What is a suitable input for VSS from Toyota 3 Wire?

[Danbob]

I've tried searching for this but can't find a thread which shows a successful end result.

My car has a 3 wire Gear driven Toyota Speed sensor (MR2) - I believe it's a 12V pulse.
I have a MS3 with MS3X card.

Can I take the signal directly from the sensor to the Megasquirt?
Which input is suitable?
I don't know if it's a 12V ground pulse or 12V live pulse, do I need to know that to know which input I need to use?



Thanks again,
Dan

[billr]

First, figure out if it is a grounding output or "live". That will determine whether you need a pull-up resistor. If you do, then pulling-up to 5V would be safest, but I think there should be little/no problem using a "live" 12V signal. Do you know how many pulses-per-mile the VSS outputs?

[Danbob]

Only info I have so far is this:


The 3 wire speed sensor output signal is a square wave signal that connects between the input power source (battery voltage) and the power ground. The speed sensor normally outputs 4 pulses (High to Low voltage transitions) for each speed sensor revolution.

Seems majority of 90's Toyota's used this type of sensor so hopefully somebody will have used this sensor with megasquirt before

[Danbob]

I'm struggling to find any reliable information on the sensor output.

The main thing for me to understand is, once I know if the pulse is a 12v grounding pulse or a 12v live pulse, does it mean that if it's a ground pulse I should use datalog in as it's set up for ground, and if it's a live pulse I have to use N2O in as it's the only live input?

Can somebody help me with that aspect?

[Danbob]

OK I now know the sensor output.

Output wire will see 0V and pulse to almost 12V four times per revolution.

As it is a positive pulse, do I need to wire this to the N2O input? As it is the only input setup for a positive voltage?
Or should I wire it to a ground input (datalog in?) and it will detect the inverse of the positive pulse as it may not consistently reach 12V at each pulse?

Can somebody help? I don't know enough about the way the inputs work to know what I'm doing with this, I don't want to have to open up this harness and change pins once it's all done.

Thanks
Dan

[billr]

If the VSS is actively pulling to ground, and it probably is, then using the "datalog" should work. There is already a pull-up to 12V for that input and the VSS would just have to ground its internal pull-up along with the input's built-in pull-up.

[Danbob]

Thanks for the response.

How can I test/be sure that the vss is "actively pulling to ground"?

My electrical background is limited so could you explain why using a ground input in is more appropriate than using a +12v input in this case?

Thanks
Dan

[billr]

Bench test the VSS sensor by connecting it to power and ground, and connecting a 2200 ohm (approximately) resistor between the sensor signal wire and 12V. The read voltage between the signal wire and ground. If it pulses nicely from about 0 to 12V it will work.

Why use the "grounding" input? You have more of them, save the other one for something else. They are really all the same, but that "12V" one has a pull-up that can easily be used or removed.

[suberimakuri]

On a Toyota AE86 we are using Datalog In on MS3X with W57? digital speedo drive.
We are feeding it 5v TPS VREF instead of 12V and it seems fine.
Haven't had any issues with noise or anything, bloody great.

[Danbob]

Interesting, I'll try and find out if it's the same sensor. Does the AE86 have a cable drive to the meter and a sensor to the ECU?

Why did you decide to give it a 5v feed rather than 12v out of interest?

Thanks
Dan

[suberimakuri]

Hi Dan,

Sorry didn't see reply.

Gearbox: We replaced the cable drive output mechanism on the gearbox with a digital 3 pin output off a different toyota - I think a bigger car like Cressida or something. Not running factory gearbox but larger W57 box.
I thought we ran 5v TPS VREF to this digital speedo output, I could be mistaken. Can't check until the weekend or next see car. I think I treated it like a TPS or other ADC type sensor...
MS reads the right speed.

Temporary Aftermarket Speedo: We used one of the MS3X spare injector outputs to drive an aftermarket speedo. Calibrate it and MS in Tunerstudio and it reads fine. The aftermarket speedo takes the usual 12v, ground, signal, illumination.

AE86 Dash:
AE86 factory has cable drive from gearbox right into the back of the dash speedo.
ECU and >105km/hr ringer gets a speed output from dash.

The digital dash AE86 however has a cable->digital converter in the dash that then feeds the digital speedo in the dash. Analog AE86 dash's don't have this digital converter.
We plan to connect the MS to the digital dash, bypassing the cable->digital converter. It takes 3 wires and they are; 12 or 5v?, ground, signal. I need to put voltmeter on it to confirm voltage as forgotten, but confirmed ground and signal.
This isn't my car but the next time get to work on it will do this and also connect up some other sensors (fuel/oil pres/temps).

By having everything go via the MS we can calibrate both input and output.

[Danbob]

Thanks for the detailed response.

I've since done a lot of investigation on the car and found the following....

The sensor (mk2 mr2) is fed 12v and the output is pulled both high and low on a square wave pattern. 12v-> Ground ->12v -> ground. However at the oem ECU pin you see 5v -> ground -> 5v -> ground.

This is because on the mr2 the sensor feeds the dash directly, but not the ECU pin. The dash takes the 12v -> ground signal from the sensor and outputs a new 5v->ground square wave which goes to the ECU aswell as the power steering ECU.

So to conclude my own question, as this secondary signal actively pulls to ground, I have used a ground input (datalog in) the same as you, and although not plugged in yet, I'm confident that it'll work

Cheers.
Dan

[dontz125]

The Datalog pin on the 3X card has a 12v pull-up, so you should be good to go.

[suberimakuri]

Hi Dan,

You're welcome, your info is great. Looks like it will be sweet.
Your info leads me to think the AE86 digital dash speedo will take a 12v feed plus signal from MS, plus ground.

Good luck.