Forum Rule: Always post complete source code & details to reproduce any issue!
Results 1 to 10 of 10

Thread: Can't change 7 segment display

  1. #1
    Junior Member
    Join Date
    Aug 2019
    Posts
    17

    Can't change 7 segment display

    I can get the MAX7219 to initially put numbers on the 7 seg digits, but if I change any value it either turns completely off or completely on (all lights lit 8.8.8.8.8.
    I tried to make a timer that counts seconds, but it turned off, then on, then off, etc. every second.
    There must be something to do besides calling setDigit.
    Where can I look for an example?

  2. #2
    Senior Member PaulStoffregen's Avatar
    Join Date
    Nov 2012
    Posts
    25,206
    Quote Originally Posted by jsureke View Post
    Where can I look for an example?
    In Arduino, click File > Examples > LedControl > LCDemo7Segment

  3. #3
    Junior Member
    Join Date
    Aug 2019
    Posts
    17
    That doesn't even work. It starts working but it doesn't show all the changes and it doesn't loop a second time. I must have faulty components.

  4. #4
    Senior Member
    Join Date
    Apr 2014
    Location
    Germany
    Posts
    9,386
    Quite possible that it is just a problem with the connections.
    If we had a photo, we could take a look

  5. #5
    Junior Member
    Join Date
    Aug 2019
    Posts
    17
    Quote Originally Posted by Frank B View Post
    a problem with the connections
    I just learned that the chip is really finiky.

    Quote Originally Posted by Frank B View Post
    a problem with the connections.If we had a photo, we could take a look
    This prototype isn't the best looking solder job. I'm just going to start over.

  6. #6
    Senior Member PaulStoffregen's Avatar
    Join Date
    Nov 2012
    Posts
    25,206
    Which Teensy are you using? (if I were to dig out my MAX7219, which one should I test....)

  7. #7
    Junior Member
    Join Date
    Aug 2019
    Posts
    17
    Quote Originally Posted by PaulStoffregen View Post
    Which Teensy are you using?
    I have a Teensy 3.5 and an Arduino Mega. Multiple boards, multiple sketches, alll with the same results, so it has to be the hardware.
    I do know that I didn't use the capacitors on the 5v that some people say are needed, so I'm scrapping all of this and starting over, but I'm using a socket this time, so I don't kill my chip. Not that they are all that expensive, but waiting on delivery is a pain.

  8. #8
    Senior Member PaulStoffregen's Avatar
    Join Date
    Nov 2012
    Posts
    25,206
    I found that old MAX7219 test board, plugged in a Teensy 4.1, and ran the LCDemo7Segment example.

    It seems to work fine...

    Click image for larger version. 

Name:	ledcontrol.jpg 
Views:	28 
Size:	74.9 KB 
ID:	22802

  9. #9
    Senior Member PaulStoffregen's Avatar
    Join Date
    Nov 2012
    Posts
    25,206
    Quote Originally Posted by jsureke View Post
    I have a Teensy 3.5 and an Arduino Mega. Multiple boards, multiple sketches, alll with the same results, so it has to be the hardware.
    Yup, probably hardware.

    Since it was still on my workbench, I plugged in a Teensy 3.5 just to make sure.

    Click image for larger version. 

Name:	ledcontrol2.jpg 
Views:	34 
Size:	75.8 KB 
ID:	22803

    On this test board the MAX7219 runs from VIN (5V). There are only 5 wires between the MAX7219 and Teensy: 5V, GND, and 3 signals. The MAX7219 seems to do fine with the 3.3V signals when running from only 5V.

  10. #10
    Senior Member+ defragster's Avatar
    Join Date
    Feb 2015
    Posts
    15,256
    I just got one of these :: protosupplies.com/product/max7219-8-digit-7-segment-socketed-red-display-module/
    Click image for larger version. 

Name:	MAX7219-8-Digit-7-Seg-Red-Display-Module-Socketed.jpg 
Views:	26 
Size:	338.9 KB 
ID:	22804

    Plugged into a T_4.1 it is working with :: ...\hardware\teensy\avr\libraries\LedControl\examp les\LCDemo7Segment\LCDemo7Segment.ino

    Had to extend the running digits to cover all 7 - but it is working. Also 5V VIN and data/control lines from 3.3V T_4.1.

Tags for this Thread

Posting Permissions

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