How do i make a ls74192 counter start at number 69. URGENT

Discussion in 'Homework Help' started by DanRab, May 4, 2015.

  1. DanRab

    Thread Starter New Member

    May 4, 2015
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    Hey there.
    I am designing an up/down counter system for a university project and need to start the counter at a certain number-69 and it must not go higher than said value. The counter must also be able to count down to zero and stop when it gets there.
    The counter must start at 69, be able to ccount down to zero and no further and be able to count up to 69 when started.'
    It is a 74192 counter to a 7447 decoder.
    Thanks!
     
  2. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
    2,504
    380
    hi,
    Use the PL pin on the 192 to preload the counter/s with 69, also either detect 00 or use the down carry output.

    Post a diagram showing how this would be done and we can check it out.
    E
     
  3. DanRab

    Thread Starter New Member

    May 4, 2015
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    This is what i have so far multisim pic.png
     
  4. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    2,815
    834
    You have two conflicting statements. "It needs to count up to 69 when started" and "it needs to start at 69." Which is correct.?

    Think of how the preset and reset (or load and clr) inputs can be used. Hint: your problem description contains these answers.
     
  5. DanRab

    Thread Starter New Member

    May 4, 2015
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    So, when it starts up it must display 69 then once it has been counted down to any arbitrary value it must be able to count up once again to no higher than 69. Hope that clears things up
     
  6. Reloadron

    Active Member

    Jan 15, 2015
    969
    235
    So on your 74192 you will use your presets which in your drawing are all currently tied to ground. However, first things first, starting with U6 in your drawing. You have S1 & S2 going to the Dn and Up count inputs. With a 74192 holding for example pin 5 High and applying a clock pulse to pin 4 will result in a down count, holding pin pin 4 High and applying a clock to pin 5 will result in an Up count. If you plan to use a toggle switch to clock the up or down count you will need some switch debounce in there. How do you plan to clock the 74192?

    As to the presets. Each 72192 has 4 presets, they are pins 9, 10, 1, and 15 which are D, C, B, and A. So for example since in your drawing U6 is the LSD (Least Significant Digit)you want to set a "9" 0n U6. A good choice for those pins is a 4 switch dip switch. OK so for a 9 you would ground pin 9 (D) and ground pin 15 (A) which gives you 8 + 1 = 9. Next U5 is the "6" and a 6 would be a 4 + 2 or in this case a C and B so you ground pins 1 and 10. Make sense? You also need to use the Load function so tie pin 11 on both chips together with a push button switch to ground. Momentarily pressing the push button will momentarily ground pin 11 resulting in loading the preset values we just setup.

    Again, how do you plan to clock the chips? Well actually your LSD chip which is U6?

    Ron
     
  7. DanRab

    Thread Starter New Member

    May 4, 2015
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    The chips are going to be clocked with a 55 timer in monostable
     
  8. Reloadron

    Active Member

    Jan 15, 2015
    969
    235
    Then set it up as I mentioned and route the clock pulses as required for Up or Dn counting. Finally if this is Homework or Schoolwork it should not be in this General Chat section but in the Homework section.

    Ron
     
  9. MrChips

    Moderator

    Oct 2, 2009
    12,452
    3,371
    Since this is a school project, thread moved from General Electronics Chat to Homework Help.
     
  10. MrAl

    Well-Known Member

    Jun 17, 2014
    2,440
    492
    Hi,

    To detect a given count you can use a four input gate and inverters, or four two input exclusive OR gates for four bits. For eight bits you just double the circuit.

    With a four input NAND gate for example and detecting a '6' using four bits, you would connect an inverter to bit 0 and bit 3, and run bits 1 and 2 directly to the NAND gate inputs. When the right code (6) comes up, the output of the NAND gate goes low and that's the only time it will go low.
    To detect a '9' you do the same, except reverse the role of the inverted signals and non inverted signals, so that NAND output goes low when a '9' appears at the inputs.

    To use four two input XOR gates, you run all the signals right into one input of each gate, and then either ground or pull up the other inputs depending on what code you want to detect, then AND all the outputs together.

    There are a lot of other ways to do this too. For example, they make a general purpose binary comparator IC that compares two four bit inputs. You run your signals into one set of inputs, then set the other four inputs to whatever code you need to detect, and the equals (=) output goes high (or low) when the right code appears on the input.

    You can also use a 1 of 16 decoder for four bits, and a 1 of 8 decoder for three bits, but the 1 of 16 decoder is a big chip.

    When you get the right code you stop the count, possibly with some gate.
     
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