VSS signal from ABS ECU output pins attenuates too much

[Coutsi]

Hello,
I´m reading my VSS1/2 signals from front and rear wheel through ABS ECU output pin (which was used for no removed TRC ECU). My problem is that signal attenuates at higher wheel speeds ~900-1000hz and amplitude decreases too much for MS3Pro to recognize signal (amplitude measured with scope ~1.3V at around 1700hz). Signal rise-time seemed to be quite bad too. How I should fix that problem?

[Matt Cramer]

What pin on the MS3-Pro are you using for input?

[Coutsi]

Digital Frequency 1 and 3 input pins if I remember correctly, my Flexfuel sensor is using 2.

[Matt Cramer]

Does the voltage drop if the ABS unit is not connected to the MS3-Pro?

[Coutsi]

It acts somewhat the same but it needs pullup signal to work without MS3.

[Matt Cramer]

Try adding a 330 ohm pull up to 5 volts in that case. It could be the MS3-Pro's built in pull up is not enough for your ABS controller's output.

[Coutsi]

I tested with 330ohm resistor. Now signal is between 4,96V and 2,48V, steady squarewave through whole frequenzy range so that nice. If I increase resistance, amplitude drops -> 1kOhm + 330Ohm in series signal is between 2,0V and 0,660V. Should I just build comparator in between or is there any other simpler solution?

[Matt Cramer]

I'd just leave the pull up there.

[Coutsi]

Maybe my last message wasn't clear enough.
Using only 330ohm pullup signal isn't sinking enough to trigger on ECU (it should drop below 0.8V).

I can't think of anything else for solution so I'm building comparator circuit which has crossover trigger trimmed to 3.75V.

[Coutsi]

I built comparator circuit and got everything working, now I get VSS signal to atleast 350kmh.