Reading wheel speed – automotive application

I am looking for suggestions on a sensor to use to measure the rotational speed of a wheel. I have pretty much narrowed the choice to a magnetic hall effect sensor, primarily because of the low cost. My plan is to attach the magnet(s) to the inside surface of the wheel hub and fabricate a bracket to hold the sensor. The requirements for the sensor would be: 1. This is in an automotive environment, so the sensor must be robust, able to withstand temperatures up to 60-70 deg C. 2. Must be able to accurately read speeds from 5 rpm up to 2000 rpm. 3. I am using an Arduino Uno R3 ATMEGA16U2 board. 4. I do have ‘C’ programming experience, so (hopefully) that will be no problem.

Just wondering if anyone has done this, or something similar, and what sensor did you use? Thanks, Charles

To which part of the car are you going to attach the Hall sensor? You really can't mount it to the vehicle chassis since the vehicle suspension would constantly throw off the close alignment required by Hall effect sensors. How large and heavy will the magnet be? You may need two to prevent unbalancing the wheel. The cable from the sensor to the Uno will have to be shielded and be able to withstand constant flexing.

Buy a cheap wheel speed sensor that is already proven and used on millions of production vehicles. There are different types but the two most popular are hall effect and magnetic pick up. Generally speaking if it has a 3 wire connector it is a hall effect. I agree with using a hall effect as the mag pick ups are a little more challenging to work with. You will need to bias the sensor signal wire with a pull up or pull down resistor (depends on the sensor you chose), 4.7Kohm usually works fine. Find the schematic and wire it up.

Design your mount.

Write your code.

A wheel is a very harsh environment with continuous vibrations and water, dirt and chemicals thrown up from the road. Not to mention the carelessness of tyre technicians when you get a puncture.

Is it not possible to sense the speed somewhere away from all that - maybe on the inboard end of a propshaft?

...R

Most modern vehicles have an ABS systen - just pick a signal of the built-in hub sensors.

Allan

allanhurst: Most modern vehicles have an ABS systen - just pick a signal of the built-in hub sensors.

The username suggests to me a pre-ABS car.

...R

I think all Corvettes have an open driveshaft. Even those with IRS. Fasten/glue a magnet on opposites sides of the drive shaft. Need balance. Use a sensor to detect the magnets. Compute the wheel RPM based on the differential gear ratio and the sensor count per second.

Paul

Due_unto: To which part of the car are you going to attach the Hall sensor? You really can't mount it to the vehicle chassis since the vehicle suspension would constantly throw off the close alignment required by Hall effect sensors. How large and heavy will the magnet be? You may need two to prevent unbalancing the wheel. The cable from the sensor to the Uno will have to be shielded and be able to withstand constant flexing.

The suspension is from a 1994 Corvette. The back side (inside) surface of the wheel mounting plate, the plate that holds the 5 wheel studs, can readily be accessed. The magnets used with the sensors that I am looking at are very small, about 12mm in diameter and 3 mm thick, and I would be mounting 5 magnets, one at each wheel stud, so there would be no imbalance problem.

Paul_KD7HB: I think all Corvettes have an open driveshaft. Even those with IRS. Fasten/glue a magnet on opposites sides of the drive shaft. Need balance. Use a sensor to detect the magnets. Compute the wheel RPM based on the differential gear ratio and the sensor count per second. Paul

Robin2: A wheel is a very harsh environment with continuous vibrations and water, dirt and chemicals thrown up from the road. Not to mention the carelessness of tyre technicians when you get a puncture. Is it not possible to sense the speed somewhere away from all that - maybe on the inboard end of a propshaft? ...R

I do all my own work, so tyre technicians are no worries. I need to monitor the speed of two wheels, one front and one rear, so I can compare the wheel speed to determine the amount of rear wheel spin. The suspension I am using has reluctor wheels and ABS sensors, but they are the older two wire sensors and are not accurate below 10 MPH.

The picture below is an example of the hall effect sensor and magnet that I am considering. Just wondering if anyone has used one of these, or similar. |500x408

Wheel studs being steel will deflect the magnetic flux.

It is possible to attach a magnet to the back side of some hall effect switches.

This enables the "lost or missing tooth" used in auto ignition and the like.

Hall effect then detects the close metal.

You can see details of this on the Allegro site.(makers of hall effect devices)