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Old 02-04-2005, 02:23 PM   #1
Lachlan
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Default Electrical Signal Question (EE nerds, please)

Does anybody know the form of the signal that comes off the engine speed wire on the ECU? It seems like if you know it you could get some leds, pots, and whatnot and rig up an easy shift light.
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Old 02-04-2005, 05:53 PM   #2
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Its usually pulsed, so you get 1 pulse for every revolution.

Or are you wanting more info on the pulse width, etc?
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Old 02-04-2005, 05:56 PM   #3
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Yeas, it would be nice to know the width and shape of the pules.
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Old 02-04-2005, 05:57 PM   #4
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i believe its a square wave <if thats the term> on and off i know i was able to emulate the car moving for my revlite shift meter using a hand held square wave signal generator
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Old 02-04-2005, 06:27 PM   #5
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Yes, it will be a square wave. As far as pukse width - I dunno - best bet it to grab a cheap o-scope and have at it.
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Old 02-04-2005, 10:11 PM   #6
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Definately square wave, and definately more than 1 pulse per rotation. Duty cycle is usually 50%. As for how many pulses per revolution of the sensor, well, I dont know, but they vary alot from manufacturer to manufacturer. I've seen as low as 11 pulses per rev up to 40 pulses per rev.

If you feel like it, take yours out of the gearbox, determine which wire is positive, which is ground and which is the signal wire. Apply 5v to the positive, ground wire to negative, and put an LED with 1K resistor from the signal wire to the ground wire. Mark or note a place on the shaft, and turn it slowly 1 rev and count the number of times the Led lights up.
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Old 02-05-2005, 09:34 PM   #7
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It's not a square wave. I have scoped the pattern before, it's an analog sine waveform. Depending on the motor, the frequencly will be anywhere from (6x to about 32x per cranshaft revolution).

And by the way, every Subaru crank sensro I'v seen, from a 2.5na to a 2.2na, to 2.0t motors are all 2 wire sensors. The third wire shown in the diagram is a signal "sheild" that only absorbs and grounds EMI voltages.
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Old 02-05-2005, 09:58 PM   #8
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I havent looked at a schematic. Seems Subaru's solution is the exception to the rule. EVERY one I've ever worked on before was square wave with a signal output wire.
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Old 02-07-2005, 02:09 AM   #9
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Call up raptor performance and check if their shift light will work. http://www.raptorperformance.com/
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