Using AE86 Tachometer & Aftermarket ECU 12v output?

[assassin10000]

Ok, I'm trying to wrap my mind around this and come up with what I consider an 'elegant' solution. What I want to do is modify the AE86 tachometer to accept the 12v+ signal from an aftermarket ECU. WITHOUT having to build/buy a signal booster.

Is this possible? Did the searching I've been doing for the last couple of hours been in vain (IE: give me a link!)?

Something similar to these ideas, is what I'm looking for:
http://www.toymods.org.au/forums/sho....php?p=1165293
http://members.iinet.net.au/~awcabren/ae86gzetacho.pdf




If not, I suppose the other option is to do tap a signal from each coil (-) and isolate with a diode and run it to the tach. Similar to what has been done on some GZE setups. As I'll be running individual coils.


Andrew

[beerhead]

Maybe the ecu is doing a positive only trigger, and if the tacho used to be points then it's looking for a 12V- Ground pulse. I'd try a "pull down" resister- wiring the 12V tach output through a 560ohm resister and to ground. Wiring the tacho to the 12V side the tacho will now get a 12V - ground pulse, simple but it works in some instances.

[assassin10000]

From what I've read up on so far the tach looks for a (+) voltage spike from the coil (-) wire/ignitor.

EDIT: I may be wrong of course... anyone feel free to correct me and show me how/why/where and what to do.

Andrew

[assassin10000]

Still trying to get a handle on this. Looking at the following places:

http://www.msextra.com/forums/viewto...f2658&start=20
http://www.club4ag.com/faq_and_tech_...considered.htm

Looks like changing the 'R4' resistor might do the job? Anyone else able to confirm this?

I'm also guessing the 1k resistor listed in the pic above for 'aftermarket ecu' would be used as a pullup if the aftermarket ecu had a 5v output?

Andrew

[jondee86]

From what I've read up on so far the tach looks for a (+) voltage spike from
the coil (-) wire/ignitor.

I think you are going to have to do the emulator with the relay coil, or the diodes plus
zenner circuit. The tach does indeed look for a voltage spike. Two diodes seems to be
enough for two x 2-post coils; you will probably need four diodes for four x 1-post coils.
This assumes that the coils are fired sequentially. If they are batch fired, then one diode
should be enough.

Cheers... jondee86

[assassin10000]

Yeah, that I'm aware of... if that's what I end up having to do. Although in the 'old' forums there was something said about that type of 'circuit' overheating and damaging the components so at one point it will stop working. Dunno how true this is or not.

Andrew

[beerhead]

Did you try a pull down circuit? I've used them and pull-ups many times on aftermarket ecu installs to drive factory points tacho's... Factory points tacho's want a 12V/ ground pulse, but your not giving it the ground part of the equation for the tacho to trigger. 10c part and it may spring to life, worth a shot IMO

[assassin10000]

I'm currently wiring my motor up... since it's not running yet I can't experiment with different circuits to make it work. I was hoping someone else had... or at least would have enough knowledge/info saved somewhere to clarify it. I'm hoping to avoid having to wire in an adapter (even though I already have one).

Again, from what I understand at the moment... it's a 12v squarewave and should ground. In any case, I can give the pulldown resistor a try if other things don't work out. But my understanding of the circuit gathered from 3 days of searching, is that the tach is triggered by the positive voltage seen from the back EMF spike when the coil fires. Which would be higher than the Tach Output of my ECU, but by how much I don't currently know.


Anyone have a oscilloscope and a running 4age (I have neither... ) ? Or maybe know/saved the info of the output of the stock tach output of the ignitor?

Andrew

[JP]

I'm 90% sure the AE86 tach will work from your aftermarket ECU drive if you just follow the PDF linked above that I compiled.

I've done similar with MX73 and GX71 tach's which were able to be driven from an aftermarket ECU after the change.

[assassin10000]

Hmmm, interesting. Any idea what the GZE ignitor tach output is?

5v or 12v tach output on the MX/GX Aftermarket ECU's?

Andrew

[JP]

the GZE ignitor outputs a low level signal. Wilbo did a similar mod to his NA JZA80 tach to accept the signal from his adaptronic. The MX73 and GX71 were running adaptronic also.

[assassin10000]

Interesting (and good to know). Nice to know that works with the adaptronic, which I think (although not sure) has a 12v squarewave tach output too.


In the mean time, I've pulled apart a spare tach to look at the circuit. Trying to dredge up what little electronics knowledge I had (and mostly forgotten) to figure this out. What I'm currently thinking will work appears similar in idea to what Wilbo did. As I 'like' what Wilbo did better since it only takes one jumper/resistor change, instead of two & a cap (less is more... and all that BS).


The PDF you compiled shows a 24k resistor on the 'pulse/tach' input, vs the original 30k. The Club4ag recommendation for the GZE tach is 15k w/no other changes. It makes me wonder what the 2nd resistor & cap change do to the circuit and how the IC works... which is currently beyond my meager electrical knowledge.


Also, according to notes/posts/info I've come across changing r1/r2 will alter the calibration/sweep of the tach. And this post: http://forums.club4ag.com/zerothread?id=68162 shows a guy that changed more/different things to get a working result including r1/r2. But further down that same post someone else says it's innaccurate pretty much confirming those two would change the calibration. So I pretty much discarded it as an idea.


Any electrical engineers around want to reverse engineer the tach controller? I can do an overlay pic of the circuit board and get all the components identified...

Andrew

[Flex]

Andrew, So you trying to connect a 12V square wave output from your after market ECU to your tachometer which is design for negative coil side signal? What after market ECU are you using? If you post some high res.images of the back side and front side of the PCB and ID the parts I can backwards engineer it.

[assassin10000]

Yes. It's a Vi-Pec V44.





Andrew

[assassin10000]

Just for shits & giggles I took apart a couple more clusters. One is from a GT-S (4A-GE equipped), the other 2 SR5 (4A-C).

Found out that R1 comes in various resistance values, based on the 3 I have, pics of one in the GZE tach mod, and reported value's on the Club4ag site. So I'm guessing it's different to adjust the accuracy of each individual tach.

GT-S #1 - 750k
GT-S #2 - 270k
SR5 #1 - 150k
SR5 #2 - 16k
GZE mod - 91k
Club4ag - 15k



Andrew