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

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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

10 years ago

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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papadewey221Grathio

Reply 6 months ago

I am a new B to this site. I am doing something similar. I want to use a 9 volt battery to power lights for an RC car. The led lights use 3 volts at 32ma. Since I am electronically challenged, I hope someone here can give me some idea the resistance I need to accomplish this. Will this also control the current so I don't burn up the lights, they are somewhat expensive. Thanks for the help in advance.

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west49rulesGrathio

Answer 10 years ago

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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steveastroukwest49rules

Answer 10 years ago

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

10 years ago

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

10 years ago

Use a resistor.

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bellinghammakerspace

10 years ago

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