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Another LED Question Answered

Hey guys, I want to make a sign with LEDs for my girlfriend(A hello kitty one). I am new at this so I have a quick question. I don't even know if this is possible, but I want to connect 32 white 5mm LED's in parallel and 32 red 3mm in another parallel and run them both off the same power. What sort of power supply do you guys recommend? I was hoping something like USB, but I dont know if that will work. Maybe a 9V battery? And if any of you know a website that sells LEDs t hat will ship to a military address in Iraq, let me know! I will deffiantly make this into an Instructable when I know what I am doing. Any ideas or help would be awesome. Thanks guys. Andrew B.


Well ok then. If I use a 9v battery for one white LED I need a 270 Ohm resistor between the postive power and the LED. So.... I can just put one 270 Ohm resistor between each white LED and the power in the parallel? Likewise with the red but with a 390 Ohm resistor? A little help?

A more efficient way would be to put 2 whites in series with a 150 ohm resistor and put 5 red leds in series with a 27 ohm resistor in series put a those sets in parallel will use less resistors and be more efficient

Awesome idea, Thanks for the input, I am going to get the stuff I need and start this bad boy. Thanks!

I think I am going to give up on the USB deal, seems to be to hard and she will probably not have it on all the time anyway, I think I am going to go with a nine volt battery. How many mA does one of those bad boys put out?

well, I have a solution that could work off of usb but somebody has to check me onthis cause it might not work cause of some cray voltage drop thingy (but I don't think so) You will have 32 sets of LEDs A set of LEDs consists of : a red led, a white led, and a 15 ohm resistor. Put the red and the white in series (I think this'll work, I don't see why) and the resistor in series with that. The resistor will limit it to 15mA. All together the circuit would take 480mA, and a usb port (high power) outputs 500mA, so you're pushing it...

Would it be better to put My LEDs in series rather then Parallel? Wouldn't it take a large Voltage to run that? My idea with the USB would be she could keep it pluged into her computer or use a USB wall charger and plug it into that if she wanted it away from her desk.


9 years ago

At 64 LEDs, and "about" 20mA each, you're looking for about a 1.5A supply (you might get by with 1A, putting some of your red LEDs in series.) In general, it's not a great idea to parallel a lot of LEDs with a single resistor; the ideal situation has one resistor for each LED. A 5V supply would be pretty good; it'll light two red LEDs in series or a white LED, and it's a common voltage... Do try to find a "regulated" supply (see this Unregulated supply tutorial at SparkFun! )

sorry, i dont order many LED's, but usb only puts out 5v, 9v puts out(you guessed it) 9v, if you can, try like an outlet plug thigy. just strip(hey this is pg-13!) the wires and add resistors i guess, correct all my dumb mistakes anyone?(also, plz excuse my horrible joke-like-things.)