using four 4 x 7 segment LED displays

Hi all,

I am wondering about how to run multiple 4 x 7 segment displays of this type, whish has 12 pins.

Running one is fine, but of course one runs out of pins when trying to use more. With a 74HC595 it is possible to run two with Arduino, but since the 74HC595 can be daisy chained, I was wondering how to daisy chain four 74HC595s to drive four of these displays? I think I could also use an ESP32 with its many pins for this, but diay chaining hjas been successful in a couple of other projects involving single 7 seg leds.

Many thanks for any eventual ideas & assistance-

cheers,

-h.

4x7.PNG

4x7.PNG

Use max7219 or ht16k33. Much simpler and superior to using 74hc595.

Use max7219 or ht16k33.

Upvote!

if your picture shows a 0.56" display I would use some of the premade modules with a HT16K33. If you really want to solder it - there are also some backpacks available for the HT16K33. The HT16K33 is I2C - so you will need 2 pins only.

Frankly, not only is the 74HC595 quite unsuitable for driving multiplexed displays because amongst other things you need transistors to drive the commons, but the whole idea of multiplexing in code is mind-numbingly tedious. :astonished:

A MAX7219 does everything correctly, eight digits per chip and any reasonable number of chips from the same three pins.. I am not familiar with the HT16K33 but much the same would apply. :sunglasses:

Here was I thinking the sub-standard displays based on the 74HC595 had disappeared from eBay/ Aliexpress but no, I found one (but it did take a bit of searching)! :astonished:

Aliexpress example

I cannot distinguish what the segment resistors are on that module - and have no intention of buying one to find out. I suspect they are 1k which would probably provide fairly even brightness for different digits.

There are some modules which use one 74HC595 per digit for static drive which would be just fine. :sunglasses:

Use max7219 or ht16k33

That's got my vote as well. About as cheap as the 595 IC and a lot less fussing about.

Is the original d-digit display common anode, or common cathode?
You can use a resistor and a supply to buzz it out and see what pins are doing what.
Pinout could be something like page 33 here
https://www.datasheetarchive.com/pdf/download.php?id=833543b3e4d1ddf284ee3804c0c590b2183674&type=P&term=410561K

Or perhaps the attached for a pinout

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