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7 segment displays — Parallax Forums

7 segment displays

DAVID COOKEDAVID COOKE Posts: 42
edited 2010-09-08 15:52 in BASIC Stamp
I have the basic stamp homework board
I want to drive 3 separate 7 segment displays
is this possible?
I would appear to need 24 output pins so there is insufficent on a single BS2

thanks
david cooke

Comments

  • LeonLeon Posts: 7,620
    edited 2010-08-31 03:37
    If you multiplex the displays you will only need 10 outputs.
  • MorrolanMorrolan Posts: 98
    edited 2010-08-31 03:54
    Another option (although involving much wiring) would be to use a 7 segment display driver such as a CMOS 4026 IC. http://www.kpsec.freeuk.com/components/cmos.htm#4026

    However you would require one of these for each digit...
  • DAVID COOKEDAVID COOKE Posts: 42
    edited 2010-08-31 04:28
    thanks
    presumably i would also need a 555 for each 4026

    the aim is to produce a small display to show windspeeds in the range 0.0 to 9.9
    (and a further module which is blank for positive wind, and shows a "-" for negative


    dc
  • electrosyselectrosys Posts: 212
    edited 2010-08-31 04:36
    Have a look at -StampWork- EXPERIMENT #10: A DIGITAL CLOCK, page:67

    StampWork:
    http://www.parallax.com/Portals/0/Downloads/docs/books/sw/Web-SW-v2.1.pdf
  • MorrolanMorrolan Posts: 98
    edited 2010-08-31 04:37
    No you don't need a 555 for each 4026 - you can use PULSOUT in a FOR-NEXT loop to increment each digit the specified number of times.

    If you pulsed between 1 - 10 pulses (10 is for the 0) you would get that as the result on the display. However you can chain multiple 4026's together so that every time the 1st digit hits 10, it increments the 2nd digit, so you can then display between 0 - 99 from one pin.

    This is useful if you're doing say a temperature display and don't need individual control of each digit.

    I also connected all of the reset pins together to 1 pin on the BASIC Stamp so that I can reset all 3 digits at once (my project measured temperature to .1 of a degree) and I simply toggled this each time I wished to refresh the displays.

    I can provide example code if required when I am at home.
  • TCTC Posts: 1,019
    edited 2010-09-01 15:22
    what about maxim's MAX7219 there is info on parallax on how to use it.
  • Martin_HMartin_H Posts: 4,051
    edited 2010-09-01 16:03
    Would this be an ideal application for a serial to parallel shift register? A 74HC595 can turn 3 pins into eight and latch the output. You can also serially daisy chain them so they have 16 outputs.
  • Invent-O-DocInvent-O-Doc Posts: 768
    edited 2010-09-01 16:06
    Also, if you check out the parallax web-page on the SX chip (end of life), there is a basic interpreter called SX/B. The SX/B documentation has a sample of how to drive 7-seg displays in the exact manner you need to do. I suggest you peruse it - there is also a sample SX/B program with code you can use as an example. Granted, SX/B is a lot faster than a stamp, but this should be a good starting point. (You really want to multiplex).

    Your other options are to use a 7-seg driver, buy a serial IO 7-seg display, or use serial shift registers.


    Good Luck
  • DAVID COOKEDAVID COOKE Posts: 42
    edited 2010-09-02 10:17
    colleagues
    many thanks for your comments and advice

    dc
  • RavenkallenRavenkallen Posts: 1,057
    edited 2010-09-04 08:41
    You could multiplex the displays by having all the segments on the same data lines and then just toggle the common anode or common cathode really fast...
  • bwittbwitt Posts: 7
    edited 2010-09-08 15:52
    go to the what is a microcontroller text in the dowloads section and there is info there
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