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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.

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  • 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

1 Answer 1

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It's likely that it is just the orientation of the module is wrong. Pull out the LED module, rotate 180 degrees, put it back in and it should work. The dot point should be on the bottom right.

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