Meanwhile I'm working on knock monitoring tool.
Knock sensor is a microphone. At ideal case it produces certain frequency on knock. Ecu picks it up and retard the ignition timing, whereas in real world a gear shift can produce same frequency so ecu look at other parameters as well before considering it as a knock.
Very crucial sensor when it comes to tuning.
Never tune any engine without monitoring the knock.
I made 3 devices in total.
One is an amplifier. Knock sensor is connected to its input and a 3.5mm jack to its output. So you can plug headphones to it and hear it live.
Second, i used a knock sensor as a headphone mic, then connected with the laptop and use Equalizer APO application to filter out other frequencies and focus on only one.
Third, Connect knock sensor to a micro controller and get output on an oled in graphical format.
Here me slightly hitting on the knock sensor.