I have an Arduino Mega set up with an 8x8 led matrix as laid out in this circuito.io project: https://www.circuito.io/static/reply/index.html?solutionId=6013e67aeaa9ed0030f668fb&solutionPath=storage.circuito.io

A screenshot of the wiring diagram

But when I plug in the usb cable, it looks like this:

Most of the LEDs appear to be on in some sort of grid pattern

I'm using the default code supplied by circuito.io (this was just meant to be a "hello world" jumping off point)

When I run the code, some of the leds flicker on and off, but the ones that are on in the image tend to stay on regardless.

  • Did you open a serial monitor and choose an option? The code waits for input over the serial connection. Jan 29, 2021 at 12:32
  • @PeterPaulKiefer Yes I did, I also tried adding an option that would simply clear the screen (to no effect) Jan 29, 2021 at 13:39
  • Some guesses: The module is not correctly wired. Show a picture where I can see the connections, the arduino and the matrix completely then, I could check it for you. - A wire is broken. I think you have checked this already. -- The Module is broken. That's possible!. Have you a second one to try? The chip seems to be replacable. Have you another MAX7219 chip to replace it? -- You could have a typo in the code, by accident: add your code (ino-file; the one you use) to the question. I would check that for you. Jan 29, 2021 at 14:04
  • What happens if you only connect Vcc and GND to the module? Could you post a photo of the underside of the module? It might be a bad solder connection. Try wiggling all the connections to make sure they make proper contact. I've had breadboards that sometimes didn't make a proper connection with the wires that I inserted.
    – Gerben
    Jan 29, 2021 at 14:13
  • So I've tried wiring the MAX7219 chip up myself following this as a guide: wayoda.github.io/LedControl/pages/hardware I only wired up the first column because my breadboard is only so big (plus, I just need to see what's up) I seemed to have the exact same problem with the example code from circuito.io, but - when I loaded up the LCDemoMatrix example, which uses the wayoda.github.io/LedControl library instead, it works! I'm not sure what was wrong with the first demo I used, possibly the modification I used to just turn on a single led was wrong. Jan 29, 2021 at 18:26


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