Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Seven segment display acting wierd.

  1. Apr 28, 2012 #1
    Ok for class, I had this 7segment display(common cathode) and it worked great. Then I bought more, but I bought the common anode kind. And this time, it doesn't work so well. For some reason the numbers change when i wave my hand over the power supply; im not even touching it. I'm using cd4543 decoder with the ld5161.

    ..wait i just tried again, and nothing happens but when i pick up the power supply all the segments turn on even though the switch is on 0000 wtf...

    can someone tell me why my seven segment display does wierd things when i mess with the batteries?
  2. jcsd
  3. Apr 28, 2012 #2


    User Avatar
    Science Advisor
    Gold Member

    Common cathode and common anode will need different circuit methods to drive them
    I would hope you are not trying to mix them or use the same circuit to drive one or the other ??

  4. Apr 28, 2012 #3


    User Avatar
    Science Advisor

    The 4543 has to be used with a common cathode display.

    To turn a segment on, you make that output high.

    If you connected a common anode display in circuit, the LEDs would only turn on if the anode was connected to the positive supply, but then a high drive signal would turn the LED segment off and a low signal would turn it on.

    So, you would have to invert every drive signal.

    Try to get a common cathode display.
  5. Apr 29, 2012 #4
    nope. 4543 is common anode. just tested inverting everything, the light doesn't turn on at all. it stopped blinking though. i think before the resistors were touching so it was acting weird. it still doesnt work though. it stays lighted on the middle segment only now, all others don't turn on and nothing changes when i flip the switches.

    is anyone familiar with the ld5161bg? i bought this on ebay.

    edit: nvm ur right. the truth table looks like it is common cathode.
    Last edited: Apr 29, 2012
  6. Apr 29, 2012 #5


    User Avatar
    Science Advisor

    According to the data sheet, it drives common cathode displays. This is shown by the outputs being high for lighted segments.

    You connect them like this:
    http://park8817.com.ne.kr/COMMON_CATHODE_CIRCUIT.jpg [Broken]

    To make it work with a common anode display, you would have to connect it like this:

    Last edited by a moderator: May 5, 2017
  7. Apr 29, 2012 #6


    User Avatar
    Science Advisor
    Gold Member

    never heard of it and nothing on google... what is it an IC ? a display?
    have you got the ebay link ?

Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Seven segment display acting wierd.
  1. 7 Segment Display Help (Replies: 5)

  2. 7 Segment LED display (Replies: 7)