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Led limit for arduino
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Re: Led limit for arduino

by GAHorton on Sat May 02, 2009 7:03 pm

what are the values for these components?


westfw wrote:Before this gets TOO tangled, let me point out that if the goal is to light 4 LEDs on a single pin, it may be simpler to use a parallel configuration. You need the transistor in either case, but the parallel config lets you get by without needing to deal with a separate power supply for the LEDs.
Image
http://farm4.static.flickr.com/3664/348 ... 304dd8.jpg
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Re: Led limit for arduino

by westfw on Sat May 02, 2009 9:31 pm

1k should work OK for the base resistor. The other resistors you can calculate using the standard LED resistor equation; in this case the transistor drop is only a fraction of a volt, and can be neglected. So for 2V leds (red/yellow/etc) and 20mA, you'd use about 150 ohms...

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Re: Led limit for arduino

by GAHorton on Mon May 04, 2009 3:59 am

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Re: Led limit for arduino

by westfw on Mon May 04, 2009 11:04 am

Yes. Though even 4 LEDs isn't quite "high power" compared to the motors and lamps that tutorial is talking about. There is also http://www.arduino.cc/playground/upload ... _leds2.jpg
(but it is just as devoid of explanation as my circuit...)

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Re: Led limit for arduino

by GAHorton on Sat May 09, 2009 9:14 pm

well then is this even feasable to do with the arduino with say 20 lights?


the only way i'm thinking it would work is by having the arduino control the flashing and have as many volts as i need being a separate thing.
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Re: Led limit for arduino

by GAHorton on Sat May 09, 2009 9:15 pm

well then is this even feasable to do with the arduino with say 20 lights?


the only way i'm thinking it would work is by having the arduino control the flashing and have as many volts as i need being a separate thing.
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Re: Led limit for arduino

by The_Don125 on Sun May 10, 2009 5:59 pm

You can control 20 LEDs directly off of an Arduino so long as you use resistors to limit current to approximately 2.5mA per LED if running on USB power (to stay within the 100mA limit of USB) or up to 5mA per LED to prevent burning out the ATMega.
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