9 replies to this topic

[vxmagpie]

I am toying with changing my instrument cluster to a race technology dash 2. My question is to do with the speedo signal. I know that the signal is generated by the abs wheel sensor and the abs ecu. Is the signal converted before it reaches the instruments? Or does the speedo accept the signal as it is? I haven't taken the dash off so I don't know if there is some sort of pulse converter/box fitted in line from the abs to the speedo. If not I will have to fit a secondary Hall effect sensor to the front hub. Any help will be much appreciated.

[ciderbooze]

I may be completely wrong here but I thought it was PWM

[vxmagpie]

I think a PWM signal is a sine wave form. The Dash 2 has no way of converting this and only understands a Hall effect signal. You can buy a converter to go inline but then you'd have to know how many pulses etc/teeth on the abs signal.

[techieboy]

As I understood it, the ABS ECU converts the raw ABS sensor speed signal to a square wave signal and supplies this to the dash and main ECU. Sure it's been talked about a few times on here, so probably worth having a search. There's certainly a couple of cars that have had Race Technology Dash's fitted to them, in the past.

[Arno]

I am toying with changing my instrument cluster to a race technology dash 2. My question is to do with the speedo signal. I know that the signal is generated by the abs wheel sensor and the abs ecu. Is the signal converted before it reaches the instruments?

 

The ABS ECU gets the low voltage sine-wave signals from the hubs. It uses the rear right one to generate a simple 5V pulse signal which is fed to the ECU and the dash.

 

So on your DASH2 you'd either need to use some sort of 'high voltage' input for the speed sensor or add a new one to one of the wheels and connect it directly to the dash.

 

Generally you do not want to tap into the existing hub wires for this as the signal is quite weak and gets distorted easily which gives the ABS system the wobbles..

 

Bye, Arno.

[vxmagpie]

So is the speedo signal a Hall effect signal? And if so how many pulses? It might be easier just to add a new Hall effect sensor to a front wheel. Thanks for everyone's help, it's much appreciated.

[Arno]

AFAIK are the original ABS speed pulse rings inductive pickups, not hall sensor based.

 

If the DASH2 can only work with a hall pickup then the best course of action will probably be to fit a sender and pulse ring on either a hub or a driveshaft/CV joint.

 

Bye, Arno.

[ciderbooze]

A Hall effect sensor (maybe ) is used to generate the sine wave the abs ecu cleans it up into a square wave and passes it along to the stack. I thought the square wave produced was PWM to indicate speed but others have said it's just a straight frequency conversion. I don't know what you are planning to fit but you will need to find out what type of input it wants then either convert what you get from the abs ecu or fit your own independant speed pick with the correct output suitable for your new dash. Edit : so not Hall effect at all

Edited by ciderbooze, 26 April 2014 - 05:11 PM.

[vxmagpie]

The Race Technology Dash 2 will only accept a clean square wave signal from a Hall Effect Sensor. There are lots of aftermarket converters that allow you to use existing sensors on the car, but you need to know the exact type of signal and how many pulses per wheel revolution. I have not been able to find a conclusive answer to any of these questions. Buying a Hall effect sensor is not difficult, but mounting it will pose a few challenges. It would be easier to use the existing signal, but for it to work correctly the Dash 2 has to be programmed correctly with pulses per mile to calculate wheel speed. Thanks for your help.

[Dave H]

I have spent days messing around with the ABS signals in order to obtain a clean signal suitable to enable me to get the Traction Control working on the Adaptronic 440 ecu.

 

The signals from the hubs are sine waves with a small amplitude at low speed which increases with speed as does the frequency. Each wheel sensor feeds the ABS controller with a twisted pair of wires. The rear left sensor is used for the speedo signal. The output from the ABS unit is a square wave. (I can connect the oscilloscope next week and let you know the amplitude if you like? From memory this is pin 3 on the ABS unit and again I can confirm this when back at the workshop)..

 

The big problem I've had is noise on the signals. You can't earth either of the wires between the sensors and ABS unit as it brings up the ABS light. The first simple circuit I built works fine over about 6 mph but below this the noise was causing the Adaptronic ecu to show about Mach 2 !!!!! Several circuits later and I think I've just about cracked it obtaining a good clean square wave as soon as any rotation of the wheels occurs. 

 

Dave.