*** MicroSquirt issues with VR Sensor input - fix ***

[RedRocketRally]

I guess I posted too soon. I removed C30 (per the discussion above) and revved right up to 7000 or so before I backed off. It still needs to be tuned, but at least its running.

brian

[A2TURBO]

Ive just purchased my microsquirt and just about have everything wired and ready to install am I going to have to remoce C30? I would also like to know if I can get my tach sig from the - side of my 1/4 coil this an fi only motorcycle (1985 zx900) with an inline four cylinder engine. I only ask because Ive seen posts where people have damaged their microsquirt doing this without the addition of a diode any help would be greatly appreciated!

[Matt Cramer]

You won't remove C30 if triggering off the coil.

It wouldn't hurt to try something like a 10K resistor inline with the coil wire to avoid any damage. Haven't seen many cases of that happening but it's happened once or twice.

[A2TURBO]

Thanks mat Ill let you know how it goes

[Bruce Bowling]

I'm experiencing a problem like this one. I looked at the board of my Microsquirt and it has a surface-mount diode in the spot Bruce circled above, but its a V2 board so I believe it has this fix already.

I've attached an msq and datalog file. I'm losing the ignition signal right around 4500 rpm. I have a VR sensor and a 36-1 trigger wheel. Polarity seems to be correct, but RPM drops out around 4500. I've moved the sensor a bit and gotten the cutout to move to about 5100, but it still cuts out. I am directly driving a Ford-style ACCEL wasted-spark coil pack, like the one pictured at the bottom of the dual spark page of the manual.

Any suggestions?

OK, I *strongly* recommend that you upgrade to the latest code version V2.890, see the post here:

http://www.microsquirt.com/viewtopic.php?f=87&t=23198

I have a F4I engine that was experiencing the exact same RPM dropout at 6000 RPM - setup was a 12-1 tooth wheel. Putting in the series resistor helped this, but I investigated this further.

After a lot of testing, I found the culprit. What was happening was during the missing tooth interval the VR waveform would go to zero, neck up a tiny bit positive, then go negative to complete the pulse. This little "blip" was in the tens of millivolts at idle, nothing to worry about. But the VR voltage is proportional to RPM, so this little blip grows in amplitude.

At 6000 RPM the blip became large enough in amplitude to become a new tooth! Adding in the resistor reduced the amplitude overall, thats why it helps. But then the amplitude during cranking is not enough.

The MSII/uS base code has a rejection that only accepts tach triggers within a band +/- of where the next tooth is supposed to come in. It throws out any outside of this and increments/decrements the Trigger runtime variable. However, there was an error in the missing tooth rejection section of the code which is fixed in this release.

With the new code I am able to rev to 13,000 RPM without any resistor. I am not sure if this will help you or not but for anyone experiencing high RPM dropout I would try the code out - without the resistor. You may be experiencing the "Phantom Tooth" effect, you will know because the Trigger+/- variable will start counting at the RPM region (and above) where the new tooth pops up and stops counting when the RPM is below the magic point.

The code version also fixed the problem while cranking where the engine catches, spins up then dies, and you then have to recycle power to restore the tach signal. People who have experienced this know what I mean....

- Bruce

[The-Dragon]

So if I understand it right, there should be no problem at high rpm’s, if I use two trigger wheels (for ex. 12 and 1 teeth)?
Because I would like to use COP on my bike up to 14500 rpm’s.

[grippo]

The missing tooth isn't the only source of noise. You could also end up with noise on the 1 tooth wheel or on either wheel if you had ignition cables lying near the vr inputs or a bad alternator, etc. But yes, you will reduce the chances of getting an extra false tooth on the main wheel, and if the single tooth wheel caused a problem, you could try a Hall type sensor on it. The other way to reduce noise is to use external ignition drivers to keep that noise away from the ECU board.

[800vtwin]

So for D5 replacement (on ver 1), is it a 1N4148 or can a 1N4004 be used. Should c30 stay or go?

[Peter Florance]

After a lot of testing, I found the culprit. What was happening was during the missing tooth interval the VR waveform would go to zero, neck up a tiny bit positive, then go negative to complete the pulse. This little "blip" was in the tens of millivolts at idle, nothing to worry about. But the VR voltage is proportional to RPM, so this little blip grows in amplitude.

At 6000 RPM the blip became large enough in amplitude to become a new tooth! Adding in the resistor reduced the amplitude overall, thats why it helps. But then the amplitude during cranking is not enough.

- Bruce

Is this related to the freq response of the VR sensor being effected by its load? The VR sensors have an output impedance (not perfect voltage sources) and seem to be effected by their loads.

I recall an exaggerated version of this 'blip' when a 330R resistor was recommend to parallel the inputs of LM1815.

I have to figure out how to bench test this.

[Aaron Silidker]

Curious if you guys think I need these mods.

I plan to directly trigger an LS2 coil on a motorcycle. The LS2 is a well known entity and at this point, I have had enough with trying to use odd components when proven ones exist.

My bike has the potential for high rpm, and I am using a 30-2 trigger wheel. I saw a hundred plus volts in my tests of the stock CDI flywheel VR signal, so I know the sensor has the potential for high voltage. My new trigger wheel has similar tooth height to the stock sensor.

Should I just use a Zener in the VR circuit before the uS or is the diode and cap mod necessary for me?

Thanks guys...keep in mind I am a mech e with little hardware knowledge.