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Author Topic: Beginner question: Arduino & External Power Supply  (Read 2249 times)
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Monterrey, N.L. México
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Hey Robert,

Those LED's are great!

What I'm using for my model R.R. signal LED's are up to 6 of these 330 ohm bussed wired resistors in a 16-pin DIP package. Pin 16 is common to 15 resistors and I connect them to either +5 or 0. Of course I must use all pins in a DIP as either pulldup or pulldown.

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Billy     http://www.z-world.com/operations/gbremer/

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whatever remains, however improbable, must be

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Yes, folks have found all kinds of neat uses for the LED strip, including as the elements of 7 segment displays.
These LED strips are controlled by TPIC6B595 on an arduino-based board I designed.
http://swimmeetkeeper.com/id2.html
This one has 4 digits.
http://www.crossroadsfencing.com/BobuinoRev17/SwimPaceDisplayBoard.JPG
This one will do 96 segments (thinking 12 digits)


* 12_digit_driver_board.jpg (673 KB, 1250x1237 - viewed 7 times.)
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Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

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Hi peej,  smiley

The following quote is from the URL link further below. It is for regular diodes but this should also apply to LED's. Current will always 'seek' the least resistance path and since it is hard to find identical diodes (or LED's) it will choose one of them and start the following process.

It works like an endless cycle which ends up with only one diode conducting or broken down. The more current, the more heat; the more HEAT, the more CURRENT, and so on. If you get lucky with well matched LED's and nothing happens, you will at least have one LED brighter than the others.

Interesting.  That's something I would never have figured out on my own, but I'll be sure to keep it in mind.  Thanks!
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Ah, that's a lot simpler.
You can buy LED strips that are powered from 12V, with built in resistor & everything.
All you need is a buffer chip like ULN2803 to control the ground to turn them on & off.

https://www.adafruit.com/products/357

Ah yes, I was considering the strip as well.  I will probably start to look at those if I get more advanced; I'm really interested now in learning the basics of electronics without relying too much on ICs to do the work for me (even though I'm sure they're easier and designed for the task).  This was, for example, my first transistor use. smiley 
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Sometimes a single transistor or two (and associated resistors) is all you need.
For example, on this board (in various stages of construction) I used 4 transistors and 11 resistors to control 4 strings of 5 LEDs each, 1 string of 3 LEDs, 1 LED, and to invert a signal.
A ULN2003 or 7406 with 4 resistors would have done the same. I've had the transistors since 1983 or '84, little drawerful of them, and decided I was finally going to use them for something, so I did.


* Extension_light.jpg (81.1 KB, 960x720 - viewed 9 times.)

* Extension CCAs.jpg (1338.99 KB, 2612x1671 - viewed 7 times.)
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Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

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I've had the transistors since 1983 or '84, little drawerful of them, and decided I was finally going to use them for something, so I did.

Ha, ha, ha! I also bought '2 many' 2N2222's (near 100) in the mid 80's which I still keep in a little drawer, but I never got to use them. And that's 2 many 2's and 2 many transistors. I'll have to find some use for them one of these days.  smiley-lol
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Billy     http://www.z-world.com/operations/gbremer/

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My dad gave these to me when I was in college.
Always did op-amps and higher level logic design, never had a project to work these into.
Can't even find a datasheet on them!
They seem to work well enough for driving strings of LEDs tho.
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Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

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Sometimes a single transistor or two (and associated resistors) is all you need.
For example, on this board (in various stages of construction) I used 4 transistors and 11 resistors to control 4 strings of 5 LEDs each, 1 string of 3 LEDs, 1 LED, and to invert a signal.
A ULN2003 or 7406 with 4 resistors would have done the same. I've had the transistors since 1983 or '84, little drawerful of them, and decided I was finally going to use them for something, so I did.

Well that's pretty close to what I'm doing.  Reassuring to hear I'm on the right track.
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