EUDM gauge cluster

[Uzelac]

(02-13-2018 09:49 PM)Project D Wrote:  Just wanted to provide the correct information on this.
The 2 connections on the speedometer are not there for the needle (who work purely on the eddy current principle*) but are connected to a reed switch to give you speed signal to the ECU.

This is correct, i use cable and reed switch with aftermarket ECU as speed sensor.
Works just fine.

[banpei]

Still looking for one...

[Power_uP]

Would a UK AE82 GT cluster be adequate? I have one that is missing the temp gauge, but is otherwise complete.

[Ivan141]

I have one or two, one is in bits. What are you looking to find out?

[banpei]

Two things: one is that I want to perform a teardown and compare JDM with EUDM. Next to that I have an idea to put an arduino board in there and try to mimic the chime. But given my excellent skills I'll probably blow up the board on the first try.

[Ivan141]

(09-15-2021 08:38 PM)banpei Wrote:  Two things: one is that I want to perform a teardown and compare JDM with EUDM. Next to that I have an idea to put an arduino board in there and try to mimic the chime. But given my excellent skills I'll probably blow up the board on the first try.

It's quite simple on the EUDM version: the tachometer has it's own board with some logic to drive the needle, there is a simple little pcb for the econ/pwr light, and the speedometer is fully mechanical (eddy current drive).
The difference is likely to be in the speedometer, it would be interesting to know if you can connect a chime to the EUDM one, but I dont think you could duplicate it with an arduino easily since you would need a sensor on the speedo, which is not easy to do.

[banpei]

I don't expect it to be very different from the JDM version. As I could find a teardown of the USDM and AUDM gauge clusters, but not for the EUDM. So the teardown is meant for documentation purposes.

According to the documentation I found on AUDM and JDM speedometers and Project D's reply it should give a pulse output. For JDM ECUs it won't allow you to rev beyond 7000rpm unless there is a signal in the ECU coming from the speedometer. Probably they did this to protect the unloaded engine. According to the wiring diagram in the AE86 workbook the LHD gauge cluster should also output a signal to the ECU, so that's why I'm hopeful I can tap into the pulse signals and count them with an arduino and then send out a signal on another channel.
(probably it still involves a relay to send power to the chime)

[Ivan141]

This is all there is to the speedo. I would be amazed if it puts out pulses as it looks 100% mechanical.
[smalle edit] 2 of the screws are connected to the pcb, it might have some switch in there yet, would need to hook up
a drill to find out.

[banpei]

Thanks for the photo Ivan!
It looks like it's the exact same as on the JDM cluster:

The top pin is connected to pin 7 on the connector, which is marked as ECU / Speedo signal in the JDM diagram. That means the speedo is probably the exact same part and only the fascia is different.
I can test my JDM speedo later this week and see if it sends any pulses on that pin.

[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.