74191 to count up and down with no switch.

Discussion in 'The Projects Forum' started by gvesho, Nov 8, 2013.

  1. gvesho

    Thread Starter New Member

    Oct 19, 2013
    3
    0
    Hi guys. I'm new on the forums and new to electronics for about 2 years now. I'm having some trouble counting from 0-9 then 9-0 continuously on a 74191 counter. I understand that its a 4 bit counter and it counts to 16 so i created a glitch with a nand gate to count to 9 by teeing Qb and Qd to the nand gate. I can get the counter to count either up or down with a switch but im trying to get it count continuously with out a switch.

    So basically i wanted to count up from 0-9 then back down from 9-0 and over and over again. This is where i need some help understanding.

    Thank You

    Schematics
    CLK is coming from a 555 timer
    up down counter.png
     
  2. crutschow

    Expert

    Mar 14, 2008
    12,981
    3,221
    You can use the carry (pin 12) and borrow (pin 13) outputs of the 74191 to set and reset a latch that controls the U/D input.
     
  3. tshuck

    Well-Known Member

    Oct 18, 2012
    3,531
    675
    Look at the up/down pin on the counter... now, you want to toggle that when you hit a certain value, 0 and 9. Look at a T-flip flop...
     
    gvesho likes this.
  4. tshuck

    Well-Known Member

    Oct 18, 2012
    3,531
    675
    The '191 is a binary counter, the max/min and RCO won't be useful for a 0-9 count.
     
  5. gvesho

    Thread Starter New Member

    Oct 19, 2013
    3
    0
    i cant seem to find a t flip flop nor have i learned about them. is there any other way, maybe using gates???
     
  6. tshuck

    Well-Known Member

    Oct 18, 2012
    3,531
    675
    You can make any flip flop from any other with the correct addition of some gates.

    However, it need not be a T flip flop, it just needs to remember what direction the counter should be counting in, and change states when the last count of a sequence is detected...
     
  7. crutschow

    Expert

    Mar 14, 2008
    12,981
    3,221
    Partially true. I forgot that it's a binary counter, so he can't use the Carry out at the upper count but he can use the Borrow out for the 0 count.

    For a negative triggered (change state for a zero input pulse) latch, you can use two cross-coupled dual-input NAND gates.
     
Loading...