2x 74HC595 via SPI interface, driving 8x 7-segment display

[andeug]

Hi,


I am looking to replicate the design below on 8x 7-segment displays, and for this purpose, I will need 2x 74HC595 via the SPI interface.

4-Digit-7-Segment-LED-Display-Module-Circuit.png (35.4 KiB) Viewed 585 times

Can someone please let me know, through an example, how I can multiplex those 8 digits on an Arduino Nano 328?
Is it possible to do it only via SPI, or will I need a common anode/cathode for each digit?


Thank you,
Andreas

[mnfisher]

The 74HC595 devices are daisy-chained - so writing values will 'push' the data to the second chip... So you just need to write sufficient data for both devices before latching the data. I haven't used this - but the MAX7219 works in a very similar manner.
Martin

[stefan.erni]

Hi Andreas

I need a common anode/cathode for each digit?

Yes, you need a common anode for each digit.
Note that each digit only lights up briefly, for example 1 msec, and then remains dark for 7 msec (with 8 digits).
you just can't see it with the eye so fast.

You have to do this with the esp32.

If you use a MAX7219 as Martin suggests, the Max will take care of this timing.
Ready-made modules with MAX7219 are available for just a few euros.

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2026-02-06_14-32-34.PNG (163.29 KiB) Viewed 458 times

[andeug]

The problem is that the MAX7219 does not exist officially in Flowcode's library, despite being quite a common product among hobbyists...

[mnfisher]

There are quite a lot of MAX7219 drivers around though - I've done ones for the 8 x 8 grids, digits and most recently - 32 x 32 (the last is the simplest and supports simulation too!)
The actual data required is simple - output to all of the attached drivers and then latch a line at a time.

Martin