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Old 05-07-2010, 11:44 AM   #1
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Default Stock knock sensor voltage output?

Arrrrghhhhhhhhhhh!!!

So how much voltage do you guys see from your stock knock sensor? I am only seeing like 0-.3v Yes, that's point 3. 0.3 Isn't this ****** supposed to put out 0-5v? fukk!

I am running a hydra but it shouldn't matter. volts is volts and the knock sensor plugs right up into the hyudra.
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Old 05-07-2010, 12:45 PM   #2
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I'm not familiar with miatas specifically, but in general a knock sensor is just a microphone. There is usually a "knock box" which interprets that signal and converts it into some sort of higher voltage signal for the benefit of the ecu. I suppose it would be possible to have this circuit integrated into the ecu, but usually it isn’t.
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Old 05-07-2010, 12:52 PM   #3
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Quote:
Originally Posted by faeflora View Post
So how much voltage do you guys see from your stock knock sensor? I am only seeing like 0-.3v Yes, that's point 3. 0.3 Isn't this ****** supposed to put out 0-5v?
Sounds about right. Like therieldeal said, the sensor itself is just a simple analog transducer.

You can't plug a microphone directly into a loudspeaker, right? Gotta have an amp and probably some EQ in the middle. Same deal here.
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Old 05-07-2010, 01:40 PM   #4
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Stock knock sensor also needs a phantom voltage supply.
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Old 05-07-2010, 03:05 PM   #5
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OK, right, well it's not plugged up directly into the Hydra ECU--- it is actually going through the stock wiring up to the factory ECU harness which then plugs into the hydra harness which then plugs into the hydra.

Sooooo in my Hydra readout I'm only seeing these fractions of volts.

If the stock sensor is phantom powered then it would need two power lines, not one
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Old 05-07-2010, 04:41 PM   #6
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No. Microphones using phantom power can have just 2 wires. You can google them.

Look for my knock sensor amplifier thread.
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Old 05-07-2010, 04:49 PM   #7
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Old 05-07-2010, 04:52 PM   #8
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Oh shiz ok. Sooo if everything is hooked up properly, what voltage range should I see?
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Old 05-07-2010, 04:53 PM   #9
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Too small for the Hydra.

Search for my knock amplifier circuit!
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Old 05-07-2010, 05:00 PM   #10
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BALLLLLSSSSSS

OK I will search.

Thing is this **** used to work before I ripped out my old engine and upgraded hydra to 2.6. Voltage at hydra used to be 0-5v proper like. Now it is piddles.
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Old 05-07-2010, 05:46 PM   #11
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Doesn't mean that your sensor isn't detecting anything. I'm sure if you try hard enough you can get it to register a full 5v. With the Hydra you have the ability to set the threshold. So as long as you have the threshold set at a proper level, then it will function as it is designed.
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Old 05-07-2010, 07:18 PM   #12
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Quote:
Originally Posted by JayL View Post
Doesn't mean that your sensor isn't detecting anything. I'm sure if you try hard enough you can get it to register a full 5v. With the Hydra you have the ability to set the threshold. So as long as you have the threshold set at a proper level, then it will function as it is designed.
I just posted up in your hydra knock threshold thread. I'm running 2.6 and my range on that map is .11 to .17 :|
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Old 05-07-2010, 08:08 PM   #13
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Since it's 2.6, then I'm not really sure what to tell you. When you say your range is .11 to .17, are you saying that's what your current threshold is set at or is that the min and max range of that map?
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Old 05-07-2010, 08:50 PM   #14
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Quote:
Originally Posted by JayL View Post
Since it's 2.6, then I'm not really sure what to tell you. When you say your range is .11 to .17, are you saying that's what your current threshold is set at or is that the min and max range of that map?
That is the min and max range of that map. :|
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Old 05-12-2010, 05:42 PM   #15
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Also keep in mind that a knock sensing circuit doesn't go by voltage alone. In fact, a steady 5 volts, if you shorted the knock sensor output to the TPS reference voltage attempting to test things, for example, probably wouldn't trigger it. At the very least, it will look for the signal to be coming in on a specific frequency close to the frequency knock would make. A more sophisticated setup may even only respond if the sound comes in within a set time of the spark firing or have other criteria.
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