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I've got an RGB led strip I'm trying to control. It's a 12v, 4 pin strip. Pin layout seems rather odd to me as 1 pin takes 12v of power and 3 pins (that go to ground) control the colors. In other words, the LED colors are controlled by limiting outgoing voltage.

Led Strip

  • White- +12v
  • Green- Green in negative voltage
  • Red - Red in negative voltage
  • Blue - Blue in negative voltage

I've already made a similar setup that uses n-channel MOSFETS (or at least I think that's what they are) between the colored cables and the ground and Arduino power the MOSFET gates as necessary.

So my question is: is it possible to hook these LEDs up directly to arduino and control the negative voltage without aditional electronics?

As a slightly off topic question: Is there a specific name for elements that are controlled with negative voltages.


By the way, I'm using Arduino nano, although I don't think it is relevant at this point and I've got Mega and Uno aswell if needed.

  • It seemed weird to me too, at first. But you'll find out it actually makes it a lot easier to connect. Switching the cathode side only requires an n-channel transistor/mosfet, which you can drive directly from 5v arduino pins. Switching the anode side would require additional components since the transistor/mosfets would require 12v signals. – Gerben Dec 15 '15 at 16:35
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No, it's not possible, since the voltages and currents involved (12V) are too high. It will damage your board.

Your arrangement with N-channel MOSFETs is the correct arrangement.

By the way, you are not working with "negative" voltages at all - it's all positive - you just happen to be between the "load" and ground.

This is called a Low Side Switch since it is on the "low" (i.e., between the load and ground) side of the circuit.

The LEDs you have are in an arrangement called Common Anode in that the anodes (+ pins) of the LEDs are all tied together (common) and you control the cathode (- pins) of the LEDs. It means you can use cheap N-channel MOSFETs that are (as you have seen) easy to control with a microcontroller. The other arrangement, Common Cathode, where all the cathodes (- pins) are tied together and you switch the power to the anodes (+ pins) requires P-channel MOSFETs and N-channel MOSFETs to switch the P-channel MOSFETs, which increases costs.

  • Just for the reference If I used 5v LEDs would it be possible then? – Zero Dec 15 '15 at 15:24
  • If you used 5V LEDs and the total current for all the LEDs on one colour channel was below around 20mA then yes it would be possible. – Majenko Dec 15 '15 at 15:25
  • I'm still far from understanding the limits of arduino, but. I just checked the leds. They are just under 4mA/channel. Wouldn't that work with VIN pin powered arduino? – Zero Dec 15 '15 at 15:31
  • Then if they are 5V LEDs you can run around 5 channels in parallel without any extra hardware. Any more than that and you will need the MOSFETs regardless to handle the extra current. – Majenko Dec 15 '15 at 15:33
  • It doesn't have to be MOSFETs, a bog-standard cheap NPN BC547 or similar would be fine. – Mark Williams Dec 15 '15 at 15:55

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