Which opto switch??

Discussion in 'General Electronics Chat' started by NornIron, Jan 22, 2014.

  1. NornIron

    Thread Starter New Member

    Nov 19, 2013
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    Hi everyone!
    I need some valued advice please!

    I am planning to use an optical switch to measure the speed of a motor which will be turning from speeds of between 20Hz to 100Hz, 1200-6000Rpm.
    I am unsure which switch to use, to be honest i'm bamboozled with information,
    Am i correct in thinking that the faster the rise and fall time the quicker the measurement?
    shall i use the schmitt trigger, totem pole, phototransistor or transistor?
    Thanks!
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    At 100Hz, the period is 10ms. Even if it took 1ms for the photo-detector to turn on or turn off, it would be fast enough.
    What do you have available locally?
     
  3. NornIron

    Thread Starter New Member

    Nov 19, 2013
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    thanks Mike!
    so are you advising not to worry about the rise and fall?
    Also would it be adviseable to use the schmitt trigger version instead of a phototransistor with a pull up resistor?
    Cheers!
     
  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Are you talking about a photo-interrupter like this?
     
  5. NornIron

    Thread Starter New Member

    Nov 19, 2013
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    Yeah, that is a schmitt trigger example am i correct?
    the types i have been looking at are Number1 and like this Number 2,
    thanks for your advice!!
     
  6. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    For your non-critical application, either one will work. The schmitt trigger version has a no-bounce output pulse, which might be an advantage if you are using a counter or uprocessor.
     
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  7. NornIron

    Thread Starter New Member

    Nov 19, 2013
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    I will be measuring measuring the vibration of an unbalanced motor using a pc oscilloscope to determine the frequency! I will order the scmitt trigger version and have a play! thanks again for your advice!
    Kind regards
     
  8. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Are you trying to get a time-varying analog signal, or just a digital pulse every time a slot passes the beam? If you want analog, then get the phototransistor version.
     
  9. NornIron

    Thread Starter New Member

    Nov 19, 2013
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    thanks, either or should suffice, as long as i can accurately determine the speed of the motor, i might just get one of each and have a look, i have wired a simple IR transmitter and receiver which works but is not that accurate due to it not being shielded from day light i think! hopefully one of these will be able to measure the speed!
     
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