Hall Effect Crankshaft Sensors  - Page 1
Forum section: electronics / projects

author: GoStags
author_rank: Newbie
timestamp: February 10, 2024, 10:50:44 am
content: A bit of reverse engineering! I have bought a couple of different Crankshaft sensors (BMW types) which have 3 pins, and which I believe to be Hall sensors. They have a built-in magnet, and are supposed to output a digital signal with frequency proportional to the change in magnetic field strength from a toothed steel wheel.I want to interface these with an engine ECU that can receive the digital signal, of 5volts or 12 volts.Not having or being able to find any info on the pin designation, I have tried all combinations to identify the correct one to get a digital output to no avail. The 3 pins are supposed to be as follows: Power, Ground and signal. I have also tried using a pull-up resistor in case the output is 'open collector' to no avail. When placing a piece of steel to it, I can get a small response from one sensor where one wire changes state between 0.7 volts and 0.1 volts approx but cant get at least 5 volts by any means.For those not familiar with automotive digital hall sensors they comprise a permanent magnet, a hall sensor, followed by a high gain amplifier, then a Schmitt trigger at the output.Have I missed something in my attempt to get an output?

author: Benta
author_rank: Super Contributor
timestamp: February 10, 2024, 11:23:59 am
content: "they comprise a permanent magnet, a hall sensor, followed by a high gain amplifier, then a Schmitt trigger at the output."Are you sure? I've also seen types where amplification and signal processing is done in the ECU.

author: jpanhalt
author_rank: Super Contributor
timestamp: February 10, 2024, 11:36:22 am
content: Have you tried Google?https://www.bimmerforums.com/forum/showthread.php?2341402-Cam-sensor-wire-colorsI know that's obvious, and it is not intended to insult.One question is whether "BMW" types change with the model year. Information for newer cars seems to be harder and harder to find. Wiring diagrams for cars 10 years old are available. Would a company intentionally change the pinout?

author: GoStags
author_rank: Newbie
timestamp: February 10, 2024, 11:54:11 am
content: Benta: The other type of crankshaft sensor is the VR or variable reluctance type. The output signal is analogue, and varies with frequency of the magnetic flux. At low frequencies the signal is very small (compared to digital signal) and so requires differential signal amplification and conditioning in the ECU, and is susceptible to noise pickup in the cables.These VR sensor are usually 2 pin but some are 3 pin to include screening connections. I do have one of those and it seems to respond well to a signal from a toothed wheel. But I would prefer a Hall sensor digital signal to avoid noise pickup and the extra signal processing required.Jpanhalt: Yes I have spent hours Googling to no avail.

author: jpanhalt
author_rank: Super Contributor
timestamp: February 10, 2024, 01:52:30 pm
content: Do you have access to the connector for the sensor? A nearby "auto recycler" has been invaluable for getting connectors and pigtails. Customers are allowed to browse and collect their own parts. The price is usually something like a $5 bill, which seems high when the scrap price for the whole car is about $200 locally, but it is very reasonable considering what it would cost from a dealer.If you can get a pigtail, that might help, as the link I gave mentions fairly standard color codes.

author: GoStags
author_rank: Newbie
timestamp: February 10, 2024, 01:56:11 pm
content: Quote from: jpanhalt on February 10, 2024, 01:52:30 pmThanks that might be worth a try.

author: Benta
author_rank: Super Contributor
timestamp: February 10, 2024, 08:41:29 pm
content: Quote from: GoStags on February 10, 2024, 11:54:11 amYes, I know the inductive types. But I've also seen Hall sensors without on board processing (as opposed to Hall ICs, which is what you refer to).