Maximum number of 7 segment displays using multiplexing

Projects General Guidance
1

Hello everyone,

I have used 24 seven segment displays using multiplexing (74HCT595 & ULN drivers) successfully. Now I have to build a board having 48 & 75 displays in two parts. My question is whether a single arduino is capable of driving this number of displays (without flickering)? All the displays are 0.56" size.

I can use MAX7219, but they are quite costly, and one chip supports only 8 displays. Whereas I can get arduino nano or pro mini at the price of single MAX7219. If I can know maximum number of displays a single MCU can handle, I can break the displays in parts.

Thanks!

2

If all digits are completely refreshed every 4mS or so, then there should be no noticeable flicker to the human eye.
But how did you organise the 24 displays ? As one long chain of 595s or did you split it ?
There are also different multiplexing strategies such as one digit with all needed segments lit each cycle, or 1 segment with all digits using that segment lit each cycle.
Maybe a quick diagram of what you have already got working would be good.

Incidentally, some Ebay retailers have Max7219 / Max7221 chips around $1 each and this would mean less soldering (only 1 current limiting resistor per chip)

3

That sounds highly dubious for one, and - so what?

4

You can get cheap (possibly counterfeit) MAX7219-like chips from the same sources that sell cheap nanos and pro-minis. Like https://www.aliexpress.com/item/32875328547.html - I have no idea how trustworthy or operational those are.

The TM1637 is also popular.

6

Thanks for your reply.

I had cascaded 6 number of 595s & they were used to drive 6x4 matrix of the displays. The microcontroller used was 89S52 with 11.0592Mhz crystal. It was running very smoothly.
Anyway, I have decided not to use multiplexing as the available PCB space is limited and required peak current will be very large, it is described in this link. https://www.avrfreaks.net/forum/how-many-7-segment-digits-can-you-multiplex

7

Thanks everyone for your replies.
@Paul_B I am getting original MAX7219 and arduino nano or pro mini at ₹200 here in India. But, chinese version of MAX7219 is available at ₹95.
@westfw I had used earlier cheap MAX7219-like chips without any problems, so I will continue with them. TM1637 is also a good option ₹35, but it can only drive 6 displays & cannot be cascaded (I think), so it will need more number of MCU pins. Thanks!

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