lolapi
Posts: 5
Joined: Mon Oct 26, 2020 5:18 pm

Multiplexing 7 segment display with MAX7219

Mon Nov 23, 2020 11:49 am

Hello yall (i got a MAX7219 module, Raspberry Pi, TRU-7S2-80RAG 0318 7segment display)
I'm pretty bad at electronics and I don't know how to read this manual about the MAX7219. There are just too many diagrams which make me frustrated. Here's the manual https://datasheets.maximintegrated.com/ ... AX7221.pdf
I also don't know where to connect the 7 segment display pins https://asset.conrad.com/media10/add/16 ... -80rag.pdf (the model is TRU-7S2-80RAG 0318)

I would be pleased of any kind of help :)
I hope you are having a wonderful day
Lola

markkuk
Posts: 248
Joined: Thu Mar 22, 2018 1:02 pm
Location: Finland

Re: Multiplexing 7 segment display with MAX7219

Mon Nov 23, 2020 12:19 pm

MAX 7219 is for common cathode displays and TRU-7S2-80RAG is a common anode display, so they aren't compatible with each other.

lolapi
Posts: 5
Joined: Mon Oct 26, 2020 5:18 pm

Re: Multiplexing 7 segment display with MAX7219

Mon Nov 23, 2020 1:09 pm

Ufff well that was unexpected...
Which controller should I buy so that it is compatible with my 7 segment displays (TRU-7S2-80RAG 0318)
Kind regards
Lola

hippy
Posts: 8960
Joined: Fri Sep 09, 2011 10:34 pm
Location: UK

Re: Multiplexing 7 segment display with MAX7219

Mon Nov 23, 2020 2:33 pm

markkuk wrote:
Mon Nov 23, 2020 12:19 pm
MAX 7219 is for common cathode displays and TRU-7S2-80RAG is a common anode display, so they aren't compatible with each other.
It would be recommended to use common cathode displays.

Common anode displays can be used with a MAX7219 providing they are wired correctly but one loses the 'per digit' functionality, and the segment to register bit mapping will be different to how it is described in the datasheet. That can however be resolved in software.

emma1997
Posts: 1319
Joined: Sun Nov 08, 2015 7:00 pm
Location: New England (not that old one)

Re: Multiplexing 7 segment display with MAX7219

Mon Nov 23, 2020 6:05 pm

Here's the guy who managed that: https://marco-difeo.de/2013/02/21/drive ... -displays/

Still an easier path for me was to spend a few pennies on cheap inverters (hc00, hc04, hc240, etc). I tried the 7219 software route and also driving directly off GPIO. Definitely not worth it if time is worth more than $.01/hr. Unless maybe an educational experience or therapy (like basket weaving).

There are two other chips that do CA but expensive and almost impossible to buy in small quantity. I learned my lesson and stick with CC exclusively now.

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