Knock sensing ideas and circuit designs

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davebmw
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Re: Knock sensing ideas and circuit designs

Post by davebmw »

Fred wrote:Dave, if you haven't seen this, you should read it :

http://www.diyefi.org/forum/viewtopic.php?f=35&t=193
Yes i read that quite some time ago, but i can't help but try to pull in some of my own data and see what is there in real time.

I note the requirement for an AGC for the front end this would be easy to do using the tacho output to adjust the front end gain on the fly.

all fairly easy to do with the op amp front end and bandpass filter me thinks. :)
93'BMW 325is M50B25TU, Rebuilt 06/06, JE10.5:1, polish&port. Scorpion BB, K&N CAI, TEJ21 WBO2, '07 M3 Evo 18" 225F, 255R, EBC Kevlar, Bilstien Sprint, Polyflex. Head rebuild Oct'08, OEM+FSE FPR, MS2v3.0_DJB Custom, Extra 2.0.1
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jharvey
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Re: Knock sensing ideas and circuit designs

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Do I recall you had two knock sensors, and plan on capturing it in stereo. So you'll have both signals captured in sync. That will be some nice data to have hanging around. From the scopes web sight, "Be aware, that most microphone inputs are only mono"

Can you also get the noise floor of your vehicle through a variety of RPM's, before the knock.

To bad you don't have sequential control, if you did you could also determine what cyl knocked, and we could post process your audio signals to see if we could determine that with the signals. We should see small amplitude and shift differences between the two sensors.

About the TPIC and such, we could roll our own BPF, energy detector, an integrator, or we could buy it and connect it via SPI. That SPI shouldn't be to hard to do, and it allows for on the fly reconfiguration.

I saw that intersil chip as well. I'd agree it's basically a cut and paste of the TI chip, but I haven't heard of intersil before, so I was thinking more of the TI chip.
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Fred
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Re: Knock sensing ideas and circuit designs

Post by Fred »

Just noticed that you reported this :

http://freeems.aaronb.info/tracker/view.php?id=24

Thought it best to link between the thread and issue as a cross ref.

Fred.
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jharvey
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Re: Knock sensing ideas and circuit designs

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Dave I see you note op-amp filter, I thought I might recommend looking at the LMF100, it's a 4th order BPF as well as many other configs. I've used it before with great results. When I used it, it was used in a fairly wide range of temperatures and preformed very well.

I also see 8th order filters are common place these days, although they appear to be LP not BP. Perhaps higher Q's are possible these days. It's been a small number of years since I've used the LMF100, so it's quite possible that there is better out there now.
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Re: Knock sensing ideas and circuit designs

Post by Fred »

Jared, I believe you need to keep the frequency band quite wide anyway. I guess a steep roll off could still help though :-)
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davebmw
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Re: Knock sensing ideas and circuit designs

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Thanks for the cross reference, I should have though about that :oops: .

Personally I think we should make the whole thing as easy as possible with the least number of components that way more people will want to give it a go and it DIY-EFI will be the site for yet another aspect of Engine Management.
The more ideas we can get on here with some kind of functional proof behind it would be superb.

now after spending 3 hours outside freezing my nuts off trying to get my engine running on MS2 again to do some knock recording if finally give up because of losing the light and it starting to snow!
I put the OEM ecu back in and start her up to put some charge back in the battery the bloody thing won't idle and I think to myself...Has the idle valve stuck open, have i burnt out a couple of coil packs? no it turns out the pipe that goes from the idle valve to the intake manifold has come off! ahh relief! pop her back on and she works fine.

