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Old 09-09-2009, 11:54 AM   #21
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To answer Zaphod's question, there needs to be an additional "AM type detector" circuit between my circuit and the MS, and it sounds like the above-mentioned GM circuit functions as such.
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Old 12-16-2009, 06:42 PM   #22
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Quote:
Originally Posted by JasonC SBB View Post
The circuit is meant to emulate a GM style tuned piezo knock sensor. It is meant for ECUs that can take a piezo knock sensor signal.

You take a 99/00 knock sensor, it filters and amplifies the signal. It is tuned to 13 khz IIRC, which is the peak frequency that I noticed when I did audio recordings of knock from my 00 sensor.

Would it work properly with a Bosch wideband sensor? Or OEM wideband Miata sensor only?

What is the recommended minimum power rating for the resistors? (If one is trying to stuff it in as small packaging as posible)

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Old 12-16-2009, 07:53 PM   #23
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What does the Bosch sensor take for phantom power?

If you give me a datasheet I can tell you for sure.
2nd best would be an existing schematic for the front end of one -such as the old Link, which IIRC, uses the Bosch wideband.
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Old 12-16-2009, 09:17 PM   #24
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Quote:
Originally Posted by JasonC SBB View Post
What does the Bosch sensor take for phantom power?

If you give me a datasheet I can tell you for sure.
2nd best would be an existing schematic for the front end of one -such as the old Link, which IIRC, uses the Bosch wideband.
here's a pdf of the datasheet

http://www.bosch-motorsport.de/pdf/s...knock/KS-P.pdf

What would your filter/amp increase the max output voltage of the 1v Bosch knock sensor to? Or would it?
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Old 12-17-2009, 04:01 AM   #25
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The bosch sensor is a piezo non-resonant sensor. (No need for phantom power).

Therefore remove R19.

However I have to look at the size of the signal to decide if the "gain" of my circuit needs to be reduced.

Last edited by JasonC SBB; 12-17-2009 at 04:18 AM.
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Old 12-17-2009, 04:17 AM   #26
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Anyone have the miata knock sensor datasheet? I vaguely remember its signal is 1/30th of the GM resonant senors though...
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Old 12-17-2009, 03:52 PM   #27
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Quote:
Originally Posted by JasonC SBB View Post
Anyone have the miata knock sensor datasheet? I vaguely remember its signal is 1/30th of the GM resonant senors though...
I can't find the msm knock datasheet anywhere.

Are you saying that the above circuit boosts a 0-0.033 volt signal to a 0-5v signal?
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Old 12-29-2009, 08:23 PM   #28
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Quote:
Originally Posted by JasonC SBB View Post
The bosch sensor is a piezo non-resonant sensor. (No need for phantom power).

Therefore remove R19.

However I have to look at the size of the signal to decide if the "gain" of my circuit needs to be reduced.
This is what John at J&S says about the output difference between the Bosch and the GM resonant ones:

"The output of a resonant sensor is about 500mv/g, while that of a non resonant sensor is about 20mv/g.
An example of a non resonant sensor is the Bosch sensor, which requires a shielded cable."
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Old 12-30-2009, 12:28 AM   #29
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Hmm, that doesn't tell me the difference between either of them vs. the miata factory sensor, which is what I need to know.

I will guess that my circuit is in the ballpark. Its output is designed to mate with the AEM which I presume is designed for the resonant sensors, and its gain is close to 20x, and the bosch sensor is 1/25th the output of the resonant sensors.
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Old 01-02-2010, 10:48 AM   #30
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Maybe these can help

Last edited by WestfieldMX5; 01-08-2010 at 01:36 PM.
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Old 03-05-2010, 05:17 PM   #31
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?
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Old 04-06-2010, 01:08 PM   #32
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Hmm
http://expresspcb.com/ExpressPCBHtm/SpecsMiniboard.htm

The can do 3 pcx 3.8" x 2.5" boards for $51 + shipping sent out the next day.
Each one would probably fit 3 of the circuits, maybe more, so you get at least 9 for $51.
All we need now is someone to lay it out in their free software.
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Old 04-06-2010, 04:39 PM   #33
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They are certainly not the only house which turns boards cheap. :-) I did a set of ~7x4" boards maybe 11 of them for $150? At least I didn't have to do it in their software.

So this circuit just does the filtering/amplification - i.e. no analog levels out, no RPM or angular dependent filtering?
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Old 04-06-2010, 10:47 PM   #34
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Yep, just need a simple bandpass filter, perhaps adjustable with a simple pot to vary bandpass frequency a bit. Adjustable gain is probably not a big deal but it would be nice. Output signal should be low so it does not overdrive the Adaptronic's input.
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Old 07-06-2011, 03:48 PM   #35
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digging this back up for a couple reasons.



The latest MS3 alpha firmware has experimental knock sensor and windowing settings.

To reconfirm, this circuit provides a 0-5V amplified, bandpassed knock signal from the stock NB sensor, correct?
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Old 07-06-2011, 04:46 PM   #36
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Yes, but the output is an AC knock signal, with the same amplitude as a tuned piezo sensor.

I would like to point out that the center frequency should be moved from 13 khz to 6.5 kHz. Higher RPM knock is more centered at 6.5 than 13 khz.

To change it quadruple the sum of the values of C9~C11, and approximately halve R20 and R21.
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Old 07-06-2011, 05:29 PM   #37
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AC knock signal? as opposed to what?
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Old 07-06-2011, 05:44 PM   #38
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Quote:
Originally Posted by y8s View Post
AC knock signal? as opposed to what?
Presumably as opposed to the binary 0 or 5v signal produced by the KnockSenseMS or the 0-10v signal produced by the original GM ESC module on which the MS's knock sense feature was originally based, which conveys a simple "knocking" or "not knocking" indication, rather than merely acting as a bandpass filter and amplifier as this circuit does.

In other words, the Megasquirt's knock-sensing capability is rather primitive. It is not able to read an analog signal (even one that's been filtered and amplified) and do the comparison to determine whether or not knock is present on its own. It needs to have an external device do the hard work, and then simply send a binary signal to the MS telling it whether or not knock is present. (At least, that's how it is on MS1 and MS2. I assume MS3 is the same.)
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Old 07-06-2011, 09:21 PM   #39
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Correct. (1st paragraph)
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Old 07-06-2011, 10:35 PM   #40
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ok but the AC is all happening from 0-5V... which sounds like what I'm after.

Here is the new knock settings dialog:



and if windowing is desired:



note that you can output the window to external knock devices for some reason.

Quote:
Originally Posted by [email protected]
On/off vs. analogue:
The only circuits presently described provide an on/off yes/no type input. So for anything existing, this is what you need.
The analogue option allows you to feed in an analogue 0-5V signal that represents signal intensity. You can't just connect this to a raw knock sensor - you need to amplify it and utilise bandpass filters. A chip such as TPIC9101 does this but requires SPI to control it too. This analogue option is more for future development work.
A TPIC9101 does not show up when I google so therefore it doesn't exist to me.
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