Saturday, 12 March 2016

One from the workshop: DIY-knocksensor

In order to detect detonation, modern cars use knock sensors to sense detonation and adjust the ignition accordingly. Partially for performance reasons, but mainly for emission reasons the more advance you can put on an engine, the better are the emissions going to be.

That said, a knock sensor is basically a microphone tuned for a very specific band of frequenties. Now in order to analyze the data gathered via the knock sensor very clever electronics and software are required and even then, it's usability is restricted to vehicles, which run roughly the same bore and stroke.

Now, detonation if heard via an engine stethoscope makes a very distinct sound (it's not called pinging/pinking) without a reason. So the basic idea was to run the input from the knock sensor through a simple mono-amplifier and listen to it in real-time via headphones.



Parts:
1) knock-sensor from a car (the one depicted is intended for a Nissan NV200 and lots of other cars)
2) EV1-injector-plug adapter/repair cable (cheaper than buying the EV1-plug alone)
3) a cheap (most likely Chinese) amplifier board. You could go stereo, but the cheapest mono will do. The one depicted is a TD2030, which can take straight 12V-DC or AC
4) two headphone jacks and at least one headphone/microphone plug
5) a 12V-power-source (in my case a cigarette-lighter-plug-adapter)
6) bit of wire, solder, etc...

First step, solder the microphone jack onto the EV1-plug's cable. I used black as ground and grey as plus on the plug. (As it's a microphone it doesn't really matter.)

Fit it all in a box...
 ... plug in the sensor and run the two cables to the "in"-connector.
And a set of headphones to the "out"- connector.

So, how well does it work. Quite brillantly actually. As I didn't have a bike to test it on, I tried it out on my car (old Mercedes Diesel) and you could actually hear the injectors opening, the camchain rolling on the sprocket and the hydraulic lifters making some noise.
I have to admit I am really curious how well it will perform on the turbo bike to tune the ignition!






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