b5111987 Posted July 12, 2005 Report Share Posted July 12, 2005 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 Quote Link to comment Share on other sites More sharing options...
StratDudeDan Posted July 12, 2005 Report Share Posted July 12, 2005 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. Quote Link to comment Share on other sites More sharing options...
b5111987 Posted July 12, 2005 Author Report Share Posted July 12, 2005 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 Quote Link to comment Share on other sites More sharing options...
monkey69962000 Posted July 12, 2005 Report Share Posted July 12, 2005 PM Dave. Hes the guy that started the tutorial. Quote Link to comment Share on other sites More sharing options...
ansil Posted July 12, 2005 Report Share Posted July 12, 2005 i used 470 ohm on my fretboard project. i like them nice and bright. Quote Link to comment Share on other sites More sharing options...
feylya Posted July 13, 2005 Report Share Posted July 13, 2005 6 AAs will last much longer than a single 9V though. Quote Link to comment Share on other sites More sharing options...
lovekraft Posted July 13, 2005 Report Share Posted July 13, 2005 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. Quote Link to comment Share on other sites More sharing options...
thegarehanman Posted July 13, 2005 Report Share Posted July 13, 2005 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. Quote Link to comment Share on other sites More sharing options...
b5111987 Posted July 13, 2005 Author Report Share Posted July 13, 2005 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 Quote Link to comment Share on other sites More sharing options...
lovekraft Posted July 13, 2005 Report Share Posted July 13, 2005 No difference whatsoever - they'll just take up more room. If you can fit 'em in there, you've got no other issues. Quote Link to comment Share on other sites More sharing options...
b5111987 Posted July 14, 2005 Author Report Share Posted July 14, 2005 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 Quote Link to comment Share on other sites More sharing options...
jnewman Posted July 15, 2005 Report Share Posted July 15, 2005 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. Quote Link to comment Share on other sites More sharing options...
thegarehanman Posted July 15, 2005 Report Share Posted July 15, 2005 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. Quote Link to comment Share on other sites More sharing options...
jnewman Posted July 15, 2005 Report Share Posted July 15, 2005 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 Quote Link to comment Share on other sites More sharing options...
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