MAX7219 8 Digit Seven Segment Display Module (HCMODU0082)

LCD, TFT, OLED, LED modules
andrew
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Re: MAX7219 8 Digit Seven Segment Display Module (HCMODU0082)

Post by andrew » Tue Apr 12, 2022 12:20 pm

I note that once loaded, if I press the boards reset button, the second display flashes all segments momentarily, but blanks and leaves nothing on the display.
Hmm, that sounds like one of three things, either the supply voltage is too low on the second module (possibly related to my comments in the previous post), a noisy power supply or data line causing data corruption, or a bad cable or connection somewhere.

When you swapped the modules around did you keep the cables in the same order? If so, are you able to try a different cable between the first and second modules just in case is a bad cable between the two?

Also, do you have a volt meter that you could check the VCC output pin on the second module with? Failing that here's a couple of things you can try to see if it's the supply voltage being too low to the second module:

Connect a separate 5V supply from your Arduino to the VCC pin on the second module rather than linking it through the first module. You can keep the GND connection daisy-chained through the first module if that's more convenient. If you’re using an Uno you can get a separate 5V from the IOREF header (edit: 5V Arduino only) or from the ICSP header.

The other thing you may be able to try is to short the diode on the back of the first module (should be marked D1) with a wire, paper clip, or tweezers then write to the modules again.
Last edited by andrew on Tue Apr 12, 2022 12:23 pm, edited 1 time in total.
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DennisJ
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Joined: Mon Apr 11, 2022 9:19 am

Re: MAX7219 8 Digit Seven Segment Display Module (HCMODU0082)

Post by DennisJ » Tue Apr 12, 2022 12:22 pm

** SOLVED ** Think our posts crossed

Fed the VCC for the second display direct from the 5v rail of the UNO board, not piggy backed from the first display.

So, as you thought earlier, it has something to do with the diode on the board.

I'll go and do some measuring :)
(Edit - rail 5.4v. supply to first board - after board 1 diode = 4.7v, and then after board 2 diode = 4.1v).

Guess either feed them seperately or as you say, short out the diode (assuming wiring checked).

Thanks for your valuable assistance.

andrew
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Joined: Sun Aug 05, 2012 4:15 pm

Re: MAX7219 8 Digit Seven Segment Display Module (HCMODU0082)

Post by andrew » Tue Apr 12, 2022 4:39 pm

That's great. I can see the reason for the diode but it does cause problems with daisy-chaining them. Normally two a fine though.

Thanks for confirming anyway. I'll put a note in the description about the diode when connecting multiple modules.
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