7 segment

Discussion in 'The Projects Forum' started by aman92, Apr 1, 2013.

  1. aman92

    Thread Starter Member

    Aug 22, 2012
    I need to interface three 7 segment displays with 8085. Now I need to control each of them individually through a push button. The 7 segment display will run a counter and I will use the push button to turn on and then turn off the counter and then display the no at which i stopped. I need to do this with three different 7 segments and display all 3 numbers simultaneously.

    Now I need to knwo whether I should create a separate output port for each display or whether it can be achieved by multiplexing them
  2. tshuck

    Well-Known Member

    Oct 18, 2012
    Multiplex them.
  3. absf

    AAC Fanatic!

    Dec 29, 2010
    What I/O ports did you have on your 8085 mpu? Do you have 8255 connected to the 8085 or you have connected latches like 74LS573 as output ports?

    You can choose to multiplex the 3x 7 segment LED (10 IO lines) or directly connect them to the IO lines (21 IO lines) though 21 NPN or PNP transistors or 3x ULN2803 chips.

  4. takao21203

    AAC Fanatic!

    Apr 28, 2012
    a 74HC244 buffer is good enough actually for small 7-segment displays.

    Normally LED displays are multiplexed, and I'd recommend a 3-digit Module which already is multiplexed. They are not expensive.

    Even for the sinks, I have sometimes used 2x LCX244 bit lines in parallel. It is OK since they are also updated in parallel.

    No brightness variation, having such a sink.

    Discrete transistors + resistors is quite a hassle.
  5. absf

    AAC Fanatic!

    Dec 29, 2010
    Yes, 74HC244 can be used as input ports for 8085 too.