Driveshaft RPM Sensor

[Hando7]

I have a Hall Effect driveshaft rpm sensor which outputs a voltage pulse every time the magnet on the driveshaft passes by the sensor. I want to add the sensor to my Pro Link cable to log driveshaft rpm and then setup a math parameter to compare engine rpm with driveshaft rpm with trans gearing factored in to calculate slip. The issue I am running into however is that I do not see a way to transform a pulse signal coming in to rpm.

I was thinking if there was a way to continuously add all the pulses to a running total, I could set up a math parameter to calculate as shown below where SumPulse is the running total.
(SumPulse-Shift(ms)SumPulse)/(ms*2pulse/rev) * 100ms/1s * 60s/1min = RPM
Is there a function to register a pulse as a single count and sum it to a running total to input into this math parameter?

If anyone else has any methods they've used to set up a Hall Effect sensor for rpm data logging in HPT I'd love to hear how!
I may just be overthinking this, but haven't been able to find any info online.

[TheMechanic]

With zero information on vehicle, no tune file etc. etc. it difficult if not impossible to help you. All I can say is most modern transmission have an output speed sensor on them already.

[blindsquirrel]

It would probably be easier all around to wire it to the ECM/PCM/whatever you're working on and log it as if it were the original VSS.

[Hando7]

Sorry, didn't realize vehicle info was important since I am just trying to data log through VCM scanner using the HPT pro link cable.
Vehicle is a 1998 Camaro (V8, Auto Trans) with a 2002 Camaro PCM. Trans was swapped from a 4l60e to a TH400.

Interesting idea using an existing PCM channel with the driveshaft rpm sensor.
Unfortunately the VSS sensor only run to the ABS module on these vehicles for traction control and not the PCM. There are no links to the PCM and thus no way to data log from what I can tell.
I don't think there are any other PCM channels on the vehicle that take a square wave form, even the speedo input (which I still need for the speedometer) takes an AC sine waveform.

[blindsquirrel]

Unfortunately the VSS sensor only run to the ABS module on these vehicles for traction control and not the PCM.

So the factory diagrams are wrong, and there's really nothing going to PCM C1 20/21?

2002 M6.png 2002 A4.png

Now, I don't know if the PCM can be set up to read 1 pulse/rev, but if you're using a 2002 PCM and it's pinned for a 2002 OS, then there is a place for a VSS input.

[Hando7]

I guess I misspoke before I was referring to wheel speed sensor when I said VSS.
The VSS input you are referring to are for the speedo. As I said before, this is an AC signal, not a square wave form so it will not work. I know this for a fact because I had to run a square to AC convertor to make my speedometer work again after the TH400 swap. I also still need this for my speedometer data and gauge.

[TheMechanic]

Those pins you are referring to are for the speedometer from the transmission output.
This input is an AC signal, not a square wave form so it will not work. I also still need this for my speedometer data and gauge.

No. These are used for transmission shifting etc. They do not go directly to the cluster through a buffer etc. This is not a pre OBD2 vehicle. It is necessary for a PCM/ECM to have a transmission output speed sensor to calculate emissions functions also.

[blindsquirrel]

You already have a sine/VR-type signal coming from the transmission for the speedo? And this signal can't also go to C1 20/21 because...?

[Hando7]

Yes, this VSS signal is hooked up to the PCM....It runs to PCM then PCM outputs to speedo and uses it for other information as you were saying.

Back to my original question however I am trying to log a driveshaft rpm sensor. This is an aftermarket sensor on the yoke of my rear end. I can't hook it up to the PCM pins for the VSS because VSS pins are already being used for VSS.

I have been using the VSS to log convertor slip so far, but I do not believe it is a very accurate calculation given it is not as direct. Tire diameter and gearing need to be taken into account to calculate. Tire diameter does not stay consistent during 1/4mile pass.
I should also note that because I am running the VSS through a square to AC convertor I actually have no idea how many pulses it outputs going into the PCM. So to log trans output rpm directly through this would not be super accurate either. This is why I am using my known accurate VSS signal to back calculate rpm through tire and gearing.