Feature Request - Tach Change..

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ErnieJones
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Feature Request - Tach Change..

Post by ErnieJones »

My stock tach reads half the actual RPM. I posted about it and apparently this is caused by using sequential injection.

Tuner Studio has an option to reduce the tach output by half - would it be hard to add in a firmware option to double the tach output so that people can use sequential injection with a stock tach on a vehicle that never had OE sequential injection?

Seems to me this would be useful for more folks then just myself. Perhaps it's a natural outgrowth of sequential injection support?
Thanks you;
Ernie
slow_hemi6
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Re: Feature Request - Tach Change..

Post by slow_hemi6 »

Find the Manuals up top under Quick links: Manuals. :RTFM:
Cheers Luke
ErnieJones
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Re: Feature Request - Tach Change..

Post by ErnieJones »

Yeah, I never did hear back from James about it in that thread so I thought that perhaps it could be addressed with Tuner Studio. Turns out, it has to be addressed at the firmware level.

But thanks for playing :lol:
Thanks you;
Ernie
jsmcortina
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Re: Feature Request - Tach Change..

Post by jsmcortina »

Your "tach doubling" is only applicable to single cylinders using MAP sensing to switching from wasted spark to COP. It does not apply to sequential in general.

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dontz125
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Re: Feature Request - Tach Change..

Post by dontz125 »

If it can't be done in firmware (or isn't cost-effective for one user), it can be done in hardware. Simple frequency doubler circuits won't work because of the wide range of frequencies involved, from 2Hz (120 RPM at cranking) to 200Hz (12000 RPM as the valve keepers spit off and the rod comes out to play). This would be a fairly complex beast, involving an LM2907 Frequency-to-voltage converter, a DC-DC voltage doubler (with op-amp based precision rectifiers to avoid losses), then an AD654 voltage-to-frequency converter. Each stage would have its own IC plus resistors and caps, all specifically selected for the duty at hand.

Or you could run wasted spark ... :lol:
QuadraMAP Sensor Module -- PWM-to-Stepper Controller -- Dual Coil Driver
Coming soon: OctoMAP Sensor Module
TTR Ignition Systems
ErnieJones
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Re: Feature Request - Tach Change..

Post by ErnieJones »

My thinking was along two lines;

1) It would apply to anyone on a single (these are usually lower end bikes without a cam sensor or sequential) - so not just for me :D

2) All it would take is something like 'Multiply Tach Signal Output x2' :D

I got thinking like that because I saw an option in Tuner Studio to cut the tach signal in half - which works using MAP-based sequential. The signal does get cut in half. So my assumption was 'do the same - but double it' :D - no big deal. Apparently, it is :?
dontz125 wrote:...Or you could run wasted spark ... :lol:
It's looking like that's what folks will have to do if they don't have a cam sensor. It's not the end of the world but it seems to kind of defeat the purpose of using map-based sequential in an application as described :cry:
Thanks you;
Ernie
dontz125
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Re: Feature Request - Tach Change..

Post by dontz125 »

ErnieJones wrote:2) All it would take is something like 'Multiply Tach Signal Output x2' :D
Unfortunately, that will take very careful scheduling and is a non-trivial exercise. The problem is that the 'tach' output signal is triggered every spark pulse. It is trivially easy to then say, for half-speed, 'trigger every OTHER spark pulse.'

It will take careful timing to send a tach pulse halfway BETWEEN spark pulses, and may require rewriting the code to allow 'wasted spark' operation with 'half-speed' spark pulses.
QuadraMAP Sensor Module -- PWM-to-Stepper Controller -- Dual Coil Driver
Coming soon: OctoMAP Sensor Module
TTR Ignition Systems
ErnieJones
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Re: Feature Request - Tach Change..

Post by ErnieJones »

I think that's what James was getting at - it's not a trivial thing. I have no idea as to how the underlying software works but it seems to not be an easy thing to do.

