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I need to control about 6 RGB Led Strips from an Arduino Board. The problem is that i need 3 PWM outputs for each led strip, but each will have probably the same colors. I was wondering if i could put two strips receiving a signal from the same PWM output, then i would have to use half the PWM outputs but send the same signal for each pair of strips.

The scheme i found is this one:

arduino schematic

And what i want is something like this: enter image description here

Is this possible? What should i modify to make it work?

Thanks in advance.

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1 Answer 1

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You have few options:

  1. do as you represented in the drawing: it should work, as I expect the transistors to not load too much the input.

  2. add a logic buffer inbetween the arduino and the driver stage

  3. use other pins from the arduino for driving the additional strips and bitbang the PWM, instead of using the HW blocks

Whether the solution you propose (1) will work or not depends entirely on the max current that each PWM pin can output vs the total load from the 3 transistors it will have to drive.

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  • That was very helpful, i was afraid about this current thing, but apparently each 1 meter uses 20mA, and a pin can output 40mA, so 2 strips would be the perfect amount.
    – George Rappel
    Commented Sep 23, 2015 at 22:04
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    Did you check that 20mA is the Max Value, rather than Typical? You might have some unpleasant surprise, if you take chances and do not plan for the worst case. Same goes for the Arduino/Atmega: is 40mA the Min Value or the Typical? You should match Min from the source vs Max from the drain and confirm that they are compatible.
    – Igor Stoppa
    Commented Sep 23, 2015 at 23:52
  • That's true. But the max that the strip uses is 20mA at full bright, and the typical that arduino provides is 40mA. Since i'm never gonna use it at full bright i think it should work.
    – George Rappel
    Commented Sep 24, 2015 at 1:44
  • 5v with a 220ohm resistor will result in about 20mA of current. Depending on the gain of the transistors and the amount of current the strips use (i.e. depending on their length) 20mA might not be enough to fully saturate the transistor. In that case the leds won't be as bright, and the transistor will get pretty hot. Using MOSFETs will prevent this problem.
    – Gerben
    Commented Sep 24, 2015 at 14:32

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