your work

9-3.5=5.5 (supply voltage minus LED forward voltage equals resistor voltage)

5.5/.012=458.33... (voltage divided by required amperage equals resistance)

The nearest larger standard 5% value is 470 ohms - assume 470 ohms for power calculation.

(5.5^2)/470=.06436.... ( voltage squared divided by resistance =power)

Lowest easily sourced power rating is 1/8 watt (over double the calculated power), so specify a 470 ohm 5% 1/8 watt resistor.

Sounds like ansil's pretty good at this, or at least he owns a pocket calculator.

BTW, feylya makes a good point - 6 AAs will last about 5 - 10 times as long as a 9 volt.

i accidently bought 1/4 watt resistors how much will this affect the will they be brighter or dimmer

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No difference whatsoever - they'll just take up more room. If you can fit 'em in there, you've got no other issues.

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No difference whatsoever - they'll just take up more room. If you can fit 'em in there, you've got no other issues.

kk thanks

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c'mon man, 6AA's in series produces 9 volts(each one produces 1.5volts...link them in series and you add the voltages). that's high school stuff.

Are you denying that the AA's will last longer? Because despite the fact that they offer the same voltage, the AA's have a MUCH higher power capacity. Energizer's 9V batteries have a 625mAH capacity (meaning they can supply 625 mA current for 1 hour, or 1 A for .625 hours, or any set of milliamps/hours that multiply to give 625. Energizer's AA's, on the other hand, have a 2650mAH capacity, giving just over four times the runtime.

You can find this information if you go to www.energizer.com and look in the "technical info" section.

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No, no, no. He thought he needed bigger resistors for 6AA's as opposed to a 9 volt. This just isn't true, since the forward voltage is the same and the draw of the LED's is the same, the resistors would be the same value.

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No, no, no. He thought he needed bigger resistors for 6AA's as opposed to a 9 volt. This just isn't true, since the forward voltage is the same and the draw of the LED's is  the same, the resistors would be the same value.

Ok, good

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