ABS sensors

[Jon K]

Yeah try the scope again - they may have changed it on the new cars but all of the models I've messed with so far have had VR sensors in the wheel position. If you go to hall you will need a really good sensor - theres so many teeth on the bmw wheels (at least on the ones I am seeing) so you would need a hall sensor with really high switching frequency.

[mefmotorsport]

Yeah try the scope again - they may have changed it on the new cars but all of the models I've messed with so far have had VR sensors in the wheel position. If you go to hall you will need a really good sensor - theres so many teeth on the bmw wheels (at least on the ones I am seeing) so you would need a hall sensor with really high switching frequency.

Yes, I remember 12 years ago when I had a Stack dash and a hall effect sensor on a Subaru ABS ring. the speedo worked fine up to about 70mph then it just fell to pieces, the Stack unit or the Hall effect sensor couldn't cope with the frequency. I think the Subaru has 44 teeth on the ring, a quick fix was to grind off every other one! I cant do that with the BMW as they're inside the wheel bearing.

Martin

[stevieturbo]

Yeah try the scope again - they may have changed it on the new cars but all of the models I've messed with so far have had VR sensors in the wheel position. If you go to hall you will need a really good sensor - theres so many teeth on the bmw wheels (at least on the ones I am seeing) so you would need a hall sensor with really high switching frequency.

Yes, I remember 12 years ago when I had a Stack dash and a hall effect sensor on a Subaru ABS ring. the speedo worked fine up to about 70mph then it just fell to pieces, the Stack unit or the Hall effect sensor couldn't cope with the frequency. I think the Subaru has 44 teeth on the ring, a quick fix was to grind off every other one! I cant do that with the BMW as they're inside the wheel bearing.

Martin

If the signal is compatible, then the speedo correction thingy would work. It can reduce or increase the pulses by 100% either way, in increments of 1%

And if it accepts a VR signal, and outputs something more akin to a square wave....kill two birds with one stone ?

[mefmotorsport]

I'll try and do some tests today, I have just got a spare front hub which has the sensor fitted so it is easier to play with off the car! I'll scope the output wires and see if there's any visible signal. I seem to remember doing this with the ones on my C2 but without success. The C2 ones were definitely active devices, I even got some documentation about them from someone on 22B, I think they were Seimans devices, I did have a full technical document but I chucked it out recently!

Have a look here at this data sheet, This is what I'm on about! This one may not be spcifically the BMW one but it gives you the right idea. Looc at the diagram near the bottom showing the operational configuration. It's a 2 wire device with the +ve supply going on one wire, the other going to earth via a load resistor that is in the ecu, the output signal is taken from that :http://www.datasheetcatalog.org/datashe ... 57_pra.pdf

It's showing a 12v battery supply (27v zener diode to limit any voltage spikes) and a 75 ohm load resistor so the signal would be quite small. I'll give this setup a try and see if I get anywhere.

Martin

[mefmotorsport]

Having now studied that Data sheet in the link above, I'm convinced that this is how the BMW ones, and also the Citroen C2 ones work. It may be possible to make some kind of amplifier/signal processing to convert the 7/14mA current signal in the 75 ohm resistor into a suitable 5V one. I bet most modern cars use these things now.

7mA across the 75 ohm resistor represents 0.525V, 14mA represents 1.05V so I could use this to switch a transistor on and off. With a load resistor in its collector up to a 5V rail then that should give me a 5V pulse for the ecu.

Martin

[Antral]

Eh. Mmmmm. I think you may be loosing a lot of people here Martin, is it summat to do with grid bias. LOL.

[mefmotorsport]

It's no good, some pulses come out at certain intervals when the wheel is stationary (as per the data sheet), looks like its far too clever for it's own good! certainly for the DTA wheel speed application.

Looks like I'll have to find a suitable hall effect sensor such as the RS one with the M12 thread that will fit in the BMW mounting hole or even use a VR sensor and that little PCB to convert it to a digital signal.

[Jon K]

Martin - that stinks. They should have stuck to the VR sensors they used!

Can you post an image of the wheel/sensor? I was on another forum and found a great thread on making some small hall sensors. I will post when I find it.

[mefmotorsport]

This one if off an E92 M3 front hub, it's made by "ATE"

Martin

[mefmotorsport]