Seven segment controller question - Is there a better way?

[Christopher4187]

Thanks for the reply. I don't understand why the shift register is more advantageous (or that much different) than using a port expander. Lets forget about cost for a second seeing as how the shift register is cheaper but we're talking about a one off device, not volume production.

The schematic you provided a link to shows pretty much the same thing I was thinking (which is perfectly fine by the way - I have no problems with it). He is using one shift register per digit, which is the same as the design I was thinking about. However, now that I think about it I can use a 23S17 and reduce my chip count from 5 to 3.

Does the shift register reduce the amount coding that you have to do? In other words, pretend you're a salesman, what's the selling point with using the shift register as opposed to a port expander?

[aerostar]

You said "the budget is paper thin." so usually 74HC etc stuff is cheaper than port expanders.

When I scanned your expander and the new one, I see that there seems to be a lot of settings to be sorted, so I looked for an easier route, hardware and programming.

The shift registers are easy to use, and the program is relatively straight forward.

You store the binary patten of each digit in on board pic eprom starting at location 0, so you have 10 values (led patterns) there 0-9.

you have your x=14 or whatever , THEORETICALLY 00014

If you store that 5 into an array eg numbers(0) = 4 numbers(1) =1 and so on

remember to send the least significant digit out first as that will be the far right hand on the display

you then do a loop something like

FOR COUNTER = 0 TO 4 ' 5 DIGITS
pattern = numbers(counter)
read patten , temp ' get the led patten into temp
then shift out temp to the shift register
next

you now have all the segments for the 5 digits done

with some extra programming you could make the leading "0"s be unlit.

[aerostar]

Presumably he has done his own thing - pity he did not have the courtesy tell us whether he went with shift registers or port expanders and why.

[Dave]

Chris4187, Personally I would use a MIC5842 for the shift register/driver as it has 8 bits and latch for each large led display.