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The USB powered LED CD lamp

Step 3Mount the LEDs and the resistors on the CD

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Now, mount the LEDs and resistors. Move your mouse over the yellow boxes to view instructions.

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11 comments

Nov 9, 2011. 4:16 PMcvolckmar says:

I have a challenge here. I have a power source that is 53v DC and I want to use 7 Super bright LEDs. I'm new to electricity and I think that it will blow the LEDs since they run on a few volts each. What size resistors do I need use? And where do I install them? I need to use the 53v source. Please show calculations. THANK YOU in advance =]

May 8, 2012. 2:02 AMno_light says:

add the voltages of the LEDs
subtract from the 53v source
divide with the LED current , most LEDs have 20mA so it is .02 A

so
R=(V1-V2)/.02A

Feb 5, 2010. 11:30 AMtaurusguy88 says:

well i made my usb lamp,
but i connected all the led in series
but the pro is i get a notice on my pc
power serge on usb ...
whts to do with tht ??

Sep 22, 2011. 5:23 AMkresimir says:

you short connected something

Aug 21, 2011. 5:38 PMnodoubtman says:

Hello! : How do you get 68 Ohms resistor ??

So : 7 LEDs 20 mA each, 3.5 V each to run, 5 V usb max.

R = (5 - 3.5) / (0.02 * 7) = 10.71 Ohms near value = 12 Ohms. Which is far away from 68 Ohms resistor.

Can you give me your trick? :)

Have a great day! :)

May 23, 2008. 10:20 AMDrChill says:

Just a suggestion. You may need just one resistor. Just wire it so its between each LED and power. I'm guessing a 1/2 or 1 watt resistor should do the trick... It will save a little solder and 1/2 dozen parts ... Nice job. : )

May 23, 2008. 12:00 PMHandsome-Ryan says:

It is a bad idea to wire LEDs in parallel as you are sugesting.

I'll quote from The Electronics Club:

Connecting several LEDs in parallel with just one resistor shared between them is generally not a good idea.
If the LEDs require slightly different voltages only the lowest voltage LED will light and it may be destroyed by the larger current flowing through it. Although identical LEDs can be successfully connected in parallel with one resistor this rarely offers any useful benefit because resistors are very cheap and the current used is the same as connecting the LEDs individually.

May 24, 2008. 1:41 AMArtificial Intelligence (author) says:

Yeah, I've heard that to, and that's why I didn't do it.

Aug 21, 2011. 8:00 AMnodoubtman says:

Are the led in parallel or series ??

thank you!
CYa!

May 24, 2008. 10:10 PMDrChill says:

"If the LEDs require slightly different voltages -only- the lowest voltage LED will light " No. And how much is 'slightly' anyway ? Is 2v 'slightly' different than 3v ? As long as the resistance is appropriate for each LED and the resistor can handle the load, there's no problem. Since this DIY uses the -same- LEDs, they need the -same- current, so there's no problem. And, as the last line of the quote says,"...and the current used is the same as connecting the LEDs individually." Thats my point. Its the same. It's the same current unless the LEDs -are- different, and if they ARE different then use different resistors, not 7 of the same ... Try it yourself. Its easy to test and see who is right here... I like elegant solutions, not wasting parts, and not scaring people away from simpler solutions without understanding why. If you like wasting parts, I have lots of projects for you to try ... ; )

May 27, 2008. 6:41 AMArtificial Intelligence (author) says:

OK, then do it your way. And what projects could I try to waste parts.

May 28, 2008. 5:26 AMHandsome-Ryan says:

You should post up some instructables of your own. A.I. and I both have posted instructables where we wired circuits for LEDs. Not that simple LED circuits are that challenging but you might be able to demonstrate what conditions are required to use a single resistor safely.

May 28, 2008. 9:23 AMDrChill says:

Thanks for the suggestion. AI's project is a good candidate for using one resistor for all ( not each ) LED. As long as each LED has the same specs, and the resistor is properly sized, it would work. I started playing around with using the PC power supply as a source of power for projects including an LED Lamp.... I'll keep you posted. Regards.

May 26, 2008. 5:14 AMHandsome-Ryan says:

I'm not scaring people off, I'm stating the generally accepted rule of circuit building.

May 26, 2008. 1:47 PMDrChill says:

Sorry. The Electronics club doesn't have it quite right.

Its NOT a generally accepted rule. Its a waste of parts, and there's no logical justification for it.

I will say that as a design rule, simpler is better.

Here's a link that discusses LED wiring more fully and accurately than the Electronics Club.

From circuitry 101:
http://www.theledlight.com/ledcircuits.html

Sep 8, 2010. 6:58 AMdrf009 says:

what is resistor volt?? 250ohm???

Nov 20, 2008. 12:12 PMGuy.Fawkes says:

Wire the LEDs in series, and you definitely need only one resistor. LEDs are current-sensitive; calculate the current from your supply voltage (in this case, 5VDC) through the resistor alone. If you used a 68 ohm resistor, then the current will be about 74ma. 20ma is adequate for most LEDs, so you could increase the resistor to 250 ohms.