Mikeys '72 Datsun 240z

[Snoozin]

Good news mate, very stoked to hear it's performing as required. Can't wait to go for a ride!!!

[mark105]

you must be well stoked. time for another track day so you can see how much better it is?

[10Speed]

I can confirm this is fast... my old 350z didn't compare... was awesome...

[10Speed]

Do a skid

Apologies for the very mediocre phone cam video work...

[Guest ProZac]

Does the original tach use the big inductive spike from the original coil for a trigger? Or is it an inductive loop type that is wired in series with the original points?

If it triggers from an inductive spike, they're usually pretty easy to get working with a 12v square wave. You just solder a jumper over the dropping resistor, which will be the first one you find if you trace the tach input signal on the PCB.

However the 350 sends it's tach signal to the dash over CAN, so there is no handy 12v square wave kicking about to use!

www.speedhut.com sell gauges that interface with the CANBus and take their required data from there, you could buy one and put it's guts inside the original Z tach?

[Guest dwlee]

If you want to keep the original tach and have had enough of code debugging you could try an AutoMeter 9117 tach adapter. It is wired in line with the 12v supply to the coil/s and uses the current pulses to produce a signal for the tach. See http://www.autometer.com/productPDF/0561C.pdf for details.

[Guest mikey]

Does the original tach use the big inductive spike from the original coil for a trigger? Or is it an inductive loop type that is wired in series with the original points?

If it triggers from an inductive spike, they're usually pretty easy to get working with a 12v square wave. You just solder a jumper over the dropping resistor, which will be the first one you find if you trace the tach input signal on the PCB.

However the 350 sends it's tach signal to the dash over CAN, so there is no handy 12v square wave kicking about to use!

www.speedhut.com sell gauges that interface with the CANBus and take their required data from there, you could buy one and put it's guts inside the original Z tach?

Yep, it uses the inductive spike. But part of that circuit I've built allows the tacho to work with a standard square wave. Buuuuuuutt as you point out, the big problem is finding a frrkn square wave to use. I tried building a rectifier out of a bunch of diodes and hooking it up to all the coils but it didn't seem to work. Having no scope made it hard to determine why.

If you want to keep the original tach and have had enough of code debugging you could try an AutoMeter 9117 tach adapter. It is wired in line with the 12v supply to the coil/s and uses the current pulses to produce a signal for the tach. See http://www.autometer...ctPDF/0561C.pdf for details.

This could work, might be the best way to go. Shame you have to hook it up to _all_ the coils, I was trying to build basically the same thing but using only one coil as the input. ANYWAY yes. I should probably just buy it and be done with it.... Maybe this arvo; last night I spent about $900 on mirrors and weatherstrip so feeling like I'm leaking money!

Thanks chaps.

[Guest Mr.Mk1]

That looks well capable in vids.

Now turn water into wine.

[Guest ProZac]

I'm assuming you're still running the standard internal igniter coil-on-plug VQ30 coils?

I've heard of people disassembling standard automotive relays and removing the mechanical switch from them to just leave the switching coil, then running the ignition signals into the switching coil. Apparently the switching coil generates enough of an inductive spike to trigger older tachometers. Maybe tie all your ignition signals together, through steering diodes, through a transistor, and into a modified relay coil, the other end of which is connected to ground. Then the negative side of that relay coil should have a nice triggering spike for your tach?

Excuse google docs skillllz:

Have to keep an eye on the max transistor blocking voltage though, so the inductive spike doesnt kill it. A BIP373 should do the trick I think, as they're pretty commonly used as coil drivers.

Or, just use the steering diodes, and hook it to your tachometer once it's had it's dropping resistor removed? I don't know what sort of current the tacho will want to draw however, and if the ignition outputs will be stong enough to drive it. You could get around that problem though, with a PNP transistor and a couple more resistors.

[Guest yoeddynz]

I wired a diodes in line with the output from each ignitor to coil lead. The othe end of the diodes all meet as one and then go through another resistor then to tach. Like this...

Another option for Hi Voltage output to a rev counter (rev counters that were fed from the coils -ve)

DigiKey part numbers:

Farnell part numbers

2N2222A = 497-2598-5-ND

1N4004 = 1N4004/4GICT-ND

1K resistor = 1.0KQBK-ND

Relay = Z2052-ND

1N5355B = 1N5355BMSTR-ND

2N5551A = 2N5551RLRAGOSTR-ND

10K pot = D1AA14-ND

2N2222A = 920-7120

1N4004 = 240-5441

1K resistor = 509-164

Relay = 127-0806

1N5355B = 933-296

2N5551A = 359-105

10K pot = 114-1404

I got the diodes off the shelf from jaycar and cost all of 3 or 5 bucks.

