What can be used here?

Discussion in 'The Projects Forum' started by nikhilbansal87, Mar 3, 2009.

  1. nikhilbansal87

    Thread Starter New Member

    Mar 3, 2009
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    I require the application of an electronic stopwatch. The function to be performed is as follows: A proximity switch senses a part and sends a signal to a relay. The relay activates a stop watch. Then after some .5 seconds, one more proximity switch senses the same part( it is under rotational motion). Again a signal is sent to relay and then to stopwatch to stop the count. The stopwatch should now display the stroke time of the part, that is, the time elapsed between the two proximity switch signals. When the next cycle starts, one more signal is sent to the stopwatch to reset itself. Suggest what can be used here. I am not able to come up with any device that exactly meets my requirements. Please suggest sth.
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,646
    2,345
    Hello,

    What kind of material is the part you try to detect with the proximity detector ?
    Is the time measurement very critical ?
    I think it is better to use an optocoupler than a relays.

    Greetings,
    Bertus
     
  3. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    How many buttons, on the stopwatch, perform your function if you use it manually?
    Is Start/Stop one button or two?
    Is Reset a separate button?

    I've interfaced stopwatches with 4066B analog switches. If Start/Stop is one button, you can diode-OR the proximity sensor outputs. The Reset depends on your stopwatch.

    Ken
     
  4. nikhilbansal87

    Thread Starter New Member

    Mar 3, 2009
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    The part to be sensed is a plastic part and therefore, i am using IR proximity switches.
     
  5. nikhilbansal87

    Thread Starter New Member

    Mar 3, 2009
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    The stopwatch has 2 buttons. One is the start/stop button. The other button is the reset button. This button also serves the purpose of having split lap times.
     
  6. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Is this how it functions manually?
    Start/Stop Button: Count starts
    Start/Stop Button: Count stops
    Reset Button: Counter zeros
    Start/Stop Button: Count starts.....

    How long is it between the stop of one cycle and the start of the next? Is it variable? What is the output of the proximity sensors...a link perhaps. Are the relays just to interface with the stopwatches, or is there another purpose for them.

    ken
     
  7. nikhilbansal87

    Thread Starter New Member

    Mar 3, 2009
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    The relay just serve as the interface to operate a stop watch. They serve the purpose of getting multiple outputs at one or two locations. The proximity sensors give an output signal ( i dont know its type) but it can be fed into the relay or directly to the stopwatch thing. And the stopwatch works in exactly the same manner as u pointed out. Their is no time gap between the end of one cycle and start of another. It happens immediately. It is not variable.
     
  8. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    If it's only 0.5 seconds between Start and Stop, and the Reset must occur immediately before the Start and there is no time between Stop and Start... how are you going to read the time on the stopwatch? It will always appear to be counting up.

    Relays take a finite time to open and close...up to 100mS. This will affect you timing accuracy. Relays contacts are subject to contact-bounce and can give you multiple openings-and-closings as they are switched on. There are "debounce" circuits to get around this, but they will add in timing delays.

    There may be other ways to accomplish what you set out to do. Rather than try to fix a solution, can you describe what the real world problem is, that we are trying to solve?

    Ken
     
  9. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    Let me see if I understand what is wanted...

    You wish to view the time it took for the immediately preceding half-revolution of a part in constant rotation at approx 60rpm?
     
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