Having trouble getting VR sensor RPM signal

[UBSAE]

We are running a megasquirt V3 board. We have it wired for a VR sensor. We are able to get an RPM signal when changing the crank wheel teeth to zero while using the stimulator and adjusting the trim pots. When we attach the ECU to the car, set the teeth to 60, with 2 missing, we are unable to get an RPM signal during cranking. At this point we are stumped to whether it is a software or hardware issue.

Does anyone know of any issues of converting the analog crank signals to digital for the megasquirt to read? The stimulator supplies a digital signal for RPMs and it works fine. We've attempted inputting a AC signal using a function generator, but we are unsure if the comparator circuit for the VR-IN functions properly under the AC signal.

Our old MC34072AP IC for the comparator circuit, while the LM2904N. They are both V3, and seems to be one of the only different components I can see. Could this be causing our problem?

Anyone with any ideas or knowledge, your help would be greatly appreciated. We need to get this engine running!

Thanks,

Andy Walker
UBSAE

[grippo]

You can look at the rpm gauge and see if it moves. You can also run a datalog and look at thr trogger+/- column and see what it is doing. It stays at 0 if it is getting consistent times between teeth, it counts up if getting extra noise pulses and counts down if missingg pulses. But the best of all is to scope the VR input, the VBROUT which goes to the processor, and the signal from cpu to the coil driver.

[UBSAE]

You can look at the rpm gauge and see if it moves. You can also run a datalog and look at thr trogger+/- column and see what it is doing. It stays at 0 if it is getting consistent times between teeth, it counts up if getting extra noise pulses and counts down if missingg pulses. But the best of all is to scope the VR input, the VBROUT which goes to the processor, and the signal from cpu to the coil driver.

Well we don't have an RPM signal for sure, I don't even have to look at the gauge to tell because we aren't getting spark or fuel. I'm going to try datalogging later and see if it shows me anything I don't already know.

I've scoped the VR input on the board, and I've got a cranking pulse. I've traced it through the board, and I think my problem is at the U7 chip I mentioned in my first post. It doesn't seem to be converting the signal from the sensor to a digital signal properly. The ECU is going to be played with a little later on today and I'm going to see if any progress can be made.

Anyone else have suggestions?

[Heribert]

Hi,
If you are the happy owner of a signal generator you can quite simply apply a sinus , triangle or square wave AC voltage of a few volts amplitude
to the VR input . This shall be amplified and converted to a phase-true square wave that is then routed on to the µPC.
It will not give you any rpm reading since there is no missing tooth, it is quite simply a test signal to check the function of the VR input circuits.
Scope your way thru, and you will no doubt find out.

And even without a signal generator, you can still test.

If you have a transformer with a secondary of 5-10 Volts at mains frequency you can use that.

One place to find one is by cannibalizing an old style Wall Wart, the variety with a small mains transformer , taking down the mains to some 5-10 Volts.
Connect directly to the secondary AC voltage , dump the rectifier/filter cap stuff in it.
AND DO BE CAREFUL, the primary side is on mains potential and as such a real danger.

Good luck.

Heribert

[UBSAE]

We actually hooked it up to a function generator in my circuits lab on Thursday. No luck. The VR circuit was outputting a a nice square wave with a frequency about 60Hz, but as we increased the frequency and amplitude, the signal remained the same size, but just became noisy.

We are questioning the health of our sensor at this point, and we may end up switching to another with thats got an AC>DC converter built into the sensor itself.

I'm going to do some more testing and see what I can do this weekend. I may try and build the crank wheel simulator that I saw on the mega-manual site, but I don't know if that will get me any farther than the function generator.

I can't believe that we are still having this issue when we've already had RPM, spark, and injection magically appear and disappear a couple of times. I am also going to be rebuilding ground and 12V distribution blocks tomorrow, maybe this will make a difference?

Anyone else?

Thanks for everyone's input thus far.

[UBSAE]

bump....anyone?

[grippo]

If you are getting no rpm during cranking you can check for the problem by scoping the output of the VR circuit that goes direct to the processor. If this is a clean 60 - 2 tooth signal on the scope then you may have a configuration problem, so you can post your msq. But you indicate it is not a clean signal and that it appears to be a problem with the U7 chip. If the output of that goes to the processor VR in and the input to U7 is correct, then that is the problem and you need to get another U7 chip. You can also use the TachRef program to see what your cranking signal looks like TO THE PROCESSOR. If this is a clean 60-2 signal then your msq is likely wrong.