Ned Posted April 26, 2012 Share Posted April 26, 2012 Thats fine to expand further (if you really want to know/waste 5 minutes) all the resistor does is 'eat up' the remaining voltages and turns it into heat. however much current flows through the resistor, flows through the LED. Current is dictated by Current = Voltage/Resistance LEDs have a set forward voltage drop, this does not change If you have a 9V battery, and a LED with a forward voltage drop of 2.5V, you need to 'eat up' (9-2.5=) 6.5V with a resistor. If you want the LED to run at 25mA, you need to calculate what that resistor should be, so resistor value = voltage/current, 6.5V / 0.025A = 260 Ohm The problem with batteries is, that if you now use a different battery, of 10.2V (or whatever it may be) you end up with more current because 10.2 supply - 2.5 forward voltage drop = 7.7 V to 'eat up' by the resistor. So with a 260 Ohm resistor, you have current = voltage / resistance so 7.7 / 260 = 29.6mA instead of 25 so the brightness changes as well and you could blow up LEDs if you aren't careful Quote Link to comment Share on other sites More sharing options...
slacker.cam Posted April 26, 2012 Share Posted April 26, 2012 Ned, you're overcomplicating it. Just bang it together how I suggested and adjust resistor values to get the brightnesses you want. Quote Link to comment Share on other sites More sharing options...
Ned Posted April 26, 2012 Share Posted April 26, 2012 yes, you are correct kind sir, but if this was going to be used daily for a long time, the extra time spend on some LM317s would have been worth while... but yeah, for a 3 minute demonstration of some sorts, it's too complicated Quote Link to comment Share on other sites More sharing options...
cubastreet Posted April 26, 2012 Share Posted April 26, 2012 If you want them all to appear the same brightness, it would pay to use trimpots on at least two of the LEDs. Saves a lot of dicking around with different resistor values. Quote Link to comment Share on other sites More sharing options...
lowlancer Posted April 26, 2012 Author Share Posted April 26, 2012 Having a mare with this. Wired it all up but they were super super dim. So went back to jaycar and got the brightest LEDs they have ($$$$). But still super dim. I feel I may have fucked the resistors up. If I need a 200 ohm resistor, is that "200k"? Or does that ended up being like 100 times too much? Quote Link to comment Share on other sites More sharing options...
Brock-Lee Posted April 26, 2012 Share Posted April 26, 2012 1000 Times Quote Link to comment Share on other sites More sharing options...
Beaver Posted April 26, 2012 Share Posted April 26, 2012 k = kilo = thousand times, ie 200k = 200,000 edit, beaten Quote Link to comment Share on other sites More sharing options...
lowlancer Posted April 26, 2012 Author Share Posted April 26, 2012 Mother fuck Quote Link to comment Share on other sites More sharing options...
Simon Posted April 26, 2012 Share Posted April 26, 2012 Ask the Jaycar guys! Quote Link to comment Share on other sites More sharing options...
Ned Posted April 26, 2012 Share Posted April 26, 2012 the way they will likely write it is 200R (they don't use Ohm at Jaycar i believe) Quote Link to comment Share on other sites More sharing options...
Toucan Posted April 26, 2012 Share Posted April 26, 2012 Eliot is Jaycar Quote Link to comment Share on other sites More sharing options...
lowlancer Posted April 27, 2012 Author Share Posted April 27, 2012 Shit me that was an intense couple days. Got it finished a bit late but managed to sneak into the critique without anyone noticed. Went last, got zero negative remarks Spent $200 on this fucking thing though. Damn crafts/my ineptitude. Cheers HEAPS guys Quote Link to comment Share on other sites More sharing options...
Beaver Posted April 27, 2012 Share Posted April 27, 2012 aye? $200 on 3 leds, some resistors and a battery? Quote Link to comment Share on other sites More sharing options...
lowlancer Posted April 27, 2012 Author Share Posted April 27, 2012 lol 24 LEDs (up to $7.50 each), a fuckton of resistors and a few batteries, plus wire, foamboard ($37) etc Quote Link to comment Share on other sites More sharing options...
Ned Posted April 27, 2012 Share Posted April 27, 2012 giz pics of what you made please Quote Link to comment Share on other sites More sharing options...
lowlancer Posted April 27, 2012 Author Share Posted April 27, 2012 Are on uni computer. Will chuck em up tomorrow May I add I didn't use 24 LEDs making it, only 9, but burned heaps out due to rushing like a fuckwit. Quote Link to comment Share on other sites More sharing options...
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