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  #11  
Old 10-24-2020, 02:19 AM
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Is Pin nine a square wave sine wave what is it
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  #12  
Old 10-24-2020, 06:55 PM
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Originally Posted by andrewwynn View Post
Is Pin nine a square wave sine wave what is it
No I don’t think that it is. I am pretty confident it’s a sine wave signal. At any rate, although I could be wrong, square waves don’t seem suitable to measuring/reporting data on something as variable as engine speed.

However, I can’t confirm first hand if it is a sine wave signal on pin #9. I can only say that I read on another forum (from someone who tested it using an oscilloscope) that it is. What I can confirm firsthand is that it works perfectly with a device that needs a sinusoidal tach signal.

Last edited by Frankiesayrelax; 10-24-2020 at 07:09 PM.
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Old 10-24-2020, 10:23 PM
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Originally Posted by Frankiesayrelax View Post
No I don’t think that it is. I am pretty confident it’s a sine wave signal. At any rate, although I could be wrong, square waves don’t seem suitable to measuring/reporting data on something as variable as engine speed.

However, I can’t confirm first hand if it is a sine wave signal on pin #9. I can only say that I read on another forum (from someone who tested it using an oscilloscope) that it is. What I can confirm firsthand is that it works perfectly with a device that needs a sinusoidal tach signal.
My guess is a square wave. Every simple tachometer input on aftermarket systems is looking for a simple square wave signal.
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  #14  
Old 10-24-2020, 11:09 PM
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Originally Posted by Overboost View Post
My guess is a square wave. Every simple tachometer input on aftermarket systems is looking for a simple square wave signal.
Sounds right to me. Why make it a sine wave with varying frequency? A square wave makes more sense, pulsing at each rev.

I know that up to around 2004 most Porsches used a 12V square wave on pin 9 of the OBD2 for the tach signal. But not for 2005+. Found this pic on the intertubes (pelican) from an early Porsche Boxster, as an example.

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Great find and documentation there, @frankie!

Glad you got your problem solved and thanks for letting us know. I bookmarked your post, just in case...
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  #15  
Old 10-25-2020, 12:08 AM
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Originally Posted by Overboost View Post
My guess is a square wave. Every simple tachometer input on aftermarket systems is looking for a simple square wave signal.
Then I stand corrected! At any rate, all I know is my shift light works and reads (and displays) rpms perfectly! So I’m a happy camper.
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  #16  
Old 10-26-2020, 10:54 AM
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Originally Posted by Frankiesayrelax View Post
Yahhhh, definitely (a tad) insulted that you would suggest I would skip right past something so obvious and comparatively simple as reading the instructions and a wiring diagram, and come straight to xoutpost. Actually, there was no instructions included specifically on wiring for the tach signal (personally, I haven’t mastered the art of reading instructions which do not themselves exist!)

Anyway, I first acquired a pin out for each dash cluster connector (from a BMW specialist mechanic) and found that the “TD” wire of the CAN bus was not suitable for the device I’m using, which requires a sinusoidal wave signal (the CAN Bus signal then must not be sinusoidal or otherwise is not suitable for my application in some way). So, after the wiring diagram failed to produce a suitable tap-in point, and the manufacturer couldn’t tell me which signal it was for my specific vehicle (no surprise there), I went back to the internet with a suspicion that the OBD II port (as was suggested above) would be my route (if TorquePro or OBD Fusion could get RPM data from my engine, so should I). A couple of days later I managed to find a BMW related OBD port pin out that showed pin #9 on the OBD connector was a tachometer signal. (Furthermore, I’d read, on another forum, a thread where someone had used an oscilloscope to confirm this very wire’s signal was sinusoidal) I tapped into that wire and low and behold my shift light works flawlessly. And this after even BMW mechanics told me I wouldn’t be able to do it on a “CAN bussed” vehicle, which just goes to show you, where there’s a will there’s a way.

Here’s the Pin out that I used (apparently, applicable to all BMW models after 2000:

1 - +12V (ignition, in run or start)
4 - Chassis Ground
5 - Signal Ground
6 - CAN high J-2284
7 - ISO 9141-2 K-Line (engine, ISO-9141 and ISO 14230, automatic transmission diagnostic)
8 - ISO 9141-2 K-Line (IKE/KOMBI, ABS, ABS/ASR, ABS/ABD, ESP, DSC, Airbag and other electronic equipment)
9 - TD/RPM
14 - CAN Lo J-2284
15 - ISO 9141-2 L-Line (of ISO 9141- and ISO 14230-4)
16 - +12V (battery power)
SOLID info here! Thanks for updating this thread

reps sent
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