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Old 01-17-2009, 09:15 PM
reno12469 reno12469 is offline
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Default How many LEDs can be put together with 12v dc supply

How many LEDs can i put together with a 12v dc supply. The LEDs are 5MM ultra bright white. They operate on 3.0-3.5Vdc, 20mA. They have a 15-25 degree viewing angle. I also want to split the number of LEDs in half and have them flash back and forth without using PIC.
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Old 01-17-2009, 10:07 PM
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You can put 3 leds in series with a limiting resistor. The total current through the leds and the resistor will be 20mA. You can use as many branches of 3 leds as the power supply can power. What is the maximum current the supply can give you?
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Old 01-18-2009, 02:58 AM
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Default Flashing LED's

Use a 555 chip, circuits abound in AAC, source about 6 strings and sink another 6 strings[ of 3 ea. ]. 3X 3V ea.= 9V leaving 3V to drop 3/.o2=150Ω, .o6W
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Old 01-18-2009, 05:07 AM
reno12469 reno12469 is offline
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its a 12 v battery
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Old 01-18-2009, 05:08 AM
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like car battery or a lil baby battery?
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Old 01-18-2009, 09:09 AM
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Quote:
Originally Posted by Bernard View Post
Use a 555 chip, circuits abound in AAC, source about 6 strings and sink another 6 strings[ of 3 ea. ]. 3X 3V ea.= 9V leaving 3V to drop 3/.o2=150Ω, .o6W
A straight 555 will have some trouble doing this, with 12V its positive output is 10.6VDC, due to the Darlington transistor drivers. There is just not enough voltage left over, so you'd need to reduce the number of LEDs on that side to 2, though it would drive 3 LEDs to ground. There are ways around this, are you interested?



The OP will have to give us a flash rate for me to finish determining the values of the resistors and capacitors.
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File Type: gif 555 LED flasher #3.GIF (2.5 KB, 121 views)
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Old 01-18-2009, 04:48 PM
reno12469 reno12469 is offline
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Its a car battery and i would like each one to flash once in one second.

Last edited by reno12469; 01-18-2009 at 05:00 PM.
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Old 01-18-2009, 04:55 PM
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its a car battery
You can wire up to 1000 LEDS or more as I told you on post #2 on a small car battery.
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Old 01-18-2009, 06:57 PM
reno12469 reno12469 is offline
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You can wire up to 1000 LEDS or more as I told you on post #2 on a small car battery.
Ok. But i want something like this that they flash back and fourth in one sec and using as many of the 5MM LEDs as possible in each one hooked up to the 12 v battery.


LED Strobe.JPG
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Old 01-18-2009, 07:54 PM
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You have to upload the picture somewhere to display it in a post. AAC has good picture forums, or you can do it locally on an attachment. My blog has several tricks and tips for this, this one is what you want.

Here is a schematic that will do what you want. If you choose to add more LEDs just parallel new chains with separate resistors.



You can increase efficiency a bit by making C1 1F, R1 10KΩ, and R2 750KΩ. It will drop the current draw from 10ma to 1ma during the alternate cycle.
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