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[2woody]

On Omega B, the ABS ecu generates the speed signal used by the speedo, stereo, etc., etc

does anyone know what the speed signal actually is ?

My guess is that its PWM, but I don't know the on/off ratio vs road speed.

might it be in some stereo information for example ?

I'm fitting an alternative ABS system to a car of mine and need to still drive the speedo

[TheBoy]

The MID stuff implies pulses per kilometre, in the region of 24000 pulses per km.

[Kevin Wood]

I could probably put a 'scope on it to check.. If I could drive while operating one.

[05omegav6]

39240ish pulses per mile with 245/40/18 tyres. Standard 225/55/16s about 38900 ppm, 235/45/17s nearer 40k

[Kevin Wood]

39240ish pulses per mile with 245/40/18 tyres. Standard 225/55/16s about 38900 ppm, 235/45/17s nearer 40k

Do you get more pulses when "south of the river"?

Any idea of the signal amplitude? Guess it could be 12v or 5v..

[05omegav6]

Pass hardly ever go 'north'

The BLRT wire for the speed signal is relatively substantial, so would guess at 12v but that is a pure guess.

Easiest place to tap it is probably at the sunroof plug just behind the interior light

[zirk]

Would this be the same signal that drives the Non DBW Cruise Unit, often wondered what would be needed to fit a Mig Cruise Control on another VX car without ABS?

[Kevin Wood]

Would this be the same signal that drives the Non DBW Cruise Unit, often wondered what would be needed to fit a Mig Cruise Control on another VX car without ABS?

Yes, I believe so.

[2woody]

wow - that's cool. I didn't hold out much hope of getting this.

Kev, would you like a doctored sensotronic relay with a wire poking out ?

I really need the shape and on/off ratio for the pulses, on the assumption that its PWM. So yes a scope is the way forward.

Same signal as used in the cruise control.

For reference, I'm adapting an Omega B to use the early Teves ABS system, as per Jaguar and Range Rover. This uses an electric pump and reservoir, rather than the crappy Omega vacuum servo for its motive power.

I'm also assuming that a very simple pic-based box'o'tricks will give me the signal I require.

[Kevin Wood]

wow - that's cool. I didn't hold out much hope of getting this.

Kev, would you like a doctored sensotronic relay with a wire poking out ?

I really need the shape and on/off ratio for the pulses, on the assumption that its PWM. So yes a scope is the way forward.

Same signal as used in the cruise control.

For reference, I'm adapting an Omega B to use the early Teves ABS system, as per Jaguar and Range Rover. This uses an electric pump and reservoir, rather than the crappy Omega vacuum servo for its motive power.

I'm also assuming that a very simple pic-based box'o'tricks will give me the signal I require.

Yep, I guess the steering ecu is the easiest place to pick it up.

Would be happy to do a bit more experimentation, and can make PIC based boxes of tricks if required.

[Marks DTM Calib]

Its not PWM, its a frequency which relates to the speed.

[2woody]

Its not PWM, its a frequency which relates to the speed.

that's kinda what I mean. And kinda not

If I go down the pic route, then what is the width of the pulse vs the non-pulse ?

[Kevin Wood]

Its not PWM, its a frequency which relates to the speed.

that's kinda what I mean. And kinda not

If I go down the pic route, then what is the width of the pulse vs the non-pulse ?

That would need a 'scope on the signal to answer, although, in all likelihood, it wouldn't actually matter as most devices would trigger on the positive (or negative) going edge of the signal and not be affected by the pulse width / duty cycle.

[Marks DTM Calib]

No idea on the Mark:Space ratio although as Kevin states, any input would be edge triggered (via an approriate RC plus protection diode circuit).

If working via an interface circuit then the volts will not be so important as the device input is likely to be a 3V part and the input circuit can easily be designed to support in excess of this (use the pulse signal to sink current and use a diode plus internal pull up - simples).

For info, if it was PWM then the width of the pulse would by related to the speed rather than the frequency 

[2woody]

For info, if it was PWM then the width of the pulse would by related to the speed rather than the frequency 

Mark to space ratio - that's the phrase I was after, rather than PWM of course.

I'm with you both - I may need to build something and try it.

thanks anyway