7 Segment Display Question

Discussion in 'General Electronics Chat' started by thekiwimaddog, Jan 29, 2013.

  1. thekiwimaddog

    Thread Starter New Member

    Jan 29, 2013
    Hi, I've been reading about 7 Segment displays and everyone is saying you need to switch between the segments at great speed to make them work correctly.
    Is this true?
    I can understand that it might be more efficient that way, but what is to stop me from just lighting them at the same time? From what I've read these are all independent LED's that share a common cathode.

    So am I right in saying that if I independently resist each LED rather than a generic one at the cathode this should be fine?

    Are there and heat issue by lighting them all together?

    Do these 7 Segment Display drivers do all the fast switching for you?

    Thanks for any info you can give me.

  2. MrChips


    Oct 2, 2009
    Ok, you are referring to two completely different circuit designs.

    There is nothing to stop you from interfacing two or more 7-segment displays to their individual data bits.

    What you are referring to is a technique called time-multiplexing which reduces the number of data lines to drive multiple 7-segment displays.
  3. thekiwimaddog

    Thread Starter New Member

    Jan 29, 2013
    OK, thanks for the clarification!
    I'll have a read up about that.

  4. bance


    Aug 11, 2012
    If you are using a Micro to control the 7 segment display, and you are using more than 1 digit, then you will exceed the maximum ratings for the micro-controller. Multiplexing is a technique that overcomes this limitation, by using persistence of vision. The human eye cannot tell that the leds are flashing because it happens so quickly. :D
  5. ScottWang


    Aug 23, 2012
    If you want to know more about the scan for LED display, then you can refer to the below on page 6 - the internal structure of MC14553, and the LED display circuit using MC14553 and MC14543 on page 7.

    CD4553 datasheet.

    When you using Mcu to scan the LED display, the method is the same with the circuit.