Tach trigger with CDI ignition

[Aaron Silidker]

Yes, I searched, and only found people saying it wouldn't work.

Have a bike that I want to finally get up and running with uS. Want to do fuel only first, so I would like to find a tach trigger to use that works with the CDI ignition that is currently on the bike. Splitting the VR signal from the flywheel is out of the question because the stock signal is 2 pules per rev very close together.

Is there any way I can use the positive voltage trigger signal from the CDI to get a tach signal to the uS?

Thanks!

[dontz125]

Hi, Aaron.

I've thought about this a bit, but it really isn't my area of expertise. What about a REALLY strong (high-volt) Zener diode, 12v output, driving a similarly high-watt-rated opto-isolator? Basically, just beef up the 'normal' coil-in circuit. There may be some polarity issues to ponder, since the normal configuration is to connect the -ve end of the coil (TCI), while you'll be tapping the +ve end (CDI).

The weak of heart (some call them ... wise ) might want to set up a daughter card for the high-zap stuff, with the primary opto-isolator feeding the MS board Hall input circuit...

Good luck!

[supertuner]

What motor are you running?

[Aaron Silidker]

Hi, Aaron.

I've thought about this a bit, but it really isn't my area of expertise. What about a REALLY strong (high-volt) Zener diode, 12v output, driving a similarly high-watt-rated opto-isolator? Basically, just beef up the 'normal' coil-in circuit. There may be some polarity issues to ponder, since the normal configuration is to connect the -ve end of the coil (TCI), while you'll be tapping the +ve end (CDI).

The weak of heart (some call them ... wise ) might want to set up a daughter card for the high-zap stuff, with the primary opto-isolator feeding the MS board Hall input circuit...

Good luck!

Speaking to a mechanical engineer here...you are way over my head here .

[Aaron Silidker]

What motor are you running?

Suzuki DRZ400

[dontz125]

Speaking to a mechanical engineer here...you are way over my head here .

You and me both, chum! Except for 1st year classes, all my electronic knowledge (such as it is) is self-(mis-)taught.

Crack the books!

[Aaron Silidker]

Speaking to a mechanical engineer here...you are way over my head here .

You and me both, chum! Except for 1st year classes, all my electronic knowledge (such as it is) is self-(mis-)taught.

Crack the books!

Yea well converting a high voltage positive signal to a low voltage one is beyond me and book reading, so maybe the folks on here can help.

[Aaron Silidker]

Some success at least theoretically. Did some more research into how a CDI coil works. Should have a high voltage/longer duration charge pulse on the flywheel (I do have a very long tooth on my stock flywheel) and a lower voltage/shorter duration trigger pulse on the flywheel (I have that also just after the long tooth). Conveniently, this explains why my VR sensor has two outputs circuits. One should be to charge the capacitor in the CDI, the other should be to trigger the CDI to fire. Unfortunately for me, trigger directly off of these VR signals is impossible because both of them, at least from what I can gather, are identical signals, just go to different circuits in the CDI box.

One circuit ignores the long pulse, one circuit ignores the short pulse.

My boss at work is conveniently a PHD in computer engineering and computer science. AKA smart guy with this stuff. He said I should be able to easily clip the signal between the CDI and the coil with a Zener and a resistor. Obviously this would be a rising edge signal correct? Can I use this as a tach trigger for fuel only control with a microsquirt if I get the voltage to 12 or lower and feed it to the opto in circuit? What about amperage...is the amperage of the CDI trigger voltage fairly low?

Maybe I should just man up and go for spark and fuel all at once. I have a really nice trigger wheel ready to roll......will probably be easier than rigging something to work with the stock ignition.