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Driving RGB LEDs for 16x16

Discussion in 'LEDs and Optoelectronics' started by focalpointLD, Feb 21, 2012.

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  1. focalpointLD


    Feb 21, 2012
    Hello all! New member looking for some LED driving tips.
    I am currently building a 16x16 RGB LED Matrix. Pretty revolutionary, huh?

    I have a decent grasp on the schematic and the control circuitry. I am using Piranha RGB Common-Anode LEDs (30mA If), wired to act as (4) 8x8 RGB Matrices (2x2). For control, I am using 74HC595 Shift Registers, 4 for the rows and 12 for the rgb columns. The SR's would be daisy chained together with serial data/clock from an Arduino Mega2560.

    My question involves driving the LEDs. Since I am not at all expecting my IC's or the Arduino to sink enough current to drive the LEDs, am I able to use an NPN like the 2N5306 per row pin? Would I have to use a separate power supply? I know there are several ways to go about this, but I've already decided for programming purposes to use the 74HC595s, I am just concerned about current and brightness. I could be swayed if there is the perfect IC out there without having to start the programming from scratch.

    Thank you in advance for your thoughts. Let me know if I can clarify anything.

  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Because you'll be multiplexing the LEDs, the average current will be 1/(number of columns) of the value that each output can supply. If this is not bright enough, you will need both row and column drivers.

    One option is to use line drivers to drive your rows as they are capable of much higher outputs than normal gates.

    I see no particular reason why you'd need a different power supply for the LEDs.
  3. focalpointLD


    Feb 21, 2012
    Thanks Steve, that's helpful to know. I am steadily being moved away from the '595s, though I could still use them with beefy PNPs. It seems like a 16-bit serial-shifting LED driver is out there, the MBI5026. Finding it is the hard part...
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