Like you said, there's always wasted spark. Not as nice as sequential but at least there's a choice. You can run sequential but it just means 6K is really 12K and you either have to live with it, or replace the cluster, or go to wasted spark. At least there are choices and a work-around.
Thanks you;
Ernie
dontz125
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Re: Feature Request - Tach Change..

Post by dontz125 »

You still have sequential injection, and that's where the benefit lies. With a single, there isn't much to gain between COP and wasted.
QuadraMAP Sensor Module -- PWM-to-Stepper Controller -- Dual Coil Driver
Coming soon: OctoMAP Sensor Module
TTR Ignition Systems
Laminar
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Re: Feature Request - Tach Change..

Post by Laminar »

I'm going to pile on and also express my interest in this feature.

I'm putting an 8 cylinder engine into a car that originally had a 6 cylinder engine, and I'd like to retain the stock tach. The guys doing LSx swaps and keeping the stock GM ECU are able to adjust their output pulses to match up with the speedo.

If this won't happen inside the Megasquirt, Dakota Digital's SGI-8 will take a tach input and allow you to adjust the output for 4, 6, 8, or 10 cylinder output.
MS2tester
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Re: Feature Request - Tach Change..

Post by MS2tester »

not an electronics expert but
maybe something like this?
ErnieJones
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Re: Feature Request - Tach Change..

Post by ErnieJones »

I think these are issues that need to be addressed in firmware - that way they can be changed at will :D
Thanks you;
Ernie
dontz125
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Re: Feature Request - Tach Change..

Post by dontz125 »

"At will"? How often do you plan on changing your tach ratio?!
QuadraMAP Sensor Module -- PWM-to-Stepper Controller -- Dual Coil Driver
Coming soon: OctoMAP Sensor Module
TTR Ignition Systems
ErnieJones
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Re: Feature Request - Tach Change..

Post by ErnieJones »

dontz125 wrote:"At will"? How often do you plan on changing your tach ratio?!
Just like I change my underwear - daily :lol:

I was trying to think from the perspective of the wider community - not just my own specific needs :D
Thanks you;
Ernie
mazdaspeed
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Re: Feature Request - Tach Change..

Post by mazdaspeed »

Why not use the tacho circuit seen in the ms1 extra manual where you get all the coil driver signals and run it through some diodes?
Laminar
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Re: Feature Request - Tach Change..

Post by Laminar »

Just a quick note - glancing through the 1.4.0 firmware changes, I noticed this line:
A fully variable tacho output is now available to correct for inaccurate tachos or differing cylinder counts.
I hope to upgrade and try it out today or tomorrow.
ErnieJones
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Re: Feature Request - Tach Change..

Post by ErnieJones »

Assuming that does the trick it would be nice to see it ported to MS2 :mrgreen:
Thanks you;
Ernie
Laminar
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Re: Feature Request - Tach Change..

Post by Laminar »

It works!! I'm using a 6-cyl E36 gauge backplane, an M3 front face, a 4-cyl E36 tach servo, and the 6-cyl tach scale.

I knew that 6500rpm on the tach was 4500rpm for real per my shift light, so I set scaling to 69.2% and it worked perfectly!
ErnieJones
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Re: Feature Request - Tach Change..

Post by ErnieJones »

That's awesome news - Way to Go! :yeah!:
Thanks you;
Ernie
mariob
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Re: Feature Request - Tach Change..

Post by mariob »

I know i set up my 1-cyl bike with a 2-cyl ini long time ago because of the tach output having only half the frequency needed. I simply did not use the second ignition output and it worked nicely. (although it was spark-only)

Best regards, Mario
Peugeot 106 Sergio_Tacchini, 1124cm³, MS2/Extra pre3.3alpah15, E85
Citroen AX, 954cm³, MS2/Extra pre3.3alpha15, E85
Peugeot 106 Rallye, 1298cm³ ... waiting for ITBs and full sequential injection
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