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Author Topic: Lighting Lots of 1.2v Bulbs...or Bright LEDs  (Read 1456 times)
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If you want to light lots of LEDs at once, then shift registers might be a reasonable solution after all. With the 75HC595 you are limited to about 9mA per LED so as not to exceed the 70mA rating of the chip. If you want more current then that, look at TPIC6B595 shift registers instead.
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For a 5x5 matrix, I'd use a MAX7219 if I didn't want to mess with writing the multiplexing code. Or, to have the Arduino do the multiplexing, five pins to drive the columns, via some small transistors or a ULN2003, and five to drive the rows direct, with an appropriate resistor in each row line.
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Here's the general idea if the LEDs are multiplexed by the Arduino directly. Only one column is turned on at a time. If using the MAX7219 or some such external multiplexer, the LED array is identical, the five rows and five columns would then connect directly to the multiplexer chip, and the resistors and transistors would be eliminated.


* matrix_5x5.png (4.06 KB, 826x539 - viewed 15 times.)
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Hi All,

I've realised this is actually quite an involved project for an electronics newbie!

Wondering if anyone could offer me some electronics help...not specifically Ardunio.

I've got to the point where all I'm trying to do is light a single bulb using a 9v battery. This is working, although the light is very dim.

Heres what I did:

* 9v (Battery) minus 1.25v (Bulb) = 7.75v
* 0.25w (Bulb) = 250ma
* 7.75v divided by 0.25a = 31ohms
* I only had a 33ohm resistor, so 7.75/33 = 0.23a (230ma)

So - I attach the +9v of the battery to one terminal on the bulb holder, ground/negative to the other terminal, with a 33ohmn resistor (Orange/Orange/Black/Gold) in-line.

It just about lights up...in fact only seems to light up when I touch the terminals with my fingers...not sure how this is affecting it.

Worth mentioning I was following this:
http://www.wd5gnr.com/basiccir.htm

Anyways...I accept this is not arduino related. Any help much apprecited!!

Thanks!
Simon.
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You've got the right idea. However, 230mA is a lot of current for an ordinary 9V battery to supply, so probably the battery voltage was dropping significantly below 9V. Ordinary LEDs need much less current than torch (flashlight) bulbs.
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