racerex

Sorry, I just couldn't help myself with the whole AC/DC thing (I know, I'm retarded)

Anyway, I just completed my home made knock monitor. I have not had a chance to take any pics, but I will try to tomorrow. It turned ou pretty good and was easy and cheap to make.

All I did was use an elctret microphone from radio shack and soldered up a pretty simple preamp and voltage reducer so that I can just tap off the car battery. Then I bough one of those fm transmitters that are used if you add a dvd player or the like onto your car and don't want to upgrade your radio.

The microphone is hot glued onto a clamp that you can just clamp to the block. Then you just tune into 89.1, adjust the volume and your ready to tune the ignition.

It seems to work, but I need to adjust the sensitivity and get real familiar with the sounds so that I can readily recognize knocking as it takes place.

BLUEHATCH

Sounds like a good idea... post some pics...

TekPhobia

So what's the station's jingle? "You're listenin' to KNCK...piston slap in the morning, knock in the evenin'"

-Tim

Ghetto88ZC

haha thats great. Post some pics and tell us how it worked out. Thats some ghetto fabulous thinking.

racerex

Ok, here are some pics. The romulator in the back has nothing to do with anything. The little aluminum box has a pot in it to scale down the voltage from 12 v to about 5v. It also contains the preamp circuit for the microphone.


The black box is the transmitter. It is powered by 12v and is intended to be used with dvd players installed in cars so that you don't have to hard wire them in.


Here is the mic. It is hot glued to a clamp that attaches to the block. Vibrations carry through the metal and transmit nicely.


Does it work? Yeah, it works, but I need to get it tweaked just right. I'm going to mess with the voltage in order to adjust the sensitivity of the mic. I am also picking up some interferance likely because of a ground loop problem. I am considering just using a 9v battery to power the preamp or wiring in some sort of a coil (like the ones that can be used with head units to reduce interferance--XPLOCIVIC, have you got one of those laying around?)

Now, as soon as I get my ecu chipped (hopefully next week) I can get some dyno time and advance my timing until I begin to hear knock or preignition and back it off a couple degrees from there.

leed

Big thumbs up dude, nice work!

I was planning on doing something similar, but just use head phones. Blasting that ---- through your stereo should work well also. I can only imagine what passengers must think...

racerex

I figure I'm into this about $30 at this point, including the exorbitant shipping charges on the transmitter I bought off ebay.
I think it's a worthwhile investment and besides, I like doing crap like this, it keeps me from getting bored.

Oh. and screw the passengers, if they don't like listening for knock as much as I do, they can drive in their own cars!!

blundar

nice work man. You could probably improve your device substantially by a couple of minor (and not so minor) tweaks:

1. put a crossover in between your pre-amp and your radio transmitter. Filter out all high frequencies (anything above 4000 hz would be conservative). Knock usually occurs at a very low frequency compared to the frequency of engine noise.

2. connect up a wire to the neg terminal of your coil to measure a tach pulse signal. use the tach signal as a the frequency to feed a variable frequency bandpass filter. Filter approx. 1/4 octave above and below your tach signal. This will reduce direct engine noise. I believe there is actually a TI chip that is pretty cheap (<$6) that does this more or less automatically

nice work so far!

projekteg

you lost me at hello

racerex

When you say filter a quarter octave are you saying to use the rpm signal in hz, and go 1/4 octave from there?

So in other words if the signal is 3000 rpm than set the bandpass for 1/4 octave above and below 3000 hz?

This would be the not so minor tweak.