If you hook the +12 part of the LED to power and then hook the negative end of the LED to the ESC line it shouldn't light up until there is knock.
However these pulses are small in duration and may very well not be seen by the eye.
Plus you would need to make sure that the ESC module can source 10ma of current to run the diode, most likely it can but I don't have the specs. on it.
All the KR detectors and the ECM are high impedance inputs which don't draw much current from the ESC module IE. they don't load it down much with current draw.
Nobody I know puts an LED right on the ESC line to make a detector, it would be an interesting test however since 10ma isn't really a lot of current.
Make sure the diode is rated for 12 volts, available at radio shack, or has the proper resistor in line to only draw about 10ma. of current through it, 600ohms to 1K ohms works usually for most 1-3 volt forward LED's.
The resistor could be placed in series with either leg and the supply or ESC line.
To make a light LED meter you would first need to store the counts of the ESC line and decide how many of those + to - transitions you want to light up the first LED and then the second etc?
Part of the design and the reason you need to somehow correlate the counts to real knock as seen by the engine and ECM management system.
I would assume perhaps 2-3 transitions per LED. Guessing so far.
Then we can build a counter with outputs to LED's and an automatic reset of the counter after a set period of time say 15-25 seconds or so.
Sound reasonable?
I do not know what scheme caspers uses to light their LED gauge but it works just fine in my GN and is well worth the $$$.
Here is a pic. of a two digit 00-99 counts readable counter I am using on my ESC line to try to develop such a correlation.
I can only run about 10-14 pounds of boost on the snow tires however so my car rarely knocks.
I did have to make a reset feature upon powerup which is a simple timer that resets the counts in the chips for 2 seconds when power is applied.
It gets rid of ESC to ECM noise and triggering as well as engine cranking KR.
I haven't incorporated an auto reset feature after counting starts since I want to review the counts and manually reset it with the pushbutton that's on the board.
Works fine but no schmatic as of yet....
The unit is upside down in the picture and the small LED's just read out the numbers on the 7 segment displays in BCD format.
http://a6.cpimg.com/image/CA/D4/56185546-ece4-02000180-.jpg