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How can I drop 9 volts to 1.5-3 volts to light up a LED? Answered

Im working on a project that uses 9 volts on all the parts but the LED's What should I do?

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Grathio (author)2009-08-03

To figure out what resistor you need, use the calculator link here.

You're probably looking at something like a 220 ohm resistor for a white LED, 270 ohm for a blue LED, and 330 ohms for a red LED.

(These numbers are based on typical LED specs. Uee the calculator with your LED to figure out the right one.)

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west49rules (author)Grathio2009-08-04

Ok, Im using a white LED and due to the sortage of parts a 330 ohm resistor. But when I hook it all up and check the voltage out of the resistor the voltage is still 9volts 0.o? Resistors drop curent not voltage right???

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steveastrouk (author)west49rules2009-08-04

No, you need to put a load on the resistor. Resistor drop nothing unless there is a current flowing in them.

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ejp1087 (author)2009-08-03

You should be able to use 9V and be just fine. Add a potentiometer after the LED and use that to set the current that you want the LED to be driven at. If you really want to use 3V, that can be done very simply using a potentiometer. Have your 9V go in the left or right pin of the pot. and have the other side grounded. Adjust the pot. until you get 3V at the center pin. I would recommend using a large (10kOhm or higher) pot and sending the 3V through an op amp used as a voltage follower. Another option that I just used for a project of mine is to use and NPN transistor to make a constant current source. My post is getting long so let me know if you want the info on the constant current source or if you have any questions about the other options.

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DIY Dave (author)2009-08-03
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bellinghammakerspace (author)2009-08-03

The easy way is to add two more LED's. Then it will work really well.

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