Stock cluster VSS signal parameters

[citizen_insane]

I don't recall what the voltage is, but the 'nitrous in' pin will work fine with the VSS output from the cluster.

Awesome, thanks for the confirmation!

The reed switch in the diff grounds the line, which is pulled up to Vbatt normally.

The cluster simply acts as a buffer as far as I can tell. It is a ~11.5V square wave pulled to ground as a vane passes the red switch.

100% I plan to use the cluster to process the signal since I'm still running it (my secondary tablet dash will be mounted to the dashboard center console).

Based on this statement, I think the "Nitrous In" input is the correct one to use since it'll be providing voltage to the pins on the MS3X.

Jaxx, you're right on the money with the VSS/RPM gear calculations. My plan is to run a blend table for boost by gear to maximize traction.

[nando]

It goes through a processor that's specifically designed for VSS signals. I have the datasheet somewhere, if I could remember what it was called.. lol.

[bmwman91]

The reed switch in the diff grounds the line, which is pulled up to Vbatt normally.

The cluster simply acts as a buffer as far as I can tell. It is a ~11.5V square wave pulled to ground as a vane passes the red switch.

[nando]

It's not though. Otherwise there would be no point in the cluster pre-processing it. It might be good enough to use for MS, but if you still have a cluster, the built in VSS wire makes a lot more sense.

[Jaxx_]

Don't attach the reed switch directly to Megasquirt. Let the cluster process it first. Just tap into the cruise control VSS output, which is right in that picture (C6). it's a black/white stripe wire. Actually, the stock engine harness likely already has a VSS wire, which you can also use.

I don't think it's necessary, but ok. I don't have a cluster anymore

edit: this is to say that I believe it is already a square wave from the diff--but I don't have a scope

[nando]

Don't attach the reed switch directly to Megasquirt. Let the cluster process it first. Just tap into the cruise control VSS output, which is right in that picture (C6). it's a black/white stripe wire. Actually, the stock engine harness likely already has a VSS wire, which you can also use.

[Jaxx_]

Yes, it's a ground switching circuit. For my '84 I used the attached diagram. It might be different for other model years.

Connect C2 Pin 12 (Brown/Red) to Megasquirt ground switch input. I used Launch In myself.

Connect C2 Pin 8 (Brown/Violet) to Ground.

Here are my other settings:
VSS1 Input Type: Digital
VSS Position: Wheel
Speed Sensor Teeth: 9

VSS Dot smoothing:
Sample Interval(ms): 200
Lag factor: 50
VSS Sampling Interval(ms): 50


You can also setup gear detection as VSS/RPM, as I'm sure you know. I use my "6th" ratio as reverse.

[nando]

I don't recall what the voltage is, but the 'nitrous in' pin will work fine with the VSS output from the cluster.

[citizen_insane]

I tried searching here and on msextra to figure out what signal is sent from the stock E30 cluster to the ECU, but I'm not finding much and it's kind of hard to test since it requires the vehicle to be moving.

As I understand it, the sensor in the diff is a reed switch which sends a signal to the cluster, which is then conditioned into a square wave pulse with 9 pulses/wheel rev.

My issue is understanding what this "pulse" from the cluster actually is. Is it a switch to ground? Is it a 5 or 12V signal? This matters because it determines which input on the Megasquirt I wire to the signal. The MS3X "Launch In" supports ground switching inputs and the "Nitrous In" supports +12V switching, both are selectable as options in the VSS menu.