High Speed Digital counter

Discussion in 'The Projects Forum' started by Dropout, Nov 8, 2008.

  1. Dropout

    Thread Starter New Member

    Nov 8, 2008
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    0
    Howdy!

    I'm anything but well versed in electronics, but I do have a basic understanding of ....basic stuff. So, I figured I'd solicit those of you who know a lot more than me to help me with a problem...hopefully.

    I've built a digital counter for the purpose of tallying rotations on my metal lathe. The reason I need to do that is that I wind guitar pickups, and the tonal characteristics of a pickup are determined in large part to the number of wraps of magnet wire.

    I made the counter itself from a digital pedometer by removing the mechanical pendulum, and soldering leads from the necessary points on the PCB and connecting the leads to a micro reed switch.

    I placed a strong NIB magnet on the rotating pickup bobbin holder, and by means of a home made holder, placed the reed switch in close proximity to the rotating piece.

    It works, but only until I get to around 150 RPM, then it starts skipping or missing turns. I figured that out by using my built-in digital lathe tachometer and a stop watch to calculate an expected number of turns over a 60 second period at various RPM's.

    I'm guessing that the problem is contact "bounce", but I have no idea how to overcome that with a micro reed switch. I've heard that adding a small value capacitor to the circuit might help, but I don't know where to place it in the circuit (in series or parallel, before or after the switch, etc.), the value.

    Could it be rel;ated to the pedometer's ability to keep up? If so, any ideas on what might be a better device to use? Maybe a calculator?

    I need the counter to keep up at 400 RPM's ideally (the fastest I can safely guide 42 guage wire without it breaking).

    Any help or advice is GREATLY appreciated!

    Thanks
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    Did you ever think of a hall-sensor?
    This is a magnetic sensitive resistor.
    See this page of the EDUCYPEDIA for more info on these sensors.
    http://www.educypedia.be/electronics/sensorshall.htm
    I think there ara sensors that can go upto 3000 RPM.

    Greetings,
    Bertus
     
  3. Dropout

    Thread Starter New Member

    Nov 8, 2008
    4
    0
    Thanks.

    Nope, never heard of those, and I wouldn't know how to use it in this application.

    Thanks again, though!
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Your pedometer won't be able to keep up. Digi-Key has a nice little counter, part #RCL03 that should work for you. It has an internal battery, and costs $32.40. They have a line of counters.
     
  5. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    Here is an aplication note how to use a hall effect sensor.

    Greetings,
    Bertus
     
  6. Dropout

    Thread Starter New Member

    Nov 8, 2008
    4
    0
    Thanks to both of you!

    Guess I'll cut my losses and buy the counter. Maybe use a Hall Effect sensor for a switch if the dry reed switch doesn't work out with the store bought counter.
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Be aware that those counters are either/or. But your reed switch should keep up ok.
     
  8. Dropout

    Thread Starter New Member

    Nov 8, 2008
    4
    0
    Either / or? Not sure what you mean.
     
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