| Author | Topic |
|---|
Location:
Brisbane
Registered:
May 2002
|
|
Re: Tachometer Operation/Waveforms
|
Sun, 04 September 2005 10:36
 
|
 |
| 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.
|
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.
|
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.
|
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
|
|
|
