964 speedo signal from ABS sensor

[924ttturbo]

Then 964 speedo signal comes from the front left ABS sensor and is converted into a speed signal.

Is the signal converted just by the ''control unit frequency converter'' (964.618.220.00) or also by the ''abs control unit'' ?

[lucittm]

On the 1991 model the signal comes in from the ABS unit as fed from the LF wheel sensor. It goes to R52, the Frequency Control Unit and also to R24 if you have a Carrera 4, then to the speedometer. The purpose of the FCU is to produce a square wave output using a device such as an ITT UAF 2115. The output of this integrated circuit is used to clean up the pulses from the ABS sensor.

To help with the translation of your FCU in the picture: Pin 2 is Terminal 15 (+12V) via Fuse 18, Pin 5 is "Output", Pin 6 is "Input", and Pin 7 is Terminal 31 (Ground).

Does that help?
Mark

[924ttturbo]

I don't have the ABS system anymore, just the hubs and sensor. Can I make the speedo work like this:

[lucittm]

I think you can try, it can't hurt. My 1991 schematic shows four wires leading to the speedometer as follows:
Orange to pin 1, this is +12V with the key on (Terminal 15)
White/Red to pin 2, this is the speedometer output for the OBC, convertible top, spoiler, etc.
Brown to pin 3, this is ground.
Green to pin 4, this is the input signal from the FCU pin 5.

The other connector on the ABS sensor is a shield and it is tied to ground in the ABS Control Unit.

Good Luck,
Mark

[924ttturbo]

Problem is, that there is no diagram of the inside of the 'ABS control unit', so I don't know if the signal is putted straight to the relay.

[javaschlava]

Hey 924 turbo,

Did you ever get your speedo signal to work the speedo without going through the ABS unit, wiring it like you posted? Just through the fcu relay?
Any other good posts on this?

[scootermcrad]

I hate to bump this up, but did this work? Has anyone else tried this? Anyone with a '91+ G64, specifically? I'm looking for information on this topic, as well. Thanks!

[mysocal911]

Originally Posted by scootermcrad

I hate to bump this up, but did this work? Has anyone else tried this? Anyone with a '91+ G64, specifically? I'm looking for information on this topic, as well. Thanks!

The ABS sensor only provides a low level signal, less than five volts. The ABS ECU provides a signal that goes to about 12V, which speedo needs.

[scootermcrad]

Originally Posted by mysocal911

The ABS sensor only provides a low level signal, less than five volts. The ABS ECU provides a signal that goes to about 12V, which speedo needs.

So the FCU module cannot be wired as mentioned above in the diagram provided by @924ttturbo to provide the signal needed for the speedometer? It actually does have another translation within the ABS unit of some kind?

I'm looking for a way to run a 964 speedometer without the ABS unit, similar to what others have mentioned. I'm wondering if I'm going to have to look at building an Arduino setup of some kind to simulate that signal.

[mysocal911]

Originally Posted by scootermcrad

So the FCU module cannot be wired as mentioned above in the diagram provided by @924ttturbo to provide the signal needed for the speedometer? It actually does have another translation within the ABS unit of some kind?

I'm looking for a way to run a 964 speedometer without the ABS unit, similar to what others have mentioned. I'm wondering if I'm going to have to look at building an Arduino setup of some kind to simulate that signal.

The ABS sensor signal needs to be amplified, and then sent to the frequency conversion 964 module/relay (FCU), and then to the speedo.
The complete conversion (amplification/square-wave) can be done within the FCU.

[scootermcrad]

Originally Posted by mysocal911

The ABS sensor signal needs to be amplified, and then sent to the frequency conversion 964 module/relay (FCU), and then to the speedo.
The complete conversion (amplification/square-wave) can be done within the FCU.

Thanks for the response! So, to clarify what you're saying, that initial signal coming from the wheel sensor (assuming a square wave, also) is processed by "something" in the ABS control box before the signal is amplified by the FCU on its way to the speedometer. So the ABS control box DOES serve some purpose and the FCU isn't doing all the real work.

I've been trying to figure out if I can bypass this box, as suggested early on in this thread, and rewire using only the FCU to relay the speed signal to the speedometer.

Sounds like I may need to create an Arduino setup to accomplish this. I may be able to set this up to amplify without the FCU, as well. Would be nice if it could all happen in one nice, neat, little "black box". Signal in. Signal out.

[mysocal911]

Originally Posted by scootermcrad

Thanks for the response! So, to clarify what you're saying, that initial signal coming from the wheel sensor (assuming a square wave, also) is processed by "something" in the ABS control box before the signal is amplified by the FCU on its way to the speedometer. So the ABS control box DOES serve some purpose and the FCU isn't doing all the real work.

1. sine wave @ wheel - about 1-2 Vrms
2. ABS provides 12V square wave

Originally Posted by scootermcrad

I've been trying to figure out if I can bypass this box, as suggested early on in this thread, and rewire using only the FCU to relay the speed signal to the speedometer.

Sounds like I may need to create an Arduino setup to accomplish this. I may be able to set this up to amplify without the FCU, as well. Would be nice if it could all happen in one nice, neat, little "black box". Signal in. Signal out.

All signal processing from sensor can be done in the FCV.

[Raceboy]

One can use simple device based on LM1815 to convert sine wave to sqaure pulse signal:
https://shop.vems.hu/catalog/product_info.php?products_id=162&ceid=2bab37472adbd935ff15b1a00b2acea6

[scootermcrad]

Originally Posted by Raceboy

One can use simple device based on LM1815 to convert sine wave to sqaure pulse signal:
https://shop.vems.hu/catalog/product_info.php?products_id=162&ceid=2bab37472adbd935ff15b1a00b2acea6

That looks pretty simple, indeed. Thank you for sharing that!

Has anyone tried the VEMS components for this application? Certainly seems it was just about made for this sort of application.

Also, thanks to @mysocal911 for some messaging regarding this topic.

This discussion has certainly proved I am NOT an electrical guru!

[mysocal911]

Originally Posted by Raceboy

One can use simple device based on LM1815 to convert sine wave to sqaure pulse signal:
https://shop.vems.hu/catalog/product_info.php?products_id=162&ceid=2bab37472adbd935ff15b1a00b2acea6

From the link; "Requires 5V supply (from the assembled v3 controller EC36/28 pin, or other source, only appr. 10mA needed)."