# Help a student out

Discussion in 'General Electronics Chat' started by kmeister, Sep 9, 2013.

1. ### kmeister Thread Starter New Member

Sep 9, 2013
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Hi, i'm new to this forum and i need some help to find a specific integrated circuit. Basiclly i've got an RGB LED that is hooked up to an arduino board. the board only have 5 gates and one RGB uses 3 and i need at least 3 RGB LEDs. (buying more arduino boards will be too expensive)

So i need some kind of IC that can switch between several LEDs or sets of LEDs
It needs to have 1 input and then be able to switch between for example 3 outputs (3 different LEDs) Does something like this exists? and purchaseable means?

Aug 17, 2013
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You don't need more than 3 PWM and 3 digital pins for 3 RGB LEDs. Try something like this, but only in 2 dimensions and by using each level for selecting each LED.

PackratKing likes this.
3. ### kmeister Thread Starter New Member

Sep 9, 2013
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Thanks, what are the black component to the side with the big 'N' on it?

Aug 17, 2013
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those are NPN transistors. When a digital pin is high, it sends current to the base of the transistor, which would allow current to pass through its respective LED to ground.

So, you control which of the 3 colors you wish to use and their intensity with 3 PWM pins, and you control which LED with 3 digital pins through the transistors. You loop it, and the LEDs blink so fast that it looks as if they were always on at the same time.

PackratKing likes this.
5. ### WBahn Moderator

Mar 31, 2012
20,228
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You said that one RGB LED uses 3 outputs. Could you describe this RGB LED a bit more fully? What do you need to do to get the different colors?

6. ### kmeister Thread Starter New Member

Sep 9, 2013
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The RGB LED has got 3 input leads 1 common anode. so i need 3 outputs on the arduino board for 1 RGB LED. And we need to somehow switch between the 3 RGB LED's. But when we switch from one LED it needs to keep the color that was appointed to it before we switched LED's.

7. ### WBahn Moderator

Mar 31, 2012
20,228
5,755
I think the thing you are missing is that you aren't going to be keeping the LEDs lit when you switch to other LEDs. They are going to go dark. You will simply rotate between the LEDs fast enough so that, to the human eye and brain, they appear to be continuously lit.

8. ### kmeister Thread Starter New Member

Sep 9, 2013
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No you see i have to be able to change the light level using a range sensor, for EACH RGB LED.

I need to adjust this light level for each individual RGB LED and THEN have them all turned on at the same time.

9. ### THE_RB AAC Fanatic!

Feb 11, 2008
5,435
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Google for "shiftbrite" style RGB LED modules. These run from 5v, and only need 1-3 driver pins from your arduino to run as many RGB LED modules as you like (they connect in a series string on the data pins).

The same basic functionality is available under a number of names from different suppliers.

10. ### WBahn Moderator

Mar 31, 2012
20,228
5,755
Why?

I think you are imposing a false requirement on yourself that is going to force you into a needlessly complex and costly solution.

Using the approach I mentioned you can have a bunch of sensors that each determine the brightness of a bunch of LEDs individually and that all appear to come on at the same time and all appear to be on continuously all at the same time to a human observer.

What facet of your problem demands that they all physically be on at the same time? Why isn't the appearance of being on at the same time good enough?