Signal Comparison, output higher

Discussion in 'The Projects Forum' started by jmeager, Jul 25, 2006.

  1. jmeager

    Thread Starter New Member

    Jul 25, 2006
    4
    0
    Hi everyone. Newby here. I am a novice in electronic circuit design but would love to learn.

    I want to create a circuit that can take two ABS sensor outputs, compare them and pass through the higher of the two.
    Prior to the comparison the signals are being passed through a reluctor interface that changes it from a magnetic to a hall effect output. This adapter is already in place and working.

    I need to take these two hall effect signals and send the ECU the higher of the two. The reason for the circuit is a traction control system on my car. The ecu can only receive one driven and one non-driven input. This has the effect, as the non-driven is on only one front wheel - it causes the traction control to behave differently on left versus right hand turns.

    Bosch make the perfect device called the Speed Box 2, but at a cost of 770 Euro, they can go jump......

    What I need to know is how to compare two different square wave signals, and output the higher. Any advice on the type of circuit or chip that may do it would be GREAT!

    Thanks heaps everyone.

    Regards,

    Jeff
     
  2. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
    2
  3. jmeager

    Thread Starter New Member

    Jul 25, 2006
    4
    0
    thanks heaps. Great starting point.
     
  4. n9352527

    AAC Fanatic!

    Oct 14, 2005
    1,198
    4
    Let me ask you one question first, by higher, do you mean the voltage or the frequency? As far as I know, most Hall sensors used in ABS have fixed voltage outputs, and produce square waves proportional in frequencies to the rotational speed of the wheels.

    If yours do not produce frequency, then an analog comparator as suggested above with an analog DPST switch should be sufficient. But if they do work on frequency, then you need something else.
     
  5. jmeager

    Thread Starter New Member

    Jul 25, 2006
    4
    0
    Yes, actually, after looking at the lm339, I don't think it would work. It is a variable frequency - ie as the wheels travel a different arc, one spins faster than the other, and hence the signal increases / decreases.

    So yes, it is a variable frequency that I need to compare ....
    Any ideas?
     
  6. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
    2
  7. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    Look at the spec sheet for a frequency to voltage converter, like the old LM2907. Get two to work identically, and then you can use the voltage comparator to indicate which wheel has the higher frequency.
     
  8. jmeager

    Thread Starter New Member

    Jul 25, 2006
    4
    0
    Thanks very much. The second EDN article looks perfect. All I need to do then is to use the output logic of that circuit to switch between the two signals. I call this fast track your electronics design! (There is a good reason why people go to uni for 4 years to learn Electronics Engineering)
    Thanks again.
     
Loading...