EUDM gauge cluster

[banpei]

Some fruits of my work:

On the left the JDM speedometer and on the right the EUDM speedometer. You can see the biggest difference at the bottom where the chime gets its signal from. The mechanics work quite simple: the copper contact runs over a lobe (also present on the EUDM) and this makes contact with a small "drum" that's attached to the speedo needle where it can only make contact when exceeding 100km/h. This explains why the frequency of the chime increases when you drive faster. I really need to make a video about this to explain it in detail. As you can see, the EUDM speedometer lacks the chime function and the drum completely.

Even though both are specified 637 revs per km/h, their scale is clearly different. The Japanese starts with 0km/h at 8 o'clock and reaches 100km/h at 12 o'clock. The European starts with 0km/h at 9:15 and reaches 100km/h at 11:30. This means you can't just swap over the Japanese speedometer into the European gauge cluster as then the scale would be off. You would be able to swap over the "electronics" and the drum, but then it would start chiming at 110km/h.
Another reason why it wouldn't work is because my EUDM cluster is LHD and the JDM cluster is RHD. Because of this the reset stalk of the trip meter is on the other side and this makes it incompatible as well.

The speedometer has either two (EUDM) or three bolts (JDM) that made contact with the sheet with the circuit on it.

The top bolt (I'll call it terminal #1) is the chime switch and this is missing from the EUDM cluster. The middle bolt (terminal #2) is connected to ground. The lower bolt (terminal #3) is sending the speed signal (4 pulses per revolution).
The lobe is basically pushing a copper rod up and down. This rod then touches the drum that is attached to the needle. This then closes the circuit between terminals #1 and #2, and this allows the chime to go on and off. I'm not sure if terminal #1 is also connected to another relay to operate the chime, but I don't think it would be necessary for the operation.

In the service manual is states terminal #3 of the speedometer sends a speed signal to the ECU and this terminal is called "EFI Computer". This is the infamous speed signal used in the ECU to revlimit the engine when unstressed (e.g. not moving a car), which is 6500rpm for a bigport. I was hoping this speed signal would be either a pulse or a resistance. If this would be the case, I could have hooked up an arduino board, interpret the signal and then use that to "fake" the speed chime. Unfortunately, my multimeter doesn't seem to be able to pick up this signal. Maybe it's just averaging out whatever it reads and therefore it always outputs a similar reading. So that's too much hassle to implement for now as I'll first have to program the arduino board to catch the pulses. Maybe somewhere in the future I'll invest more time in this, but for now I'm done with this.

I'll make some footage in the (near) future and post the video of the inner workings. In the meanwhile, if you have any (specific) questions I can still have a look at it and answer them when necessary.