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Author Topic: hooking up a couple rgb's  (Read 1008 times)
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Hello everyone

Im building one of my first projects and I need it to go as smoothly as possible. I've read some of the material around but still cant help but feel clueless. So I've got to hookup up three RGB LEDs and basically just have them run four different states from my arduino uno. So from what I can gather Im going to need to use a driver. I got a lp5521 three channel driver because it was free. Before I can actually test it I have to write about it so I need some help on how the connection will look. I have no clue if I even have the right driver for the job. Any help I can receive on how to properly connect the three LEDs to the driver and the board would be greatly appreciated. I attached a link to the lp5521 if it helps.

 http://www.ti.com/product/lp5521
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Building a first project with a ball grid array part is a mistake.
Use a more standard part, TLC5490, WS2811, if you want PWM control on all pins.
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Ok I can definitely try and get one of those drivers. One thing I was unable to find out was whether I still need resistors for the LEDs if I'm using a driver
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It depends on the sort of driver. If it says constant current then you don't need resistor's otherwise you do.
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The link you provide also hosts the spec sheet for the driver. These are essential to understand what you can do with a driver. Driver spec sheets often show several examples of schematics as does the one in you link. Sometimes there are even more specific application  notes for demo boards for these drivers. That will tell you what components are needed.
As crossroads has already stated, for a first project a ball grid component is not advisable whatsoever. So...now go find yourself a suitable driver, perhaps in nothing smaller than a TSSOP package as that can still be bad soldered - although that takes some skill. Try to understand the data sheet, google for terminology in the data sheet that you don't understand and then come back if you have questions. There is am awesome world of information out there particularly for LED technology and it's right at your finger tips ;-)
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Thanks for the responses everyone, I just have a question about the TLC5940 that was suggested. It seems that from the connections ice seen online have the three legs of the LEDs hooked up to a seperate output pin of the driver and the long leg is connected to a power supply. Is that right, seems like an odd connection to me.
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Thanks for the responses everyone, I just have a question about the TLC5940 that was suggested. It seems that from the connections ice seen online have the three legs of the LEDs hooked up to a seperate output pin of the driver and the long leg is connected to a power supply. Is that right, seems like an odd connection to me.

That's correct; the TLC5940 "sinks" current as do most LED drivers of its type. Also, as a corollary, your LEDs will only work with this driver if they are common anode (the three colors all share one anode pin) rather than common cathode.
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Ok so looking at some of the possibilities, I'm wondering if someone can tell me if I'm right. I can either program the TLC5940 itself and hook up the LEDs to one driver or I can use three drivers, one for each color in the red green blues (each color leg of the LEDs hooked up to a separate driver. I guess the reason for the latter would be to avoid programming the driver which I don't know if it will be difficult or not.
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What kind of RGB leds are you using (what are the specs - how much current?). Can you provide a link to where you got them?

The TLC5940 has 16 outputs each of which can be used for any color. You don't need three seperate chips.
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planning on using these
http://www.superbrightleds.com/moreinfo/component-leds/rl5-rgb-clear-tricolor-led/298/1225/?utm_source=googlebase&utm_medium=base&utm_content=RL5-RGB-C&utm_campaign=GoogleBaseChild&gclid=CNOliPCbxLgCFQto7AodCSoAdg#customerreview

But if I use one chip wouldn't I have to program the drivers instead of just turning them on from the I/O pins?
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See http://playground.arduino.cc/learning/TLC5940. The TLC5940 itself isn't programmed, but rather you use the Arduino to communicate with it and tell it what to do.

Each TLC5940 will happily drive 5 of your LEDs (16 channels, 5 LEDs * 3 colors = 15, 1 extra channel). And, as the link above shows, you can chain multiple TLC5940s in a chain for many more LEDs.

It's also appropriate to mention that if you're only driving three RGB LEDs that are rated 20ma then you don't need any extra driver at all. See http://forum.arduino.cc/index.php/topic,10008.0.html
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Thank you kind gent smiley
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