LM2907 circuit for trigger wheel discrimination

Discussion in 'The Projects Forum' started by DonTZ125, Jan 7, 2013.

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  1. DonTZ125

    Thread Starter New Member

    Dec 22, 2008
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    Good morning! Long-time lurker, first-time poster.

    I'm trying to develop a circuit to read the trigger wheel on my motorcycle for use with a MegaSquirt-based ignition. There are 3 teeth of 5deg width, and one tooth of 36deg width. All leading edges are at 90deg to each other. The leading edges would be the primary signal, telling the ECU how fast the crank is turning; the one long tooth tells the ECU which tooth just passed the sensor. A diagram is attached below.

    My current thought is to use edge detection and two LM2907 chips. By feeding the 'leading edge' signal to one LM2907, I get a baseline reading. The trailing edge signal is sent to a second LM2907, and what I'm hoping is that the sudden increased period from the trailing edge of a 5deg tooth to the trailing edge of the 36deg tooth will be interpreted by the LM2907 as a sudden reduction in frequency, and thus a reduction in output voltage. The two output voltages would be sent to a comparator, and if the second voltage suddenly drops significantly, then a secondary signal is sent to the ECU.

    I'm satisfied with the control scheme from the MS standpoint; what I'm hoping for is commentary on the LM2907 aspect. Is this a reasonable expectation of how the device would work? I've looked around for LM2907 models for LTSpice and found one or two (including the one unearthed by Sgt Wookilar) - but I can't figure out how to model the trigger pulse pattern! :confused:
     
  2. DonTZ125

    Thread Starter New Member

    Dec 22, 2008
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    ... and I can't edit my post to correct the name "Sgt Wookie" - sorry ...
     
  3. spankey666

    Member

    Nov 30, 2011
    91
    3
    have you fuel injected the bike or re you just using the mega squirt for ignition ?
     
  4. DonTZ125

    Thread Starter New Member

    Dec 22, 2008
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    Ignition first, injection later. One thing at a time ... :D
     
  5. spankey666

    Member

    Nov 30, 2011
    91
    3
    i wouldnt bother with FI, although my experience is only with the 3tj 400 which the 600 is based on, flatslides and airbox mods will give better results, we could get 90+ rwhp from a 400 :)
    back to your issue, the "tits" on the fly wheel help balancing and counting is done in the ecu, as you are using a megasquirt, just remove the smaller "tits" and re-balance the rotor, the igniting can then be retarded from software without the need to count . if you are intent on going down the FI route, fit a cam sensor (which is needed for FI) and then you wont have to worry about the 3 small ones. for an easier option in programming, zeeltronic ignitions are the biz and far easier to work with, then just use megasquirt at a later day for the FI.
    for throttle bodies have a look here the web site is having probs atm, but they are trying to get sorted . I work with these guys :)http://www.atpowershop.co.uk/catalog/index.php
     
  6. Georacer

    Moderator

    Nov 25, 2009
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