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Location:
Brisbane
Registered:
May 2002
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 Tachometer Operation/Waveforms
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Sat, 03 September 2005 14:06
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Hey guys, trying to sort out the tacho in the 1jz/jza61.
I need some information on tachometers and how they work! (and if anyone gets their 'search natzi' hat out I will bitch slap you  ).
Tachometers usually get their signal from the coil -ve (this I know).
I figure that the tachometer must use the high voltage spike (EMF) that is generated due to the large inductance (coil) suddenly being GND triggered via the ECU? (is this correct?).
I've tried that coil emulator circuit floating around, which really should work as it just does the exact same thing on a smaller scale! (I tested it using a function generator and a CRO so it appears to work).
My main question is, does anyone have waveforms of what tacho outputs look like (so I know what I am trying to replicate)? And does anyone know what voltage (of the spike if my understanding is correct) is required to trigger the tacho?
At any rate I think I will acquire my CRO tomorrow and see what is going on!
Cheers
Wilbo
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Toymods Social Secretary
Location:
Sydney
Registered:
July 2002
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Re: Tachometer Operation/Waveforms
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Sun, 04 September 2005 00:49
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Wilbo,
in most cases (in fact, all) where electronic ignition is being used, the tachometer is in fact driven by the "tacho" output of the ignitor.
Do some reading on an LM2917 IC - these are essentially what's being used in your tachometer to make the needle move.
I havent messed around enough with measuring the actual waveforms to work it out for sure.... BUT - i do have a nifty little mod to the tacho itself that "should" make it work. Requires about 80c worth of parts from Jaycar
Email - thewitzl AT optusnet DOT com DOT au
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Location:
Pine Rivers QLD
Registered:
April 2005
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Re: Tachometer Operation/Waveforms
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Sun, 04 September 2005 05:12
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you were involved in the tacho boosting thread no? i thought you had it all sorted? whats exactly the problem? you want to run the A60 (not sure if there is a MA60 and GA60 so i will call it a A60) tacho off the Jz??? So your just after a booster or your after a more elaborate setup?
Sorry i am just wanting to totally understand the problem. i got my z10 ( same as A60 tacho to run the 1G-GTE which should be nearly the same) My mod cost me 50c to get mine working.
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Location:
Brisbane
Registered:
May 2002
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Re: Tachometer Operation/Waveforms
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Sun, 04 September 2005 10:36
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| THE WITZL wrote on Sun, 04 September 2005 10:49 |
Wilbo,
in most cases (in fact, all) where electronic ignition is being used, the tachometer is in fact driven by the "tacho" output of the ignitor.
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I'm not a complete dork
The igniter output a 5V square wave that goes to the tacho, this I know.
| THE WITZL wrote on Sun, 04 September 2005 10:49 |
Do some reading on an LM2917 IC - these are essentially what's being used in your tachometer to make the needle move.
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Is that in the newer dashes that are driven, or even the older style systems where the signal is taken from the coil -ve?
I was under the impression that it was the high voltage EMF spike that triggered the older (cars with single coils) tachometer?
If that is the case for older tacho's as well then simply changing the value of the resistance in this formula shold fix it? VO = VCC x fIN x C1 x R1 x K (from datasheet)...
Anyway...
| ndgcpr wrote on Sun, 04 September 2005 15:12 |
you were involved in the tacho boosting thread no? i thought you had it all sorted? whats exactly the problem? you want to run the A60 (not sure if there is a MA60 and GA60 so i will call it a A60) tacho off the Jz??? So your just after a booster or your after a more elaborate setup?
Sorry i am just wanting to totally understand the problem. i got my z10 ( same as A60 tacho to run the 1G-GTE which should be nearly the same) My mod cost me 50c to get mine working.
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Yep, just trying to use the MA61 digital dash with the 5V square wave tacho output from the igniter.
I have tried/made that circuit (tested it with a function generator and CRO and it doesn't appear to work in car)....hence I am trying to understand what is going on, and why it isn't working. I am sure it is a simple problem I am having.
In regards to that circuit (the kudos for this goes to cool1 ), if the igniter is able to sink current (Strongly suspect that it can, let's assume it has a pull up to the 5V and pulls low via a transistor to ground ), then the transistor in the circuit you constructed will gnd at the correct points in time creating the EMF spike to drive the tacho? The circuit below does the same thing, but is simpler  (the igniter internal circuit is a wild guess )
So can anyone tell me for sure how a single coil driven tacho is triggered? (gnd or the EMF spike?). Am I correct in assuming that it is the EMF spike?
Cheers
Wilbo
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Location:
Brisbane
Registered:
February 2003
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Location:
Brisbane
Registered:
May 2002
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Re: Tachometer Operation/Waveforms
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Sun, 04 September 2005 12:11
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Haha yep, the more I think about it I think that is ground triggered...(yeah stupid degree, I still know nothing  lol)
Well I suspect that it is differently triggered, not just ground triggered i.e. the voltage drop from +12v to ground is enough to trigger it, in that case a 12v square wave should work... I will get my function generator and test this as some stage.
If that is the case then it would simply be a matter of connecting 1 end of a resistor (say 1k ohm) to the battery and letting the other end get grounded by the igniter 5V square wave...this would make a nice 12v square wave (replace the relay in the above schemetic with a resistor...).
Cheers
Wilbo
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Location:
Perth
Registered:
July 2003
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Re: Tachometer Operation/Waveforms
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Mon, 05 September 2005 05:06
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Wilbo,
in my experience just a 12v square wave won't always work.
I've tested both my stock MA61 analogue tachos by hitting them with a 12v square wave of varying duty cycle. One of them worked, the other didn't.
I stuck a CRO on the -ve lead of the coil and saw back emf spikes as large as 400v.
So we are stuck with either constucting a booster circuit or modifying the input circuitry of the existing tacho.
Maybe Witzl's mod is the way to go - I'll send him an email.
Regards
Peter
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I supported Toymods
Banned User
Location:
Brisbane
Registered:
May 2002
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