2x MAX7219 needs 1x or 2x caps and resistors

Projects General Guidance
1

Hello

I am using an Arduino MEGA 2560 and interfacing to a MAX7219. For this MAX7219 I have 1x 100nF ceramic capacitor from 5V pin of MEGA 2560 continue along 5V rail. Then I have 1x 10k resistor from 5V rail to ISET pin. Then a wire to hook up to VCC of MAX7219. The MAX7219 is then connected to a 6 digit 7segment. Tested and this works well, all good. All digits show as per my code.

I then setup another MAX7219 like above, including additional caps and 10k resistor. It works and the 2nd display works correctly. So connection and code wise it's good.

However, for display 2 do I really need the 2nd load of caps and 10k resistor? What would happen if I didn't? I know that if I do not include then I will connect ISET Display1 to ISET Display2.

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Thanks for your help.

2

Yes.
Not only that but you need to connect the + and - power from those caps to the power input of the MAX7219.

If you didn't connect the resistors then you would not have any brightness control on any MAX7219 and this would be subject to interference pick up which would mean the brightness would not be constant and liable to change.

3

What if you posted an annotated schematic.

4

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