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I’ve got Led matrix 32x8 which is driven by MAX7219. Like this:

MAX7219 Dot Matrix Module Microcontroller 4 In One Display with 5P Line

When I power it up, I can see different glitches. How to power it up softly, without these glitches?

Michel Keijzers
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zhekaus
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1 Answers1

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What program are you using?

Possibly during startup (before initializing the signal pins), there are floating inputs.

Use either internal or hardware pulldown resistors to make sure 0 V is sent to all signal lines.

Michel Keijzers
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  • I am using arduino. Probably there is some noise on pins at first.How to suppress it? – zhekaus Nov 05 '19 at 10:31
  • By using pulldown resistors, they will force a pin/wire to go to GND level as long as there is no other signal on the line. E.g. try with one, find a pin of the MAX7219 that gives noise, add a e.g. 1 MOhm resistor from that pin to GND (and keep the jumper/wire to the Arduino as well). – Michel Keijzers Nov 05 '19 at 10:32
  • what pins should I pull-down? There are CS, CLK and DIN. – zhekaus Nov 05 '19 at 10:36
  • Ah ok, you are using SPI … probably if you pull the DIN (data in) pin low it should be improved. However, it should not be necessary for SPI normally. You initialize SPI early in your program? – Michel Keijzers Nov 05 '19 at 10:38
  • Actually, I don't use SPI. Pull-down resistor on DIN does no effect. I believe I need to find a way make be matrix be dark at initial powering up. Currently, when I plug it, it’s fully lightened. – zhekaus Nov 05 '19 at 11:03
  • Those pins seem to be SPI, so I'm a bit confused now how you control the MAX via your Arduino. – Michel Keijzers Nov 05 '19 at 11:08
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    Oh, yes, sorry, you're right. – zhekaus Nov 05 '19 at 11:15
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    pull-down 10K on CS pin solved my problem – zhekaus Nov 05 '19 at 12:34
  • @zhekaus ok :-) Thanks for the notification – Michel Keijzers Nov 05 '19 at 12:45
  • @zhekaus Did you only connected the CS pin directly to the GND pin with the 10K Ohm and also to the Arduino too? I am having similar problems so far (getting noise sometimes on the MAX display). – PiMathCLanguage May 02 '21 at 15:18
  • @PiMathCLanguage I did. – zhekaus May 03 '21 at 16:17