Perplexed by Charlieplexing

[PerranOak]

So, I've looked into Charlieplexing (CP) as suggested by a contributor and I love it!

I have made simple sets of discrete LEDs light according to the principles of CP but have now hit a snag.

I want to use CP for 7-seg displays but with the common anode (or cathode) the individual digits can't be "split-up" to be paired.

What do people do?

[Bassman59]

So, I've looked into Charlieplexing (CP) as suggested by a contributor and I love it!

I have made simple sets of discrete LEDs light according to the principles of CP but have now hit a snag.

I want to use CP for 7-seg displays but with the common anode (or cathode) the individual digits can't be "split-up" to be paired.

Don't do Charlieplexing. Just do regular multiplexing. Use 7 micro/FPGA output pins for the individual segment signals (cathode for common anode displays). Segments 0 on all digits are driven by a common pin. Then the anodes are driven by individual pins, one active at a time.

[PerranOak]

Ah yes but my goal is to operate a four digit, 7-seg display with a microcontroller in an 8-pin package.

Don't ask me why, it's just my thang! 

[matseng]

We charlieplex the entire display and not the individual digits.  It won't give you as good gains as with loose leds at any arbitrary number of displays . But you can drive 8 displays with just 9 pins from the mcu. See my old ancient instructable about the subject at https://www.instructables.com/id/Charlieplexing-7-segment-displays/

[PerranOak]

Brill, cheers I'll have a look.

[rstofer]

Ah yes but my goal is to operate a four digit, 7-seg display with a microcontroller in an 8-pin package.

Don't ask me why, it's just my thang! 

Since you can't use reverse polarity as in CP, you are pretty much stuck to at least 7 pins for the segments plus additional pins for digit selection.  I don't see parallel connections happening with an 8 pin controller.

But you can use a serial driven 7 segment display which just uses 2 pins and the SPI protocol.  It would take 3 pins if you decided to control SS'

https://www.sparkfun.com/products/11441