Road Speed and Engine Speed signals for HUD

[Gray S.]

Hey everyone,

One of my buddies is going to try and program a heads up display for his senior design project (computer engineering major) using my e30 as the test car.  For the HUD we are thinking he needs to tap into 2 different wires.  One that gives the road speed (mph) and one that gives engine speed (rpm).  
The HUD unit will be located on the dashboard right behind the cluster bump and close to the windshield.  Without tearing into the ECU, are there any wires running to the cluster or otherwise easily accessible that we could tap into?  

Is it possible to get those signals directly off the cluster itself?  We are just in the planning stages right now and want to figure out the easiest way to get these two signals.  

Any suggestions would be much appreciated!

Thanks,

Gray

[DesktopDave]

There is a signal wire from the diff that sends speed info.  The DME converts mph IIRC.  Not sure which wires you'd tap, might be rough to find mph if it's a converted signal.

The yellow connector on the gauge cluster has a speedo output for the OBC.  The cruise computer uses a connector marked 'a' off the green clip.  M42's don't have that, but you can grab it off another cluster.  Look up the cruise control install thread.

[Gray S.]

So if the DME converts the signal and then sends it to the cluster, there must be a wire in one of the cluster harnesses/connectors that sends the converted signal to the speedometer itself.  

Where would I find a pin out of what all the wires in the cluster harness connectors do?

[DesktopDave]

You have me curious, at least for fixing my speedo.  Here's a link for repair:
http://www.r3vlimited.com/board/showthread.php?t=95733

Here's a link for modifying the cruise control speed output:
http://www.unofficialbmw.com/speedo/speedo_d.html

I'm sure I'll dig up something else eventually.  Share anything you find.

[Gray S.]

I most definitely will. We will be working on it pretty soon here so hopefully we will find something useful.

[Gray S.]

Very brief update: we took some readings with the Multimeter running a wire to the c101 pin 14 in the engine bay.  From all the research we've been doing it seemed fairly certain that we would get a speed signal here.  There was also supposed to be the engine speed signal located at pin 9.  Interestingly enough, the multimeter picked up a reading at pin 14 that fluctuated exactly in line with the engine speed!

I believe the reading was between 400hz at idle and 12000hz at 7000rpm.  My digits might be off a bit there as my buddy was holding the multimeter and I dont have much electronics background.  The multimeter read .400 at idle and 12.000 at 7000rpm.  

I'm a little unsure what to make of these numbers.  They perfectly mirror a signal that would measure rpm (I would rev the car and the readings would fluctuate accordingly).  But all of the people doing M50/S50 swaps seem to have road speed signal located at that pin.  

We ran out of time tonight but are going to spend awhile testing different things tomorrow so hopefully I'll have something to report back.  Hopefully we will be making progress!

[Gray S.]

Went home and tested some more yesterday with no sucess.  It seems like al the information about location of speed signals doesn't apply to my 318is.

Going from this wesbite http://www.unofficialbmw.com/speedo/speedo_d.html I soldered a test wire to my speedo just like in the picture, and nothing.  No signal at all.

Since we couldn't get that to work we tried looking under the glovebox for this connector.  The black wire should contain the rpm signal.


Unfortunately I couldn't see that connector anywhere in my car.  I took off the plastic ECU cover and still couldn't find it.  So I'm not sure if its buried somewhere else back there or if my car doesn't have it at all.

We also looked at the yellow OBC connector on the back of the cluster for the road speed signal.  Supposedly theres a wire that sends that signal from the cluster to the OBC.  I just am unsure if my car would even have it considering I only have a 6 button OBC.  I was also not able to locate a pinout chart for that yellow OBC connector.

Also, how would I go about testing the pins on that connector?  Doesn't the connector have to be plugged into the cluster to get the signal?  Would I have to cut and splice every wire running to that connector?

So far this has been frustrating.  I've done a huge amount of research but there are no definitive answers.  I was hoping these two signals would be fairly easy to get without having to tear into the car, but its looking less and less promising.  

Any tips or help would be extremely appreciated!