Reverse Polarity Of Hall Effect Sensor To Invert Output signal

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4 years 8 months ago #31884 by rome83
Hey guys, not sure if I should be posting this in here as this is one of my first ever posts. Wondering if anyone knows if I can reverse the polarity of a hall effect sensor to invert the output signal.

The background story is, I had a 2006 VW Golf 1.9L Turbo Diesel come in for a service and hard to start issue. Checked it and confirmed hard to start. Checked for codes and found CMP implausible signal fault. I got the scope out and checked the power and ground which was good. Then checked the CMP signal output and it was horrible. I pulled off the top timing cover to check the tone wheel on the cam and it was in good condition. I pulled out the CMP and checked it with a screwdriver and it wouldn't hold a signal properly so confirmed the CMP sensor was faulty. Due to money constraints, the customer wanted an aftermarket replacement. The issue is when I was looking, some of my suppliers said there were two types, a long cable version and a short cable version(the one in the car was a long cable version). My main supplier only had the short cable one in stock and assured me it was right but couldn't tell me why or what the difference was between the long and short cable sensors. So I took their word for it and now I'm second guessing myself - because the new short cable is a pull down sensor where the old long cable sensor in the car was a pull up sensor. When new short is plugged in, the 5v Bias voltage on the signal line stays at 5v and pulls down to ground when sensing teeth, whereas the old long cable plugged in, grounds the 5v bias immediately and pulls up to 5v when sensing teeth. I put the new short in to start it and same hard to start issue and same code comes back right away. Now I'm stuck because I don't know 100% if it's the right sensor and I need to be sure before I can look elsewhere otherwise it will be in the back of my mind.

What I want to know is if I switched the power and ground inputs to the sensor, would it invert the signal to make it back to a pull up sensor like the original long cable type? Not sure if I can do that and don't want to take the chance without asking someone first in case I bust the new sensor.

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4 years 8 months ago #31894 by Tyler
Hey rome83! The short answer is... I don't know? :silly:

Based on my understanding of Hall effect sensors, I don't think you'd end up inverting the signal. At best, I think you'd end up with an inoperative sensor. As an example, I grabbed the info sheet for an Infineon Hall switch:

www.infineon.com/dgdl/Infineon-TLE4963-2...bac4015287edd79f27ca

I don't know if that's how YOUR sensor is wired, but it's probably similar. Nothing in this diagram suggests it'd invert it's signal if you swapped power and ground. :(
The following user(s) said Thank You: Andy.MacFadyen

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4 years 8 months ago #31911 by Andy.MacFadyen
The model I have my head is to think of a Hall-Effect as a relay or switch ---- a pull-down type would be equivalent to N.O. Normally Open contacts and a pull-up would be NC Normally Closed contacts.

As with a switch reversing the wires won't change the operation.

" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)



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