DIY knock tool

Want to build a simple electronic tool for listening for and recording knock using your factory knock sensors?  Frustrated that the aftermarket 'knock boxes' dont really work?  This article is for you.

Supplies you will need:

-3.5mm male microphone jack (same plug as a stereo headphone jack)
-some shielded cable (3 total contacts - typically 2 jacketed conductors plus the shield).  You can use standard headphone cable.  At least 6 feet is a good idea so the cable can easily make it from the engine bay to the passenger compartment.
-a 3 pin bosch/amp style female connector. 
-about 2 feet of standard single conductor wire, 18-20 gauge.
-a ring terminal

to use the tool you will need:
-a laptop pc with a microphone in jack
-a car with a standard 3 pin knock sensor
-(optional) 'race' style headphones with built in speakers and a stereo jack

The wiring should be done as follows.  Use a multimeter to figure out which wire corresponds to the section on the mic plug:

-tip of the mic plug goes to pin 1 of the 3 pin connector
-middle band of the mic plug goes to pin 2 of the 3 pin connector
-base of the mic plug should go to two places: pin 3 of the 3 pin connector and a cable that terminates with a ring terminal that should be secured to an engine bay ground, typically the valve cover or intake manifold.

the cable should look something like this:

example of the headphones I use:

You can record the audio from the knock sensor by using something like windows sound recorder with all the wiring hooked up.  The result should sound like this sample.

Cables are available for purchase from our store here

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