We can all buy AFR meters, but want to build our own
We can all buy reprogrammed ecus... yet you want to do it yourself.
Now, Im not so good with the elctronics bit, but how about someone works out a DIY Knock Monitor, with flashy lights....get the picture. After all, the Link thingy is bloody expensive, and Im sure the bosch sensor if it has to be used, could be picked up very cheaply on its own, or even second hand somewhere.
Any takers?

 

tadaaaaa.

Well, maybe, I need to do something about getting a knock sensor. I think it's quite simple, basically an amp that filters out all but the knock freq, and the led display is effectively "volume".

can't be too hard

paul

 

OK it's not a DIY one but it's a lot cheaper from Link NZ

 

im sure john looked at this... might be worth emailing him?

 

well, he did buy a knock link

 

Hi Guys,

I started to investigate this - then as with many projects - it got put on hold!

Basically you need a DSP for spectral analysis to look for 6.5 kz spikes - this is approximate for Pre MY96s - & does however change slighly from model to model - car to car - And some mods (as John Banks has just discovered - ie changing your manifold will change the resonant caracteristics of the engine)

Anyway if anyone is interested a really good place to start would be the Texas Instruments TMS320 DSP. This is the most commonly used device by the automotive industry and is designed for this exact application.

There is an Application Note - SPRA039 - That explains the principles and use in some detail - even has some sample code.

Best of luck.

Chris


PS - If you cant find the detail email me & I'll foreward it on.

[Edited by Chris.Palmer - 8/16/2002 11:24:17 AM]

 

DSP?

what would be wrong with a high order active band pass filter?

I am pretty sure this is what the knock link uses.

basically you could then put the out put through a rectifier, smooth it and get a dc voltage to put into a 3914 led display driver.

Paul

 

Has anybody tried a bit of reverse engineering?

Not that I would advocate taking the lid off a product to nick the design of course.

 

Oops I just did.

 

Digital Sound Processor. Ok - may be overkill to display a few flashing LEDs.

However, Knock, has a very distinctive signature, what you propose will work, but a lot of noise - false alarms will ge through too.

The DSP approach - is much complicated - & expensive

I've just had a quick flick through the article again - Explains Knock & Detction theory quite well - its quite an interesting read - (if you're a sad bugger- like me )

 

toltec.. I wouldnt but would be interested

Drop me a mail with your findings, if you dont post here!

David

 

Hi all,

AFAIK the Knock-Link just uses an op-amp as a bandpass filter, see Op-Amp Basics for some background.

Also look at this page for some interesting and practical knock sensor background.

Andrew...

 

I was thinking of this, but was relying on Delta Dash and the ECU which worked great until the manifold.

Got a knocklink because it is standardised and proven on Subarus. MRT would not send one. Scoobymania did not carry stock and didn't know when they would. BRD had it in stock Performanceexhausts.net say their price is about half this WITH the sensor I since heard.

I would have nothing to compare with otherwise.

It has helped me so much with mapping it is great. Wish every car I had mapped one - extra peace of mind if the ECU decides not to play.

So the knocklink is very simple, and for a lot of people with JECS remaps probably not very helpful if the ECU setup is working. In my case it wasn't, but many are a bit "deaf" when it comes to hearing detonation - especially if they don't know what to listen for, or even a bit older with high frequency hearing loss (!) so a Knocklink can be very useful or at least peace of mind.

 

you've sold me on it JB!

I think a decent knock sensor should give me enough tools to map my car, now I have the WB afr sensor, and basic select monitor tool to give load, rpm so i can compare with map.

probably open it when I get one and see what makes it tick.

paul

 

Paul... Want to test all this on my car after I get back off holiday??? Ill buy an emulator...

Ill Drop you a mail when Im back from spain.

David

 

oooh crikey, I don't usual go further north than northampton! Is there anything up there? will I be safe?

sounds like a plan.

paul

 

Just got in contact with Jamie. His prices are a tad better than others I have seen. Ordering one next week. The DIY was a good idea while it lasted. Sometimes I just get too impatient.