A Low RPM Alarm Using 74HC or 4000 Series Logic. No MCU allowed.

  • Status: Closed
  • Prize: $100
  • Entries Received: 13
  • Winner: osamaelkomy

Contest Brief

I need a simple circuit using common hardware parts that measures the high width of a TTL pulse and if it exceeds 3 seconds a logic output is set high as an alarm.

If the pulse becomes shorter than 3 seconds the logic output is set low so alarm is turned off.

A 32768Hz clock is available. Maybe a 74HC series binary counter might work. Or specify your own clock generator.

We want simple 74HC logic, or 4000 logic. Not MCU and not FPGA.

When we choose the circuit we will build it to confirm it works before awarding prize.

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Employer Feedback

“Excellent Freelancer and good communication”

Profile image tonyoatlands, Australia.

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Public Clarification Board

  • tonyoatlands
    Contest Holder
    • 2 months ago

    Thank you every body for your ideas. But NO ONE has provided a schematic design we can build.

    We have been given ideas only. Please provide a schematic with component values.

    • 2 months ago
  • tonyoatlands
    Contest Holder
    • 2 months ago

    We already know the job can be done. We don't need ideas and suggestions. We need a working design that we can build and test. Today we have four entries. No entry shows a working complete design!

    • 2 months ago
    1. Muzafarbaloch
      Muzafarbaloch
      • 2 months ago

      Sir! here you are kindly check #8 . it contains the complete working circuit design. Thanks

      • 2 months ago
  • Muzafarbaloch
    Muzafarbaloch
    • 2 months ago

    Certainly, you can use a 74HC4040 binary counter and other basic components to create a circuit that measures the width of a TTL pulse. Sir Kindly check my entry #8 . everything is mentioned there.

    • 2 months ago
  • osamaelkomy
    osamaelkomy
    • 2 months ago

    I'm confused about your requirements for this contest.!
    I gave you the design schematic and a simulation. The simulation confirmed that the design works perfectly with 74HCXX logic chips. What else do you need ?

    • 2 months ago
    1. osamaelkomy
      osamaelkomy
      • 2 months ago

      There are other options to replace 74HC123 that can generate the 3s pulse like 74HC4538. Does using MMV acceptable ? or you prefer counter solution ?

      • 2 months ago
    2. osamaelkomy
      osamaelkomy
      • 2 months ago

      Other thing about circuit behavior, when the alarm signal is activated ( if the PW > 3s), what should happen when the PW returns to normal condition (PW < 3s)? automatically deactivate the alarm, or provide manual deactivation (Reset)?

      • 2 months ago

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