Not sure on what the gubbins and widgets look like in your COPs but maybe they have a similar small ignitor?

This is about where my knowledge in all things electronic ends.

Could you make a simple pick using a vr trigger and 6 tooth wheel to create a signal.

[Guest mikey]

....very smart things....

Excuse google docs skillllz:

...more very smart things...

This is more or less what I tried at one point, but without the resistor and transistor. Maybe I'll try it again...

The inductive load I can forget about actually, because I have a circuit (which works) which allows the tach to work with a standard square wave AND if I hook the tacho up to one of the coil inputs I can actually get it to move in relation to the RPM.

The ONLY problem I had was I only got it working off the ONE coil input and it would measure only 1/6th of the RPM it should.

So I tried the steering diode thing with 1N4004's but only hooked it up to 3 coils and wired it straight to the tach without the resistor or transistor. I cant remember the result, but it didn't work, I can't remember why.

But your transistor gave me a thought..... So I checked the manual and this is the example graph they have for the ignition signals:

So the signal is only around 4 volts! Which means it's amazing it registered on the tacho at all. But if hook up a PNP transistor where you have the NPN and have the tach signal on the collector, I should be sweet?

So yeah, I'll give it another shot then HUH?!

[Guest kyteler]

This car is F for fun to drive.

Thanks for letting me play with it.

[Guest mikey]

This car is F for fun to drive.

Thanks for letting me play with it.

No worries mate, pleased you liked it!

[Guest ProZac]

Using a PNP with the diodes connected to the gate wont work, because the diodes will never let current flow away from the base, so it'll never turn on. Using a P-Channel MOSFET should work, but you'd need to tie the gate to ground through a 10k or something so the charge has somewhere to go when none of the diodes are on.

Hmmm, if you can trigger your tach from a standard square wave, then the steering diodes should work, it's exactly how it's done in all the aftermarket ignition modules I've pulled apart in last couple of years. If you can get that to reliably work, then I say we forget about all the coil switching nonsense and focus on square waves.

I can see an issue however, with a 6 cylinder, if the RPM and dwell are sufficiently high, you might get overlap in the signals, and pulses will get lost, eg: 6 cyl 4 stroke = 3 ignition events per rpm, at 7000rpm, you've only got 2.86ms between ignition events, and its possible the dwell be longer than this, so the ouput of the steering diodes will always be high.

These are pretty cheap:

http://toolboom.com/en/Articles/DSO-Nano-DSO201-Pocket-Sized-Digital-Oscilloscope-Review.html

and would be enough for most automotive diagnosis jobs, worth having in the toolbox I reckon, for just this sort of thing .

[Guest mikey]

These are pretty cheap:

http://toolboom.com/...ope-Review.html

and would be enough for most automotive diagnosis jobs, worth having in the toolbox I reckon, for just this sort of thing .

You're right. I weighed it up before but was nervous they'd be shit. BUUUUTT I just bought it! I reckon it'll pay for itself pretty quickly.

Once it arrives I'll try the steering diode thing and see where we stand.

Thanks for all the help! This electronics thing is all very new to me.

[Guest ProZac]

Anytime man, much lub for your car, its pretty much my dream body/engine combo . I have this thing about getting factory tachos working with engine conversions.

What circuit have you got that gets it running off a square wave?

[mikey]

What circuit have you got that gets it running off a square wave?

http://www.dinoplex.org/tachoconversion/index.html

I got a bunch of these boards printed and enough components to build a few. In most situations it'll mean you can run a stock tacho off anything with digital ignition signal.

Also, the scope turned up yesterday so I was really looking forward to hooking it up and getting my tacho working, however, some scum broke into my car and stole it last night.

So now I have to buy another one.... Thieves are just great.

[mikuni]

oh well, at least the joke will be on them when they can't figure out where their sim card goes.

[mikuni]

Actually, it might be cool to move all this tacho talk to a dedicated thread? Seems a few people are doing later model engine conversions now and having similar issues. I can't even get my tacho working with an aftermarket ecu and no idea where to start.

I'll split the tach related posts into a tacho tech thread later, if you're happy with that Mikey?

[xsspeed]

"diss gps is shit bei"

Also, keen to learn more re tacho stz (and electronics in general) so would support Brad's suggestion