Hall effect sensor testing

Discussion in 'The Projects Forum' started by PatrickTBuckley, May 5, 2009.

  1. PatrickTBuckley

    Thread Starter New Member

    May 5, 2009
    Hi -

    This is my first post - after reading some of the information provided on this site I am somewhat intimidated...!

    My problem: I have a Ford GT40 replica that uses a Smiths Electronic speedometer....the speedo has never worked, I have substituted another speedo head and have removed the speedo and the Hall effect senor from the vehicle and set up a test bench.

    I am getting 0.01 v as an output from the sensor - I suspect that this is the cause of the problem but want to make sure that I am testing the sensor correctly....

    Do I have to have a pull up resister in order to test it correctly?

    Thanks for your help!
  2. bertus


    Apr 5, 2008
  3. premlx

    New Member

    May 6, 2009
    Yes this is likely an open collector device and would require a pull up resistor, typically limiting current to max of 20mA. Also you will need a magnet to excite the sensor into changing state. Some speed sensor use the Hall sensor as a "geartooth" sensor, in which case there is already a bias magnet behind the sensor (molded into the plastic). You can check for this with any ferrous metal. If this is the case you will need to rotate a suitable gear at a fixed gap (2-3mm, not more) away from the active face of the sensor. If there is no magnet molded into the sensor then it most likely needs a south pole of a magnet or alternating south and north poles from a "ring" magnet. most speed sensing inputs look for a uniform 50% duty cycle signal.

    for more detailed info look at http://www.melexis.com/Assets/Hall_Applications_Guide__3715.aspx it should help.