Bicycle computer pickup question

Discussion in 'The Projects Forum' started by wayneh, Sep 30, 2010.

  1. wayneh

    Thread Starter Expert

    Sep 9, 2010
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    I think most bicycle computers use a magnet moving past a reed switch to detect revolutions. Is this right, or do some use the magnetic pulse (zero cross?). To get to the point: How might I supply a an alternative signal to the cycling computer's input that it will recognize?

    If I can get that to work, it'd be a very inexpensive data acquisition logging device that is also small and portable.
     
  2. Markd77

    Senior Member

    Sep 7, 2009
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    I've got 2 cheap cycle computers and they both use reed switches - you can hear them if you put a magnet near them.
    A mosfet could replace the switch and maybe work.
     
  3. wayneh

    Thread Starter Expert

    Sep 9, 2010
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    Maybe. There must be some polarity to the two contacts, and a tiny current flowing when the reed switch closes. Supplying a square wave thru a high ohms resistor might fool it, if I can figure out which side is "ground". I'll see if I can read anything on the DVM.
     
  4. John P

    AAC Fanatic!

    Oct 14, 2008
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    An opto-isolator might do it too. Would it be an advantage to separate the computer and driver electronics?
     
  5. wayneh

    Thread Starter Expert

    Sep 9, 2010
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    Separation would alleviate my main concern about experimenting - inadvertently zapping my cycling computer. I believe I've got an old opto-isolator in my parts drawer, so I'll take a look at the datasheet.
     
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