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Another tach signal generating question

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WestOzXJR

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Hi everyone, I'm Victor on the west coast of Oz.

I'm a motorcycle race engine tuner developing a 4 cylinder motor with engine management duties handled by a hacked Yamaha factory ECU. Although I'd considered switching to an after market ECU for ease of tuning, some of the features of this engine can't be driven by most of the common "motorsport" type ECU's so I've committed to persisting with the factory original but a relatively minor technical issue is plaguing forward progress.

Now I believe this issue is fairly easily overcome but my knowledge of what I think are relatively minor electronic modifications required is not my main area of expertise...

I've been reading threads here for some time now about generating and buffering tachometer signals from various problematic perspectives and I think my "issues" are unique and require a different approach to those who have come before me with such questions, so hence I'll present my problem and hope someone can assist me...

Stated as simply as I can in one sentence, my issue revolves around being able to get a "clean" rpm signal that my after market; rpm, air/fuel ratio, temps and throttle position data logger can accurately interpret.


The engine in question runs a multi-toothed magnetic reluctor trigger wheel with missing teeth on one section of the wheel that provides crank position information to the ECU. So this signal is not really interpretable by the data-logger.
See figure 1.4: **broken link removed** represents the signal this set up generates which the ECU can interpret just fine but this means scattered mumbo jumbo to the data-logger.

In addition to actually trying the crank trigger signal (which resulted in rpms in the millions at idle!), what I have tried is:
ignition coil low side (-) triggered by the ECU,
injector drive (-) triggered by the ECU.
Neither of these are acceptably readable/accurate.

As a qualified motor mechanic, I understand the spikes coming back down the coil (-) side and the data-log plot line clearly shows these spikes are the issue when using this source for the signal.

The injector drive signal is useless too as the variable width of the pulse and the ECU's characteristic of shutting off the fuel on the over-run has the signal going AWOL and is therefore unacceptably inaccurate.

No doubt the ECU does produce a tach signal for the standard instruments, BUT it's transmitted along with other information down a ONE wire data link to a chip in the dash and extracting that information is not a viable option at this point in time although it is a long term "want to learn how" project...

Now the manufacturer of the data-logger says, "the device will work on any ignition system on any vehicle", so approaches to them have resulted in no usable assistance.

They say the rpm signal trigger can be any one of a wide range of source voltages but are not being specific as to what the ideal voltage or waveform the device is actually designed for.

Their current suggestion is to attenuate the coil low side (-) to obtain "acceptably clean" (read acceptably inaccurate) signal. However my main argument against that is: to alter that signal on ONE coil is to put it out of balance with the signal to the OTHER coil and hence probably trip the ECU into a fail safe mode/trigger an ECU fault code - which I can't even know to be occurring because I don't even have the standard dash....

However, what I do know is the "success stories" I've read seem to have one common link - which is the signal source utilized was 0-5 hall - which would co-relate with other "required" signal inputs to the data-logger such as; TPS, temp, O2 sensors are all 0-5volt.

Now as I see it, the solution to my problem is in 2 parts:
1) I've ordered from the US an Autometer tach signal generator for coil-pack/distributor-less ignitions, that when wired in series with coil (+) reads the current ebb and flow to produce an apparently accurate tach (-) signal. This may be enough for the dat-logger to read.

2) However near future plans will eventually require a 0-5 hall-like tach signal so I need to convert this (-) pulse from the Autometer signal generator into an emulated 0-5v trigger signal.

That is what I need assistance with - a circuit to produce this 0-5v square wave signal from the Autometer (-) tach signal...

Does anyone have any advice or design ideas for this problem?

Thank you for you time and now I'm finally finished this post I'll look for the "donate to this site" button in appreciation of all the fine assistance you folks seem to freely give out...

kind regards,

Victor.
 
I did this for our race cars and an intake motor control and digital dash I made. You can likely adapt the circuit to work off of your coil. They will provide a perfect 0 5Vdc square wave output. One is a divide by two so beware.

Raptor also has a lot of good information Tach Installs

There is a lot of information on egauge as well:
**broken link removed**
 

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  • Tach Circuits.pdf
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  • Tachs Install.pdf
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TTL tach conditioner

Here's another that's opto isolated for max reliability.
 

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  • tach-extract.jpg
    tach-extract.jpg
    208.5 KB · Views: 321
Thanks very much for that - very very helpful and useful info...

The ATM 9117 referred to in the Eguage Installs link is exactly what I've ordered.

The circuits in Tach Circuits.pdf look like they're exactly what I need to drop on the back end of the ATM to produce the 0-5 signal.

So I'll call that problem solved and head down that path - thanks once again...
 
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