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TPIC8101 knock sensor interface

Daniel Sofer
Prodigy 90 points
Other Parts Discussed in Thread: TPIC8101

Dear Sirs,

 

My name is Daniel Sofer, and I am a newcomer to the forum.

I am head of development at DSA, a technology firm in Brazil, specializing in developing alternative fuel engine management systems.

As part of a work in progress, we need to implement a very careful knock sensing sub-system.

I found out about the TPIC8101 and purchased a few hundreds to start working with them in numerous trials, some of them in test vehicles.

However, I have been unable to get it to do what i would like it to: sense knock.

It does seem to operate very much like the data sheet says it would, except that:

   a) analog output shows integration regardless of input frequency, or even absence of input signal. Output just varies with integrating window width;

   b) SPI output does mirror input, but chip seems not to enter "advanced SPI mode";

The advanced mode not being reached would not really bother me if it menat only that SPI output would not be available, as we intend to use analog output. However, it is not clear to me if advanced mode is required to get the chip to operate. Nor is it clear why it does not enter advanced mode, as the command for it to do so is sent and correctly mirrored back, thus received.

I would very much appreciate any help on this subject.

Kind regards.

Daniel Sofer

DSA

  • 0
    TI__Guru 73830 points

    Daniel,

    Thank you for considering the TPIC8101 for your knock sensor application. We will try to help with your setup problems so that you can detect knock in your engine. The device has to be tuned to detect a specific knock signature using the SPI interface and parameter tables in the datasheet. We use an input frequency to help emulate the knock and setup the device. You will need to know the the characteristics of your knock sensor the set it up properly.

    The analog output will show integration whenever a waveform is present on the input. What you are looking for is that the integration waveform reaches a specific voltage level at the end of the integration window. If the frequency is too high or too low, then the integration waveform will terminate early or over shoot. I will attach a tutorial that I have used to help train people to use the device.

    I have not had a problem with entering advanced SPI mode as long as the proper bit sequence is entered during normal SPI mode.

    Please review the attached document and maybe it will help clear up something and let us know if you continue to have problems with the device.

    Best regards

    Tom Cosby

    Applications Engineer

    Mixed Signal Automotive

    TPIC8101 Training.pdf
  • 0 in reply to ThomasCosby
    Prodigy 20 points

    Tom,

    Can I interface TPIC8101 on both types of knock sensors (resonant and flat response)?

    Best Regards

    Carlos Milhor

     

  • 0 in reply to carlos milhor
    TI__Guru 73830 points

    Carlos,

    The TPIC8101 only works with the resonant type knock sensor. We do not offer a device that works with the non-resonant type.

    Best regards

    Tom

  • 0 in reply to ThomasCosby
    Prodigy 90 points

     

     

    Dear Tom,

     

    I did try out the example provided in your material, which actually did not differ substantially from what I had tried out previously.

    The reuslts are still the same.

    I enclosed a few images from what I've been able to capture.

    First, the SPI. The bit sequence sent is the following:

    byte 1: 0x0046      -  01000110

    byte 2: 0x00E1     - 11100001

    byte 3: 0x002A     - 00101010

    byte 4: 0x00A2     - 10100010

    byte 5: 0x008A      - 10001010

    byte 6: 0x0071      - 01110001

     

    The result is in the first image. The problem may rest in the fact that we continue to see a perfect mirrorr of the sent bits, which I understand means I am not being able to get the part to enter into advanced SPI mode.

    However, the operation would appear normal, if we look at the second image. The yello trace is the CS, the cyan is the INT window, the green one is the input frequency and the purple one, the output. Here, we just have a low analog result, lower than expected, but qualitatively, everything seems to be in place.

    The problem is that output remains unchanged when input signal is switched off, as can be seen in the third image.

    As for your reply about the type of knock sensor I, too, was unaware that the flat response type could not be used. Can you, maybe, elaborate on why? And, if used, what would the results and faults be? By the way, presently I am still trying to get it to respond to a signal generator, so the type of sensor cannot be at the root of the present difficulties.

    But I would have intended to use a flat response type on our acutal systems.

    Thanks in avance

     

    Daniel Sofer

    Director of Engineering

    DSA Ltda

  • 0 in reply to Daniel Sofer
    TI__Guru 73830 points

    Daniel,

    I tested your setup and do not get those results. It may be better to work this out over the phone. 

    Please send your contact information to me at t-cosby@ti.com.

     

    Thanks

    Tom

  • 0 in reply to ThomasCosby
    Prodigy 70 points

    Daniel,

        Did you manage to get device into "Advanced SPI mode"?

    I am experiencing the same issue.

    David.

  • 0 in reply to David Sobon
    TI__Mastermind 21800 points

    David,

    Just to close the loop on the forum.

    See this thread for entering Advanced SPI mode issues:

    http://e2e.ti.com/support/applications/automotive/f/26/t/150591.aspx

    John