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Knock sensor 0V

EFI Wiring Fundamentals

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Discussion and questions related to the course Motorsport Wiring Fundamentals

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Hi all,

I am attempting to wire up a Motec knock sensor to a Motec M150. The data sheet calls for signal and 0V. The M150 has dedicated terminals for various knock sensors, but I can't tell if these terminals are intended to work with specific 0V terminals (as the 5V/0V groups work). Can I use any 0V terminal for knock? My dealer mentioned wiring a pair of knock sensors as "differential", but he didn't explain what that meant...

Thanks in advance.

Since there is no reference supply for knock sensors, you can use any of the 0V pins. To wire as differential, you use Knock1 / Knock2 for Differential 1, and Knock3 / Knock4 for Differential 2.

Thanks David. Can you explain more on wiring as differential? Why do that? How would I do that? Pardon my ignorance, but I don't see anything in the M150 data sheet or hardware manual about this.

A knock sensor is essentially a microphone, so there is a voltage differential between signal+ and signal-. By using two knock inputs instead of one ground and one input, you can effectively increase the signal range that can be supported, as well and decrease the noise floor.

Try googling "Differential vs. Single Ended signaling" to learn more.

If you configure a "Knock Cylinder 1 Resource" to use "Differential Knock 1", then when you using Help->Firmware Wiring, you will see which pins are using for the Differential Knock signal. This is the only documentation I am aware of.

I think the firmware feature to support this came after the hardware reference manual was written (which was more than 10 years ago)

Thanks guys. When you set the Knock Cylinder 1 Resource to Differential Knock 1, the firmware wiring shows that knock 1 is the "positive" and knock 2 is the "negative". Similarly, for Differential Knock 2, knock 3 and knock 4 are the positive and negative (respectively).

Back to back testing with a 2 wire Bosch sensor has not shown a difference in operation with the wires swapped.

Thanks Stephen. I kind of figured as much, but good to have the confirmation.

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