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7 Segment Display with DP — Parallax Forums

7 Segment Display with DP

morris4019morris4019 Posts: 145
edited 2009-05-14 16:57 in Robotics
This is gonna sound kind of dumb, but for some reason I cannot opperate the Decimal Point on my·7 segment display. There are only 8 pins, is there a combination I am suppose to use to use the decimal point?



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······ I'll try everything once [noparse]:)[/noparse]

Comments

  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2009-05-07 02:07
    With only eight pins, in either a common anode or common cathode configuration, the decimal point must not be connected. Do you have a schematic for the display?

    -Phil
  • morris4019morris4019 Posts: 145
    edited 2009-05-07 02:37
    no schematic, aparently this is an obsolete part and i'm having trouble finding a datasheet for it. I was kind of thinking maybe the dp is not connected. I have a few others (all scavanged from numerous different things) and they all work perfectly. Maybe just a bad one, i'm not going to worry about it too much. Thanks.

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  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2009-05-07 15:12
    Maybe I misunderstood…with 8 I/O lines you should be able to control a 7-segment display and the decimal point, since the common line doesn’t need an I/O pin. I would use a driver IC, or at least a shift register that can handle the current, but it can be done.

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    Chris Savage
    Parallax Engineering
  • W9GFOW9GFO Posts: 4,010
    edited 2009-05-08 15:36
    I think he means 8 pins on the display, one common, seven for the segments. From my brief research on 7 segment displays, the ones with decimals have 10 pins. You can save three IO pins by using a BCD driver such as the MC14511B.

    Rich H
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2009-05-08 18:59
    Regardless of the number of pins a display has, 7-segment displays with one decimal point use a total of 9 pins. Assuming common cathode with the cathode tied to ground, to light up the 7 segments plus the decimal point would require 8 I/O pins. You wouldn’t normally control the cathode via I/O pin unless you were driving more than one display and wanted to multiplex them. Take care.

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    Chris Savage
    Parallax Engineering
  • W9GFOW9GFO Posts: 4,010
    edited 2009-05-08 20:09
    Yes, understood. But if his 7 segment display has only 8 pins there is not much chance that he can light up the decimal point. Right?

    Didn't know about shift registers, looks like a better way to go than a BCD driver. Lots to learn...

    Rich H
  • kwinnkwinn Posts: 8,697
    edited 2009-05-09 02:08
    This could also be a display with a built in decoder/driver.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2009-05-14 16:57
    Why did I think he said 10 pins? To the OP...do you have a part number for this display so we can get a datasheet? Not all 7-segment displays support the decimal point. And then there are some that have left-hand and right-hand decimal points. In any event, without looking at a datasheet it would be impossible to say except to guess as other s have that it doesn't support the decimal point on this particular display.

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    Chris Savage
    Parallax Engineering
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