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I'm looking to make a DIY version of Dan Conrad's Spectrabloom. I've got an Arduinio Uno, a piece of code that uses PWM to randomly fade three 1w LEDs (one red, one blue and one green) and a PicoBuck LED driver.

Question is - do I have to have two power supplies? One to power the PicoBuck and one to power the Arduino or can I have them all running off one supply? If the latter - can anyone give me pointers on the way to hook everything up?

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Question is - do I have to have two power supplies?

No, you can use one power supply for both. But you need to make sure, that the LED current is not flowing through the Arduino, since that can kill the Arduino. To do that, you need to connect the power supply to the LED driver and the Arduino in parallel. For example, lets assume you have bought a 5V wallwart/power supply, which is can provide enough current for your whole circuit (and some headroom for further development). Then you can connect the positive lead to the 5V pin of the Arduino and the Vin+ (positive supply voltage) pin of the LED driver. Also connect the negative lead of the power supply to ground on Arduino and Vin- (negative supply voltage) of the LED driver. That way the current for the LEDs comes directly from the power supply and doesn't need to flow through the Arduino, but past it.

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  • Thanks Chris - I have a wallwart + splitter that I intend to run into two dc jacks connected to the Arduino and the LED driver respectively - will this work? – DJM Apr 10 at 10:10
  • Yes, if it has a fitting voltage rating – chrisl Apr 10 at 10:16
  • Yeh, neat - it does. All good. Thanks for your help. – DJM Apr 10 at 15:05
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Three 1 Watt LED could potentially draw 600 mA total, exceeding the maximum draw for the Arduino. Each LED could draw 200 mA, exceeding (by 10x) the draw of a pin driver. So, yes, you need to supply the LEDs separately from the Arduino. Also, that driver is a constant-current driver, at 330 mA per channel. Your LEDs would prefer a constant voltage, chopped by PWM.

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  • I haven't quite understood, why a constant-current driver would be a problem. Isn't that a quite common way to drive LEDs, especially the high powered ones? Or do you mean, that 330mA per LED would be too much? The OP didn't specify, which LEDs he uses. – chrisl Apr 8 at 22:34
  • If constant current is usual, I wasn't aware of it. But yes, I wouldn't choose a supply that could overdrive my devices by 50% if I let the PWM get too high. Murphy is never far away... :) – JRobert Apr 9 at 11:51
  • I know constant current drivers from laser diodes (which electrically are just LEDs). I think they are commonly used in that field, because the current is what actually determines the intensity. Also you can tune the intensity more easy via current, than via voltage because of the (I think exponential) non-linear rise of the diode characteristic. In the end it should not be important, if you use constant current or constant voltage, as long as you don't overload the LED. I think that overload is the important point in your argument. You are right with Murphy. – chrisl Apr 9 at 12:07

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