80s OE sensors with Motec M150

Hi all,

I'd like to retain some of the original sensors on my EFI/ITB converted 1983 Ferrari 512 BBi. One of which is the original vehicle speed sensor that feeds the speedometer (pic attached). Are there any suggestions on how to get this OE sensor to work with the M150? Ideally, I'd split the signal to the dash and the ECU. However, I wouldn't be opposed to sending solely to the ECU, then sending a new calibrated signal to the dash from the ECU.

Thanks in advance,

Robert

If it's a 2 wire sensor used for speed sensing then I would guess it's just a variable reluctor sensor.

If that is the case you should be able to wire it to UDIG input and sensor 0v.

The polarity will just define the signal waveform whether it rises or falls as the tooth passes.

Oh, good point. I actually use a UDIG with the OE distributor reluctance sensor. I'll try that.

What about something like an old oil pressure or oil temp sensor? Would AV and/or AT inputs work for those?

Tentatively yes, there most likely will not be a calibration for them so you would need to have that done. Some of the older single wire sensors are not recommended for use as they are very inconsistent in their behavior as they rely on the engine grounds to complete the circuit back to the ECU, so they can get noise and other errors induced from this.

Hey guys,

Getting back to this after taking a break to work on other projects. The factory wiring for this sensor is 12v from the fuse box, with the other wire going straight to the speedometer / odometer. So I'm guessing the UDIG/0V option above isn't going to work. Any thoughts? Maybe a Half Bridge for the 12v and a UDIG for the "signal"?

If I had to guess it's hall effect the bat +ve powers the internal circuitry, the other wire is the signal to the cluster which would be pulled high and goes low when a tooth goes past and the ground is through the sensor body?

It is a reed switch, it just shorts the two pins together when a magnet goes past the end. Just connect the ecu digital input to the same wire that goes to the speedo. Leave the pull-up in the ecu turned off.

http://www.dinoplex.org/instruments/vegliaspeedosensor/index.html

Here's a good article showing the guts of this sensor. Not hall effect like I guessed.

So Adam would be right splice the output signal into a UDIG.

Thanks for the link, Scott. It looks like this sensor is a VR sensor. I tried connecting to a UDIG, but I am only seeing a steady 3.5V. I am under the impression UDIG requires a digital signal, with the exception being channels 1 and 2 (crank / cam) have built-in conditioning for VR sensors (which I am using).

So that leads me to believe the M150 cannot process this signal without first "conditioning" to a digital signal. Does that make sense? Any suggestions?

That article does not describe a VR sensor (well internally the coil is), but it has additional circuitry that makes it a current-loop sensor -- 1-2 mA without a target detected, and 10mA with a target detected. So you could connect the signal side of the sensor to a resistor (and the other end of the resistor to ground), then you would measure a voltage change as the target is detected. A 560 ohm resistor to ground, would produce 5.6V (V= I x R or 0.01 x 560) high, and about .84V (0.0015 x 560) when low. The article pics shows something like that.

Consider trying a resistor to ground and see what the voltage does as you pass a target.

BTW - The M150 Universal Digital Inputs can handle a variety of digital signals, with programmable threshold and pullup resistor control.

All of the available UDig sensors in an M150 are capable of using VR sensors if they are wired correctly. There is no difference between the UDig inputs.

Reading the information provided by Scott, the sensor may have a fault if the voltage doesn't change from 3.5V when tested.

Okay, thanks David. I'll try that. Somewhat rudimentary question here, but can you recommend a good way to get 12v from the ECU to the sensor? I have a PDM, and I can splice off the ECU 12v supply, but can I simply enable a half bridge (or something similar) to send 12v on an output pin? Eg, an "aux output"?

Maybe answering my own question here, but curious your thoughts. I got this working by adding a resistor (to ground) on the UDIG, as well as enabling a half bridge on an aux output. The aux output is set to -100% duty cycle, with a 0 frequency – which I believe basically makes it behave like a 12v switch (no PWM).

I set the wheel speed ratio to 1, then drove the car while watching the GPS and gradually increased the teeth count until the speed matched the GPS (after making sure the wheel dimensions were correct, etc.). Voltage varies between ~0 (no target) to ~8 (target), so I set the threshold to 4 and tweaked the hysteresis, etc..

At this point, it's working and I'm within 1 MPH of the GPS.

Anything you all suggest for improvements?