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LED Matrix Drivers, differences? — Parallax Forums

LED Matrix Drivers, differences?

JedJed Posts: 107
edited 2009-01-31 06:04 in General Discussion
As far as driving an LED matrix, It seems there's more than one way to skin the cat. From what I can tell the most popular chips are either the max7219 or using a shift register like the 74HC595. Can someone tell me why you would want to use one over the other?

Comments

  • ZootZoot Posts: 2,227
    edited 2009-01-30 23:53
    A shift register is not an LED driver, though they are sometimes sorta used that way. A true LED driver generally has features related directly to driving LEDs, such as:

    - setting current for all connected LEDs with a single resistor

    - scanning/matrixing capabilities for driving many LEDs at once from fewer pins (i.e. 16 pins to drive 64 LEDs)

    - shutdown/startup/sleep

    - PWM brightness (either for all LEDs as a set like the 7219 or per LED)

    - depending on model, decoding of HEX characters to 7-segment displays

    - etc.

    Also, '595s differ by model in terms of what they can drive at output. Some will drive 20-50ma on each pin; some only 6ma (less than a Stamp pin). LED drivers are usually only limited in terms of total current through the chip's Vdd and Vss pins, and is often quite high.

    This doesn't mean that using a '595 isn't totally appropriate, for say only 8 leds where you don't mind resistors for each LED and you don't want to keep refreshing the output.

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  • JedJed Posts: 107
    edited 2009-01-31 00:30
    Thank you for the quick response and the info. Which led driver can PWM each led individually? This would be for an 8x8 matrix.
  • ZootZoot Posts: 2,227
    edited 2009-01-31 02:01
    I'm not sure if there is a driver that will do an 8x8 matrix with individual PWM (your scan speed would be so slow you'd get flicker). Drivers I've seen with individual PWM control ususally run somewhere between 8-20 individual LEDs. Do a search at Mouser.com, Digikey.com or Jameco.com for MAXIM drivers -- there are lots of flavors to choose from. Some are SPI, some I2C, etc.

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  • LeonLeon Posts: 7,620
    edited 2009-01-31 06:04
    TI makes a similar chip to the 'HC595 with high-current outputs.

    The XMOS chips will do PWM on each LED in very large arrays:

    www.xmos.com

    They are probably overkill for your application, though.

    Leon

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