DIY knock detection, how?

DIY knock detection, how?

Author
Discussion

GreenV8S

Original Poster:

30,150 posts

283 months

Friday 1st July 2005
quotequote all
As far as I understand it, knock detection systems typically consist of a piezo microphone bolted to the block, a band pass filter and some sort of adjustable level detection circuit, all built into the ECU.

What I want is a standalone version that can be fitted to a vehicle that doesn't have the necessary smarts built into the ECU. Either just to display a 'noise' reading that I can look at during testing, or ideally with some sort of alarm output. I've found a couple of people selling diagnostic units for around £250, look like they're aimed at dyno operators rather than something intended to fit a car. Is there a better solution?

dilbert

7,741 posts

230 months

Friday 1st July 2005
quotequote all
How about the Mk I earball.

GreenV8S

Original Poster:

30,150 posts

283 months

Friday 1st July 2005
quotequote all
Eh? What's that you say? Speak up would you?

cyberface

12,214 posts

256 months

Friday 1st July 2005
quotequote all
dilbert said:
How about the Mk I earball.

You got funny shaped ears, innit?

deltafox

3,839 posts

231 months

Friday 1st July 2005
quotequote all
How about an audio amp and a set of headphones so you can hear it?

daxtojeiro

741 posts

245 months

Saturday 2nd July 2005
quotequote all
Hi,
there are several methods of doing this, I have designed a system for Megasquirt that works with the Extra code : http://megasquirt.sourceforge.net/extra/knock.html but if its indication your after then theres this: www.viatrack.ca/
Phil

eliot

11,364 posts

253 months

Saturday 2nd July 2005
quotequote all
Ive got one of Boris's knocksense units on its way to me right now.

Boosted LS1

21,165 posts

259 months

Saturday 2nd July 2005
quotequote all
Peter, I made some using a piezo and a bespoke circuit board with a volume and sensitivity circuit plus a red light. I'll see what parts I have left. I may have the schematics somewhere.

Boosted.

350matt

3,733 posts

278 months

Saturday 2nd July 2005
quotequote all
A rather bizzarre and very cheap method is to run some relativly solid plastic tubing onto the engine ( like onto the end of a stud) and the other end goes into the cabin / outside the test cell and is attached to a large open ended tin can with a pipe soldered to the bottom to fix to the other end of the pipe. The pipe is drilled through to give a hole into the pipe from the can base You can then hear det usually as a sharp crackling noise.

We used this at Cosworth a couple of times would you believe

Matt

GreenV8S

Original Poster:

30,150 posts

283 months

Saturday 2nd July 2005
quotequote all
Thanks for those links.

I've looked at the MegaSquirt info a couple of times and keep coming away unsure whether it capable of doing all the things I need. For example there appear to be multiple hardware versions but the Extra features that the knock detection system is built on don't work on the newest hardware?

Is there an advocacy forum or other resource where I can find out which (if any) MegaSquirt solution fits my problem? (essentially 8 cyl sequential FI, mapped ignition, mapped WI, dual lambda control)

daxtojeiro

741 posts

245 months

Saturday 2nd July 2005
quotequote all
Hi,
the Extra code will only work on the original MS microprocesor, not on MSII. MSII is simply a plug in pcb that replaces the original processor. Both work on the same pcb. Both have mappable spark, fuel and dual ego support, but the extra code has been developed for some time, it now does a lot more than just fuel and spark, it will do water injection too, have a look here: http://megasquirt.sourceforge.net/extra/
neither system does sequential, that is a subject that keeps coming up and no one has bothered with it that I know of, as it just doesnt seem worth the hassle. Maybe MSII will go that way, Ive no idea,
Phil

Boosted LS1

21,165 posts

259 months

Saturday 2nd July 2005
quotequote all
Boosted LS1 said:
Peter, I made some using a piezo and a bespoke circuit board with a volume and sensitivity circuit plus a red light. I'll see what parts I have left. I may have the schematics somewhere.

Boosted.


And I can plug in headphones

stevieturbo

17,229 posts

246 months

Saturday 2nd July 2005
quotequote all
Autospeed did a couple of articles on making a knock detector, basically using a hearing aid amplifier, and you attached a small mic to the block.

Picks up all sorts of weird and wonderful noises though.

Knocklink can be found here, or indeed Im sure plenty of other palces sell them, and is basically the type of thing you want.
www.brdevelopments.com/link.html

Or det cans as some call them, with a piece of tubing attached to the block, then routed into a pair of ear muffs is supposed to be a very good way, although Ive never tried it myself yet.

Pigeon

18,535 posts

245 months

Sunday 3rd July 2005
quotequote all
You want a bandpass filter centred on 5kHz - apparently that's where the knock signal is strongest and most distinctive. (I got that from some SAE paper on ignition timing, so it's probably pretty good.)

GreenV8S

Original Poster:

30,150 posts

283 months

Sunday 3rd July 2005
quotequote all
The link system looks very interesting and I may well give it a try. These systems all seem very expensive though given that one 'bar' from a graphic equaliser display does more or less the same thing.

rev-erend

21,404 posts

283 months

Tuesday 5th July 2005
quotequote all
350matt said:
A rather bizzarre and very cheap method is to run some relativly solid plastic tubing onto the engine ( like onto the end of a stud) and the other end goes into the cabin / outside the test cell and is attached to a large open ended tin can with a pipe soldered to the bottom to fix to the other end of the pipe. The pipe is drilled through to give a hole into the pipe from the can base You can then hear det usually as a sharp crackling noise.

We used this at Cosworth a couple of times would you believe

Matt


Fantastic I know money was a bit tight

Marquis_Rex

7,377 posts

238 months

Wednesday 6th July 2005
quotequote all
Marquis has allowed me to write this on his behalf so don't blame him....

Use a knock sensor bolted to a spare boss on te block, cur the wires and either wire drect to a set of stereo headphones, or into one of those CD to tape converters and you can listen to the 'knock' diretly, you soon get used to what the engine normally sounds like and then what knock sounds like.

The headphones may end up a bit loud or a bit quiet (usually work OK though i've listened to lightweight K's and clunky colognes among others) but using the tape adapter you can adjust your stereo volume to suite!

Learnt this at Cosworth Tech and used it on my own projects with some success ......

FBA2933

stevieturbo

17,229 posts

246 months

Wednesday 6th July 2005
quotequote all
So you are saying this works, with no form of amplifier at all ?

Headphones wired only of a knock sensor ??

Marquis_Rex

7,377 posts

238 months

Wednesday 6th July 2005
quotequote all
He says "Yes"!

eliot

11,364 posts

253 months

Friday 8th July 2005
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My Knocksense unit turned up from Boris today, took a few weeks.