Converting TTL to Zero Crossing for Speed

Discussion in 'The Projects Forum' started by TXSailor, Jun 14, 2012.

  1. TXSailor

    Thread Starter New Member

    Jun 14, 2012
    I'm building a Speed Sensor for a controls project but my input is a Hall Effect Sensor that already exists. It's a 5V device but when I look at the output it appears that it never returns to zero Volts but outputs a 2.35V signal at zero speed and it goes up to slightly less than Vcc (+5V) when things are moving.

    I was going to use a LM2907 or LM2917 Frequency to Voltage convertor but that chip expects a zero crossing (square or Sine wave).

    What's the easiest way to take the signal I have to work with and get it referenced to a zero crossing


    Is there another approach I should be looking at?

    I really only need to know when a speed has been breached (either going faster or going slower).

    Thanks, D
  2. panic mode

    Senior Member

    Oct 10, 2011
    what is the part number of the hall sensor and is there a datasheet?