Digital Counter

Discussion in 'The Projects Forum' started by emilj726, May 29, 2013.

  1. emilj726

    Thread Starter Active Member

    Oct 1, 2010
    52
    2
    I have designed a 8-bit digital counter circuit using the 74HC163. The clk is coming from a 200Khz 74hct14 based oscillator circuit.
    The idea of the design is the counter has to count to a certain number within a give time (time base). Lets say it needs to count to 200 in 1ms. For the purpose of my design is that when the 1ms time is up I stop counting and see that the counter has gotten to that count, if not than there was a frequency change in the circuit.
    what I do in my circuit to acomplish this is:
    I have cascaded 2 4-bit 74hc163 counters to get a 8 bit counter. When the first counter reaches its max count of 15 RCO goes high, I use this as a input to B of a Monostable chip using a 74hc123 to trigger a 1ms one shot. What I am having issues with is the one shot output is always high. Is it Re-triggering? Is the counter resetting and starting count over again and again?
    Can anyone help?
    thanks!
     
  2. tshuck

    Well-Known Member

    Oct 18, 2012
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    675
    For all those words, a picture is better, please give a schematic.
     
  3. emilj726

    Thread Starter Active Member

    Oct 1, 2010
    52
    2
    Its on a cad software I don't think you can see it.
    Its just two 74HC163 chips cascated together the oscillator is going into the CLK input. The one shot is triggered out of the first counter chips RCO output.
     
  4. tshuck

    Well-Known Member

    Oct 18, 2012
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    You could always do a screenshot if you don't know how to export it to an image file...
     
  5. emilj726

    Thread Starter Active Member

    Oct 1, 2010
    52
    2
    Here is a shot of it!
     
    Last edited: Jun 2, 2013
  6. davebee

    Well-Known Member

    Oct 22, 2008
    539
    46
    Your clock is running at 200 kHz, then is divided by 16, resulting in a U31 RCO output rate of 200/16 = 12.5 kHz, 12.5 times faster than your one-shot.

    Won't that continuously retrigger the one-shot before it completes its 1 millisecond pulse?
     
  7. emilj726

    Thread Starter Active Member

    Oct 1, 2010
    52
    2
    Thats kind of what I am asking. I have moderate circuit board design experience but this is the first time designing something that has to do with digital chips(74hc163).

    I am trying to figure out a way I can trigger that one shot circuit only once.
     
  8. crutschow

    Expert

    Mar 14, 2008
    12,977
    3,220
    You can connect the output of the counter to inhibit its input at the end of the count so it stops counting. Then you reset the counter to restart the count.
     
  9. davebee

    Well-Known Member

    Oct 22, 2008
    539
    46
    Is this what you're trying to do - "Given a clock signal of around 200 kHz when healthy, make a circuit that will generate an alarm signal if that clock drops below 200 kHz."

    Could this be accomplished with just the oneshot?

    What if you reconfigured your oneshot to run at about 180 kHz rate.

    Feed the 200 kHz signal to its trigger.

    That way, the one-shot output would always be set unless it failed to receive its expected periodic trigger command, so an unset state from the one-shot would correspond to too low of a frequency on its input.

    A potentiometer for the one-shot timing resistor would let you adjust the one-shot's sensitivity to the clock being monitored.

    You would probably need to add more logic to this, to ignore the output of the one-shot until the clock is initially healthy, and to latch any momentary unset state, if that's what your circuit needs.

    Would that accomplish what you're trying to do?
     
  10. emilj726

    Thread Starter Active Member

    Oct 1, 2010
    52
    2
    Thats exactly what i have been trying to achive. When the oscillating frequency hence clock goes below a certain frequency to switch an led on.
     
  11. emilj726

    Thread Starter Active Member

    Oct 1, 2010
    52
    2
    when the 74hc163 gets to a certain count I want the counter to stop counting and keep that number. The way I do it is by having 3 binary iputs that equal the value 200 into a 3 input nand gate. The idea here is, as soon as the counter hits this number I want the low out out of the nand to stop the counter. I basically do this by routing this low back to the LOAD(bar) input and the counter does stop counting. Just wondering if this is a correct way of doing this?
     
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