variable reluctance sensor/speed switch

Discussion in 'Hobby Electronics' started by stocky, Jul 21, 2003.

  1. stocky

    stocky Guest

    I am building a speed switch around a LM2907, but want to add a "pulse" LED
    that blinks every time the magnet goes past the senor....I'm having a mental
    blank, i'm sure it's easy but can't think how to do it! Should I
    capacitively couple the signal from the sensor, so it doesnt mess up the
    signal goint to the '2907 and use something like a schmitt trigger to flash
    the LED? I know the output amplitude from the sendor varies greatly with
    speed, but I need the LED pulses to make it easy to setup. Ant suggestions?
    stocky, Jul 21, 2003
    #1
  2. stocky

    Dan Hollands Guest

    It is not likely you can drive the LED directly from the sensor - you
    probably need some type of high impedance device like a mosfet to go between
    the sensor and the LED.

    --
    Dan Hollands
    1104 State Road
    Webster NY 14580
    585-703-2963

    www.QuickScoreRace.com
    "stocky" <> wrote in message
    news:uCRSa.7273$...
    > I am building a speed switch around a LM2907, but want to add a "pulse"

    LED
    > that blinks every time the magnet goes past the senor....I'm having a

    mental
    > blank, i'm sure it's easy but can't think how to do it! Should I
    > capacitively couple the signal from the sensor, so it doesnt mess up the
    > signal goint to the '2907 and use something like a schmitt trigger to

    flash
    > the LED? I know the output amplitude from the sendor varies greatly with
    > speed, but I need the LED pulses to make it easy to setup. Ant

    suggestions?
    >
    >
    Dan Hollands, Jul 21, 2003
    #2
  3. stocky

    stocky Guest

    My next thought was do I put the output of the sensor into an opamp and
    drive it to a fixed level square wave, then feed that to the LM2907 and the
    schmitt trigger (maybe via a cap). That would get me around the varying
    input levels. yes?


    "Larry" <> wrote in message
    news:...
    > "Dan Hollands" <> wrote in message

    news:<o5TSa.164294$>...
    > > It is not likely you can drive the LED directly from the sensor - you
    > > probably need some type of high impedance device like a mosfet to go

    between
    > > the sensor and the LED.
    > >
    > > --
    > > Dan Hollands
    > > 1104 State Road
    > > Webster NY 14580
    > > 585-703-2963
    > >
    > > www.QuickScoreRace.com
    > > "stocky" <> wrote in message
    > > news:uCRSa.7273$...
    > > > I am building a speed switch around a LM2907, but want to add a

    "pulse"
    > > LED
    > > > that blinks every time the magnet goes past the senor....I'm having a

    > > mental
    > > > blank, i'm sure it's easy but can't think how to do it! Should I
    > > > capacitively couple the signal from the sensor, so it doesnt mess up

    the
    > > > signal goint to the '2907 and use something like a schmitt trigger to

    > > flash
    > > > the LED? I know the output amplitude from the sendor varies greatly

    with
    > > > speed, but I need the LED pulses to make it easy to setup. Ant

    > > suggestions?
    > > >
    > > >

    > A schmitt trigger would be a good way you will set the on time (LED)
    > and at high speed the trigger would be so fast that you may not see it
    > and as you noted the input loading would be reduced.
    > Hope it helps
    stocky, Jul 22, 2003
    #3

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