Digital Clock Using 74192

Discussion in 'Homework Help' started by Codeman, Nov 27, 2015.

  1. Codeman

    Thread Starter New Member

    Nov 27, 2015
    Hello All,

    I'm new to the forum and I'm having trouble with a university project. I am using a 555 timer, four 74192 up/down counter chips, four 7447 displays, and four 7 segment displays to function as a 24 hour clock. The part I'm stuck on is I've never used these chips to count up to a certain number and reset back to zero before. What I'm used to is starting at a preset number and counting down to zero.

    So this is how I imagined it would work:
    1. 555 pulses every minute and sends a signal to the first 74192
    2. The first 74192 chip is preset to 9 and the 1 minute pulse is sent into the Up clock pin
    3. While the 74192 chip is counting up it sends the data to 7447 and seven segment display
    4. When the 74192 chip hits reset after 9 it sends a carry pulse to the second 74192 chip
    5. The second 74192 chip starts at zero and counts up to 5 then resets to zero.

    Similarly the other 74192 chips will be preset and connected through carry. Max readout should be 24:00 and min should be 00:00

    So far, I have the first 74192 chip counting up to 9 and pulsing to the second 74192; However, the second 74192 is going 0 1 2 3 4 5 6 7 8 9 on the first cycle and then 5 6 7 8 9 0 on every cycle afterwards. Why is it not working like the first 74192?
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    Welcome to AAC!
    Can you post a schematic of your setup?
  3. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    Three questions...
    What signal exactly, triggers the second 74192 chip?
    What signal exactly, triggers the reset to zero of the second 74192 chip?
    Can you post a schematic of your circuit?
  4. Codeman

    Thread Starter New Member

    Nov 27, 2015
    I figured out what I needed to do. I just made it more difficult than it needed to be.

    To answer your questions though:
    1. No, I don't have any software to do that.
    2. The first 74192 signals the second to count up through the "carry" pin

    3. I set up an And gate that ran to the first 74192's 1-output and 4-output as inputs and then ran the output of the gate to the second 74192's "clear". To get this setup to work though, I had to put a pull down resistor on the clear so that the pin would toggle.
  5. MrCarlos

    Active Member

    Jan 2, 2010
    Hello Codeman

    What I understand from your original message is you're trying to make a 4-digit digital clock in 24-hour mode.
    Therefore only it has two digits for the hours and two for the minutes.

    Let me see if we agree:
    The counters for the minutes should count from 00, 01, 02, . .10, 11, 12, 13, . . . 57, 58, 59, 00.
    The counters for the hours should count from 00, 01, 02, . . . 10, 11, 12, 13, . . . 20, 21, 22, 23, 00.
    Right ?

    So you need to detect when the counter of the tens of minutes reaches 6 and in that instant reset both counters to 00.
    This can be accomplished with a 2-input AND gate connected to the connectors named MQ20 and MQ40. Because: 20 + 40 = 60.

    Using the same technique we can say that when the counters, for hours, reaching 24 You'll have to reset them to 00.
    This can be accomplished with a 2-input AND gate connected to the connectors named HQ4 and HQ20. Because: 4 + 20 = 24.

    Surely you know where to connect the outputs of these AND gates, right?

    No pull-down resistor is required. Gates bring the same effect inside.

    Carefully analyze the circuit shown in .PDF document I am enclosing you.

    I hope you have, in your design, the current limiting resistors for each segment of each display.
    And also you have a logical, appropriate level, applied to the inputs you are not using of the IC's.
    nephelem likes this.
  6. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    1) Use pencil and paper. Then tak a picture with a smartphone and upload your schematic.
    2) And where do you connect the carry output?
    3) If you reset on a 5, your counter will count 0, 1, 2, 3, 4. When it hits 5 it will immediately reset to 0. You need to AND the 4 pin and 2 pin.