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Multiplexing Project — Parallax Forums

Multiplexing Project

MRMR Posts: 46
edited 2009-01-05 19:39 in BASIC Stamp
I have a basic stamp 2p40 (the 40 pin version)

I have 10 7 segment displays all (common anode).

I would like to learn how to multiplex the digits to display 0-9.

I need help understanding the following.

1. How do I turn on and turn off each display? Should I use an external Chip or clock? If so How do I do it?


2. How do I ensure the displays will be bright enough?
A. I know about using transistors.
B. What size resistor should I use for these displays to ensure proper brightness?

Comments

  • MSDTechMSDTech Posts: 342
    edited 2009-01-04 15:10
    You might want to download the Stampworks manual from the Parallax website at:
    http://www.parallax.com/Portals/0/Downloads/docs/books/sw/Web-SW-v2.1.pdf
    Look at Experiment Number 31 which goes into the use of the Motorola MC14489 for multiplexing the seven segment displays. Although this only does 5 digits, with two of the units you would should be able to control all 10.
  • $WMc%$WMc% Posts: 1,884
    edited 2009-01-04 22:14
    MR

    I think the MC14489 is the why to go as MSDTech suggested. Go take a look at the Data sheet for the MC14489 "mouser.com",Plug the part# in the search window then click on Data sheet when the page opens. Since this is a 5 digit decoder and Your loading it w/ 10 digits in ,5 digits will over flow. the "data out" pin on the first MC14489 should be tied to the "data in" pin on the 2nd MC14489. This will make use of all 10 digits sent out. I forgot to look at the BANK out pins , But this will be in the datasheet

    Hope this helps, If not drop another post reply and will go from their.

    _____________________$WMc%_____________

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  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2009-01-05 19:39
    Hello, the MC14489 is designed for Common Cathode displays, as is the MAX7219. If the desire is to learn to multiplex you wouldn't want to use a driver chip anyway. You would drive the segments via resistors and drive the anodes with a counter chip and some transistors. This is one way to go and specifics really depend on the source voltage of the displays, but it does give you some ground work.

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    Chris Savage
    Parallax Engineering
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