Knock module for MS3 (beta test)

[savagerocco]

So, are we gonna get anymore info about this? What kind of sensors will it support? I can't wait for this upgrade!

[y8s]

So, are we gonna get anymore info about this? What kind of sensors will it support? I can't wait for this upgrade!

In retrospect, I should have asked this question prior to sending my paypal!

[elaw]

There are really only two general types of knock sensors... resonant (less common) and nonresonant (more common). Depending on the component values James selected, I'd expect nonresonant ones to connect directly. Resonant ones tend to have higher output and might require a series resistor. Or might not.

The types of sensor can often be distinguished by appearance. Most nonresonant sensors look like this:

...although the conector might vary or there could be a wire incorporated.

Resonant sensors usually have metal bodies and look more like an oil-pressure switch.

[savagerocco]

Well, Eric an I both have two of those hagning out on our blocks just waiting for something like this to hook them up to... I guess I have a third resonant one too.....

[masterx81]

The readout is via an analog pin or via spi communication? On the pdf of the tpic seem that the adc output can be read via i2c (so a pin can be freed)

[jsmcortina]

The readout is via an analog pin or via spi communication? On the pdf of the tpic seem that the adc output can be read via i2c (so a pin can be freed)

It uses SPI already, an earlier iteration had the analogue pin too, but I deleted that. The module is using +5V,0V, SCLK, MISO, MOSI, CS, window. Which is the bare minimum.

James

[masterx81]

That's so nice & clean! Thanks!
The pin used for CS can bee freed up on the cpu if there is only one device in the spi 'chain', leaving pulled up the cs pin on the knock board?

[jsmcortina]

That's so nice & clean! Thanks!
The pin used for CS can bee freed up on the cpu if there is only one device in the spi 'chain', leaving pulled up the cs pin on the knock board?

From memory the chip needs it as part of the command sequence.

James

[masterx81]

Some spi chips work also with the cs always active (pulled down), but on the pdf of the tpic on the timing charts it's always present... worth a try to see if it work wothout it?

[AbatelliCristian]

Hi James,
why you don't use port "inj2" for windows? frequently is unused...

[jsmcortina]

The way it is designed only one single jumper wire is required to interface with the MS3. (In addition to the two knock sensor inputs.)

James

[djp0623]

Can't wait! I installed one of the above style sensors on my block a while ago. I'm glad I did.

[bubba2533]

What pin on the db37 connector can the knock sensor go to?

I'm just wondering if it will work with the current pins I'm using.

[Reverant]

The TPIC8101 only works with the resonant-type knock sensors. It doesn't work with flat response sensors.

[masterx81]

The TPIC8101 only works with the resonant-type knock sensors. It doesn't work with flat response sensors.

The knock sensor is only a piezo microphone, i not see why it must not work with flat response sensors. The 3rd order bandpass filter is here to filter unwanted frequencies...

[elaw]

Hey... I just wanted to share an idea I had for anyone that's going to use this board. Where the sensors connect to the Megasquirt, I'm going to wire in a 1/8" (3.5mm) stereo audio jack in parallel so I can tap into the sensors' output either for det cans or recording.

[masterx81]

I always map advance with hearphones, amplifier and knock sensor (installed on any car >1990 ca)... I trust my ears more than any sensor.
IMHO this circuit is useful only as an emergency solution while driving, but it not a substitute a good map...

[Matt Cramer]

The TPIC8101 only works with the resonant-type knock sensors. It doesn't work with flat response sensors.

The knock sensor is only a piezo microphone, i not see why it must not work with flat response sensors. The 3rd order bandpass filter is here to filter unwanted frequencies...

We used a flat response sensor in our testing.

[Reverant]

The TPIC8101 only works with the resonant-type knock sensors. It doesn't work with flat response sensors.

The knock sensor is only a piezo microphone, i not see why it must not work with flat response sensors. The 3rd order bandpass filter is here to filter unwanted frequencies...

The TI datasheet says so. And so did a TI engineer in the TI support forums.

[masterx81]

AFAIK there are other interfaces that uses this chip with flat response piezo wothout any problem, and i'm not able to find anything about this on the datasheet. Can you point us where we can find this info on the pdf?
The only problem i can see with non-resonant knock sensors is that the amplitude of the signal is smaller than a resonant one, so gain must be high, input stage (resistor) must be chosen to not attenuate too much, and maybe use a small integrator time constant. Maybe we are a little bit on the edge, but i not see too much problems...
For sure would be nice a table where is possibile to configure gain and integrator constant depending on the rpm...