racerex

Hey, I'm in the process of designing a knock monitor. I will have a microphone next to the #3 cylinder that I will use to tune the ignition timing by monitoring for knock.

First of all, I need to create a power supply for the mic, so I need to scale down the 12 v supply down to about 5v.

Then, I am using a condenser microphone (the ones you buy from radio shack) and I need a schematic to of some sort of pre-amp to use with the mic so that I can have an output through an 1/8" jack.

I will plug that jack into an fm modulator that I have. That way I will be able to use the car radio to tune into the knock monitor.

Can anybody help me with some schematics?

TekPhobia

Make sure you're using a piezo mic. Second, you're going to want a bandpass filter targeted at around 3kHz. This will be kind of tricky. You're not going to be able to do it by listening to it. Well...you can, but it's much more difficult. The way ECUs do it is they know the position of each piston and then it starts listening soon after ignition for a resonate frequency (around 3kHz) which would indicate knock.

If you do a little Googling, you'll find some schematics/descriptions. Here's one:

http://www.california.com/~eagle/knock.html

Or, continue my search:

http://www.google.com/search?num=30&...o+%2Bschematic

-Tim

Reddy

http://www.autospeed.com/cms/article.html?&A=0353

racerex

This was originally recommended to me by a local hondata tuner and I think it's a good idea.

I will be using the same microphone that this guy is using, but rather than using the headphones, I have an FM transmitter (like the modulators that CD changers use) that will broadcast this so that you can just listen to the motor through the radio.

We'll see how this all works, but I think should turn out pretty good.

BTW, I've been told that after I have wideband tuned the fuel tables to advance the ignition timing tables until I begin to hear the signs of detonation, then to retard it 2 degrees from there.

ShadowRex

just a suggestion why not set somthing up that at 3khz it just triggers a led?

TekPhobia

Problem is....when you're hearing detonation...that's detonation. Pre-ignition can be a silent killer and easily punch a nice hole in your piston. Only something that's listening to the block will pick it up. I imagine it'll be hard to do by ear when you're boosting and the roar of your engine fills the cabin.

-Tim

Reddy

I don't need headphones to know my car sounds like I'm driving through a rainstorm of marbles

accordepicenter

Good thinkin... this is HMT, open downpipe is not the exception, its the rule

racerex

ok, I finished it:
https://www.homemadeturbo.com/forum/...threadid=18800