So i didn't get her running for any longer than a minute and couldn't get the mixture ripe for knock but what i have found is that the line input captures the normal engine noise perfectly. and yes the noise floor moves up considerably when you rev up from idle to 3000Rpm.
the sensors even pick up noisy hydraulic tappits!

so the plan for friday now is to equip a second laptop with the scope software as this tuning laptop of mine P3, 333 with a blistering 192MB ram will have a bit of a time trying to run the scope program and MT at the same time.
I don't suppose there is a way to capture the line in on the sound card in MT as a field for logging with the rest of the data???
93'BMW 325is M50B25TU, Rebuilt 06/06, JE10.5:1, polish&port. Scorpion BB, K&N CAI, TEJ21 WBO2, '07 M3 Evo 18" 225F, 255R, EBC Kevlar, Bilstien Sprint, Polyflex. Head rebuild Oct'08, OEM+FSE FPR, MS2v3.0_DJB Custom, Extra 2.0.1
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Re: Knock sensing ideas and circuit designs

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Fred wrote:Jared, I believe you need to keep the frequency band quite wide anyway. I guess a steep roll off could still help though :-)
I don't think the narrower band of a 4th order will be much of an issue.

If the op-amp is set as a sallen-key 2nd order bandpass filter it could roll off at 6db per decade. If set on a center frequency of 6KHz, a 1Vp-p 60KHz signal is down by 6db so about .5Vp-p passing.

However if we have a 4th order, that's 12db per decade, so it's about .25Vp-p and would be .5Vp-p at somewhere around 50KHz.

Really all it does is toss out more junk data. Also my experience with the LMF100 was more stable than the sallen-key.
davebmw
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Re: Knock sensing ideas and circuit designs

Post by davebmw »

sounds like you are the guy to do the filtering then!
93'BMW 325is M50B25TU, Rebuilt 06/06, JE10.5:1, polish&port. Scorpion BB, K&N CAI, TEJ21 WBO2, '07 M3 Evo 18" 225F, 255R, EBC Kevlar, Bilstien Sprint, Polyflex. Head rebuild Oct'08, OEM+FSE FPR, MS2v3.0_DJB Custom, Extra 2.0.1
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jharvey
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Re: Knock sensing ideas and circuit designs

Post by jharvey »

sounds like you are the guy to do the filtering then!
Don't let me fool you... I may be talking out my arse, but don't know it yet.

It's not really that big of deal. The data-sheet for the LMF100 isn't that bad.

Do we know the clock rate we plan to run up on the TA card? How hard is it for that to produce a 6KHz * 50 (or 100) frequency signal. Switch cap filters need a pulsing signal. So 300KHz or 600KHz signal.

We would likely want either the mode 1, or mode 1b setup. Both offer a pair of 2 pole filters cascaded makes 4 poles. Requires 3 resistors for each filter, and of course the chip. Probably wouldn't hurt to have the decoupling cap on the power supply as well.

A proto can be purchased and played with if one feels like it. It can be found at the below link for about $30 to $35. The schematic can be downloaded as well.

http://newenglandqrp.org/nescaf
davebmw
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Re: Knock sensing ideas and circuit designs

Post by davebmw »

Just an idea but wouldn't it be cool if we could program a PIC to perform the filtering and pick out the knock from the noise??

I have an ICD2 programmer at home that I have been dying to use on something but never had the time to sit down and teach myself PICish. That way the parameters could be altered through the serial port the circuit would be much simpler.

Also had a seriously cool thought! when I manage to record engine noise and knock from the sensors I can post it up and anyone can download it and play it back to setup and test their own knock circuit designs.
Obviously it will be different for all engines but we could start an audio profile for different types of engines starting with mine. If knock can be reproduced and recorded, a profile could be created for the signature of knock which could be used on any engine with a little tweaking by programming in the cylinder bore diameter etc to get the resonant frequency of the combustion chambers.

thoughts??
93'BMW 325is M50B25TU, Rebuilt 06/06, JE10.5:1, polish&port. Scorpion BB, K&N CAI, TEJ21 WBO2, '07 M3 Evo 18" 225F, 255R, EBC Kevlar, Bilstien Sprint, Polyflex. Head rebuild Oct'08, OEM+FSE FPR, MS2v3.0_DJB Custom, Extra 2.0.1
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