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Old 02-08-2009, 01:54 PM   #1
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Default knock filter and amp

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.
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Old 02-08-2009, 02:33 PM   #2
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Do you still need the GM electronics (as described here:MS2-Extra Hardware Manual) to make the MS (MS2 in my case) acknowledge the knock or is the circuit alone enough (sorry, I am no expert in electronics - I suppose a look at the circuit would tell me )

Thanks
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Old 02-08-2009, 04:55 PM   #3
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thx Jason.
What is the value of C9?
Why is the pink part, uhm, pink?
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Old 02-08-2009, 05:43 PM   #4
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C9 is a trim capacitor, a placeholder, if one were to hand trim the circuit to peak at 13 kHz.

The pink part is because I was cleaning up the schematic and the stupid Orcad software crashed, and lost my work; I saved a screenshot and the pink part is when you select a group of parts. I was in the middle of a move operation.
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Old 02-08-2009, 05:45 PM   #5
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Quote:
Originally Posted by Zaphod View Post
Do you still need the GM electronics (as described here:MS2-Extra Hardware Manual) to make the MS (MS2 in my case) acknowledge the knock or is the circuit alone enough (sorry, I am no expert in electronics - I suppose a look at the circuit would tell me )

Thanks
I'd have to see the MS knock input circuitry.
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Old 02-08-2009, 08:42 PM   #6
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OK I'll re-ask my question here...

What's needed to share the sensor between the factory ECU and hydra?
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Old 02-08-2009, 10:38 PM   #7
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Remove R19.

Does the Hydra take a GM style knock sensor instead of the 99's?
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Old 02-08-2009, 11:03 PM   #8
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Quote:
Originally Posted by JasonC SBB View Post
Remove R19.

Does the Hydra take a GM style knock sensor instead of the 99's?
it plugs into my stock sensor
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Old 02-09-2009, 12:49 AM   #9
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So why do you need this circuit?
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Old 02-09-2009, 03:52 AM   #10
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Quote:
Originally Posted by JasonC SBB View Post
I'd have to see the MS knock input circuitry.
I hope this is sufficient:

From the MS2 Manuals:

A conditioning module is also required, such as GM's Electronic Spark Control (ESC) module (PN 16022621, 16052401), see above. These are also available as Standard Motor Products LXE6, LXE7, and LXE9. These are very common in recycling yards, they were used all virtually all GM vehicles from the mid-1980s to the late 1990s. You should match the sensor and module by application to ensure they will work together properly.

The ESC module sends a voltage signal (8 to 10 volts) when NO knock is detected by the knock sensor. If knock occurs, this signal is pulled low.



This signal is fed to the MS2-Extra ECU via either Pin 3,4,5 or 6 of the db37 connector (SPR1,2,3 and 4 respectively) and linking that pin to either JS4 or JS5. However you need to reduce the module signal voltage since it is too high for the processor port directly. You can use the proto area on the V3 main board, a 1K Ohm resistor (1/4 or 1/8 watt), and a 4.7 Volt Zener 1W diode (Digi-Key 1N4732ADICT-ND, 36) to do this, as shown below:



Is this enough information for you?

Thanks again...
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Old 02-09-2009, 11:20 AM   #11
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No, I need the input circuitry that the line "megasquirt" in the first diagram above goes to.
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Old 02-09-2009, 11:36 AM   #12
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Quote:
Originally Posted by JasonC SBB View Post
So why do you need this circuit?
Quote:
Originally Posted by y8s View Post
OK I'll re-ask my question here...

What's needed to share the sensor between the factory ECU and hydra?
I dont know that I do need the circuit. I just dont know what the ECU(s) are expecting to see from the knock sensor. Is it just a sensor-generated signal or is it a biased resistor?
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Old 02-09-2009, 02:03 PM   #13
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Over on MS forums, there are some implementations of knock chips.. Single, real time programable chips for reading knock.

The downside to them is most need something to speak SPI to them, though a $2 atmel chip will work.. it means you need to find code.

Two things MS is not going to do for you, now, is ignition windowing (only looking when you expect knock, so you can increase sensitivity, prevent "silent knock" death) and have an adjustable level (at least on MS-II beta. The released version supported analog knock signal, which should be a huge boon to anyone, relaxes the constraint on the band pass filter jason posted, and lets you be more sensitive down in your torque peak where you'd expect knock).

You might add an LED output, that's probably the best feature of my knocksense. :-)
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Old 02-09-2009, 02:13 PM   #14
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The MS is logic-level. It expects a low-impedance (to ground) when knock is present, and a high impedance (or +5) when there is no knock. Typically, the output is also held low for a few tens of milliseconds so the MS has time to capture it.
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Old 03-09-2009, 03:27 PM   #15
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Possibly on the MS-I. And now on the MS-II, as well. It still goes into an analog in, but is read as a digital signal. Thanks once again for making more effort to make a product worse.

Whatever. How can you not give up on something like that. You should see what they did to support the guy who made an auto-trans controller out of a microsquirt.

Knock should definately be read analog. Meh.
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Old 03-09-2009, 06:18 PM   #16
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Quote:
Originally Posted by Joe Perez View Post
The MS is logic-level. It expects a low-impedance (to ground) when knock is present, and a high impedance (or +5) when there is no knock. Typically, the output is also held low for a few tens of milliseconds so the MS has time to capture it.
So it doesn't have a programmable "background noise voltage" vs. RPM setup?
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Old 03-12-2009, 05:09 PM   #17
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They have Knock, or no knock.
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Old 04-09-2009, 03:28 PM   #18
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Quote:
Originally Posted by JasonC SBB View Post
C9 is a trim capacitor, a placeholder, if one were to hand trim the circuit to peak at 13 kHz.
Did you actually build the circuit? I'm planning on trying it out once I get the MS up and running, but how would I tune it / determine the value of C9?
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Old 04-13-2009, 01:51 PM   #19
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I'm really curious to see how this works, as well. It seems a good idea, but... knock sensing seems to be one of the harder things to pull off.
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Old 04-13-2009, 05:09 PM   #20
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Quote:
Originally Posted by f_devocht View Post
Did you actually build the circuit? I'm planning on trying it out once I get the MS up and running, but how would I tune it / determine the value of C9?
Yes.
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