Electronic Solutions for Motorsport

Knock Detection – Variable ECU Signal/LED Brightness

3 min read

A new feature in the KSC3 knock detection system is a variable output to the engine ECU and to external 12v led (for variable brightness). This article explains how the feature works.

KSC2 – Previous Model

The previous model to the KSC3 (the KSC2) had a fixed output when knock was detected. The KSC2 would output a fixed 4.5volt+ signal to an external ECU, if the user had one wired in, and a fixed 12v signal to power an external 12v LED.

While this was useful, both visually when driving and when analysing datalogs after, if a conservative correction was put into the ignition map, for example 7-degree retard if knock signal received by the engine ECU, there is a big drop in power even if the knock threshold was only exceeded by a small amount.


In the KSC3 the outputs are now variable from 1-20 points above the set volume threshold.

More the 20 points above the threshold, the full signal is sent to the engine ECU and the LED.

1 point above the volume threshold sends the lowest signal to the ECU and LED.

10 points above the threshold will be half signal and so on.

While driving, the variable signal allows the driver to have an idea of how bad the knock is.

The datalog from the engine ECU will also show how bad the knock was according to the KSC3, not just that the KSC3 detected knock.


The “Test” function will output a cycling 2.5-5volt signal to the engine ECU.

While the LED will cycle from minimum brightness to 50% full brightness.

By logging the signal going to the engine ECU while the KSC3 is in test mode the calibrator can see the signal range.

And by observing the brightness of the pulsing LED, when the KSC3 is in test mode, the calibrator/user/driver can understand what a small breach of the threshold looks like all the way up to 50% maximum LED brightness when the threshold has been exceeded by more than 20 points.

By logging the ECU input from the KSC3, the calibrator can alter the correction map accordingly.

It’s recommended that the minimum voltage pulls the maximum desired retard at the start of the calibration. And when the calibrator gets a feel for the KSC3 output, adjust the correction table accordingly.

For example, to start with the 2.5volt signal from the KSC3 may be set to retard ignition timing by 5 degrees. After familiarisation with the KSC3, the 2.5-volt signal could/may be seen to be safe to alter the retard down to 1 degree for 2.5 volts, 2 degrees for 3 volts, 3 degrees for 3.5 volts and so on. This will be a process of tuning by the calibrator.

Output Duration

It’s important to remember that when knock is detected the voltage outputted to the LED and engine ECU will remain the same for 2 seconds.

eg if after once second of knock getting detected the knock gets worse, the variable output from the KSC3 will remain the same.

The output is the same for 2 seconds after which it will analyse the knock signal again and if knock is detected again, send the variable LED and ECU output again, with a voltage/duty cycle according to how much above the intensity threshold the signal from the knock sensor is.

The output from the KSC3 is variable but it will only change the output voltage to engine ECU/PWM duty cycle to LED, every 2 seconds.

Do not expect the KSC3 to continue increasing the output if knock is detected on the fly, for example every half a second. It will not. The variable voltage will only change evert two seconds, if knock is detected.

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