DIY Det Cans (DIY electronic knock sensor)

Been considering building one of the homemade knock sensors, was wondering if anyone had some tips and tricks to share? Going to keep this to a small budget of around $30-40. I like a cheap radio slack micro phone device modified to use a battery post clamp, this way I can move it around to listen to various parts of the engine, or frame/chassis. Reason why is the GN is picking up a lot of false knock, no amount of tuning will mitigate the issue. I.E. no boost, low boost, low timing, etc. Still gets knock at the same rpm every time, Im thinking it may be the noisy lifters or the down pipe touching the frame when the engine torques up in the engine bay. If I can build one and route the signal to my laptop, I can probably use the EQ to filter out some of the noise too?

Looking around for ideas...

http://www.realhomemadeturbo.com/for...?topic=22257.0

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

i built my own from a jaycar electronic personal amplifier kit .the alarm clock disc speaker is too sensitive so have gone back to the mic that was in the kit
http://i852.photobucket.com/albums/a...ps2149d780.jpg
http://i852.photobucket.com/albums/a...psf3f58720.jpg

Are you satisfied with the operation of the device? Anything you would change to make it operate better? Are you able to filter certain frequencies?

the kit had a frequency switch and volume .i used sheiled cable seams to work good you dont really need filtering the splat sound of detonation stands out.i did at one stage just use the mic input of my lappy in passthrough mode and could record as well worth a try just making a mic cable and clip and trying the laptop

Tagging this thread for future reply regarding some technical documentation I need to find regarding the filtering circuits and the frequency range of the typical knock sensor.

If you use the same kit with a knock sensor there's no mistaking knock when it happens.