Forum Rule: Always post complete source code & details to reproduce any issue!
Results 1 to 7 of 7

Thread: Max 7219 pins on 3.6

  1. #1

    Max 7219 pins on 3.6

    I'm biting the bullet and moving to the MAX 7219 for LEDs. Two questions, please:

    1. Can they be on any pins?
    2. Could I achieve the same effect wiring a matrix up to 16 PWM pins? (assuming yes) would it be performant as I have a load of other stuff running off that 3.6.

    Thanks

  2. #2

  3. #3
    Thanks I read that. I'm still not sure if I can use any Teensy pins.

  4. #4
    This is what I have so far. It seems like it should work imagining each separate LED for the RGB CA.
    Click image for larger version. 

Name:	ledmatrix.jpg 
Views:	48 
Size:	77.5 KB 
ID:	12888
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	ledmatrix.png 
Views:	42 
Size:	78.6 KB 
ID:	12887  
    Last edited by alialiali; 02-08-2018 at 10:27 PM. Reason: Decent res schematic

  5. #5
    Senior Member PaulStoffregen's Avatar
    Join Date
    Nov 2012
    Posts
    20,676
    Quote Originally Posted by alialiali View Post
    I'm still not sure if I can use any Teensy pins.
    If using that lib, any digital pins may be used.


    Could I achieve the same effect wiring a matrix up to 16 PWM pins?
    No, not directly.

    The MAX7219 gives you current limiting which is normally done by adding a resistor in series with the LED. It also gives you higher current. If the LED is on for 1/8th of the time, it needs ~8X current during that on time to appear as the same brightness.

    Even if you did add transistors and resistors, something to consider is the danger of 8X current if your software stops in any way which leaves one group of 8 LEDs driven continuously (rather than 1/8th duty cycle). With the MAX7219 chip implementing this in hardware, the risk of damage to LEDs from software errors is virtually zero. If you build a circuit to directly drive ~160 mA current into an LEDs, all sorts of "learning experience" problems can destroy your LEDs.

    This is why the MAX7219 works so well, especially for hobbyist electronics.

  6. #6
    Thanks Paul.

  7. #7
    For anyone who cares, my schematic above doesn't really work. My problem is the blue LEDs. If I increase my RSET resistor to a value that is manageable by the 500mA I have available (32 RGB LEDs), then my blue LEDs won't light. If I reduce it, then I just don't seem to have enough juice and all hell breaks loose. I wish I could test more, but I really have to move on.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •