hall sensor

[Joes]

hi there i have a hall sonsor that i woud like to intergrate into one of my project
here is what i have:
http://www.digikey.co.uk/product-detail/en/ATS682LSHTN-T/620-1327-1-ND/2042757

so what i'm trying to do is measure the wheel speed on a vehicle so im stuck to a max voltage around about 12v.

so far i have tried connecting +12v to pin 1 of the sensor and pin 4 to ground through 470ohm resistor which seems to work i get a variation between 6.06 - 9.48 volts on pin 4 of the sensor which also if i connect a 1mohm resistor i can get that down to 2.8 - 4.6 volts to go into the arduino.

i also had a play with running the sensor off a 5v supply and had no joy im presuming thats down to the minimum voltage rating of this sensor compared the the resistor size on the neutral leg. my concern is the 12v supply of the car isnt going to be very smooth so dont know if the sensor will handle some rubbish going down the line to it or do i need to do something to regulate it before?

also im presuming it might be safer to run an octocoupler inbetween the sensor and the arduino or something similar?

or am i completely barking up the wrong tree and does anybody have any better ways of going about this sensor.

any help will be appreciated thanks

[GoForSmoke]

Is there a pattern to the voltage variation you get and does that follow the turning of the gear?

How close do you have the sensor to the gear?

How is the direction detection supposed to work, or is that only to be set up for one way?

[Erdin]

This is the sensor, http://www.allegromicro.com/Products/Magnetic-Speed-Sensor-ICs/Wheel-Speed-Sensor-ICs/ATS682.aspx

The sensor is for 12V, so I suggest to use it with12V.
The resistor on the low side (between the sensor and ground) seems the best option.
You could bring the voltage down with a voltage divider (two resistors).
Perhaps two resistors of 10k.

An optocoupler is a lot better, it also avoids ground problems.
I didn't read how to calculate the value of the resistor, but with a value of 100 ohm or 470 ohm, it should be okay for most optocouplers.

[Joes]

Is there a pattern to the voltage variation you get and does that follow the turning of the gear?

How close do you have the sensor to the gear?

How is the direction detection supposed to work, or is that only to be set up for one way?

yes that voltage range i stated follows the shape of the toothed cog

i have been trying from 1.5- 0.5mm

dont know and doesnt really matter if it works in both directions in this application


ok thanks i am using 3 of these sensor's so i will need a optocoupler with 3 in one but i presume i'll have to go for one with 4 in one does any one have any recommendations on what sort to go for due to pcb design might have to be surface mount?