Wiring diagram interpretation

[thegreatestben]

I'm trying to figure out how to get the mitsi ignitor I've got works in terms of the output to the tacho.

I've got the factory diagram:

I took it to an auto sparky to just check my theory before trying it and killing things.

I assume that diagram is suggesting that I need to put 5v into the pin no.4 (which is labled tac on the ignitor)

He seemed to think this was odd. I was wondering if any of you chaps knew?

I've tried hooking the factory tacho wire from the car loom straight to the ignitor and it doesn't even move.

[Ned]

Looks like thats just a voltage divider with the Anode of the diode going from the middle of the divider (109) to pin 4

Where does 109 come from?

Got a better quality pic? Hard to see

[thegreatestben]

109 is the ecu, that strip along the bottom is all ecu

[thegreatestben]

http://i118.photobucket.com/albums/o97/ ... ires-1.jpg

[barf]

wasted spark FTW! I use a similar ignition module on my 4G93 turbo

that 5v probably just indicates the ECU has a 5v pull-up to sense the tacho (ie you should see 5v relative to sensor ground on pin#109, when the circuit is open/unloaded).

here is an example from megasquirt manual, you could implement it this way also, assuming the tacho is not looking for a logic-level pulse

http://www.msextra.com/doc/ms2extra/MS2-Extra_Hardware.htm#tachoout

[thegreatestben]

Might just do it that way.

Definitely need this going before trackday

[barf]

what sorta tacho are you hooking up? vehicle's original tacho? (what car?)

[thegreatestben]

Yup original vehicles tach.

1988 Toyota MR2 - AW11.

Originally had single coil and ignitor and tach took signal off've coil -ve

[barf]

looks like that ignitor outputs logic levels and my dash (CM5A) measures RPM as logic-level pulse from ignitor/ECU - not from coil. so that tacho output from the ignitor probably won't drive your tacho, that circuit with the zener is the ticket.

[Spencer]

Yup agree with barf build the zener circuit

[thegreatestben]

looks like that ignitor outputs logic levels and my dash (CM5A) measures RPM as logic-level pulse from ignitor/ECU - not from coil. so that tacho output from the ignitor probably won't drive your tacho, that circuit with the zener is the ticket.

Sorry I just checked the wiring diagrams for my car and it was originally getting it's signal from the ignitor.

Still use zener?

[barf]

well you might be lucky here, if the signal from the toyota ignitor was the same or similar enough (can't recall) then it could just wire straight up OK.

the theory is the same in either case, a tacho identifies a revolution by observing a momentary break in the ignition circuit. logic level tachos may invert this signal and/or represent it by frequency of a square wave

forgive the pbrush.exe diagram

[thegreatestben]

Yeah so far I've got nothing by trying direct wire up.

I haven't ruled out the ignitor being faulty, it was a 2nd hand unit.

I can't see why the tac function would be faulty though, the car I nicked it out've was pretty tidy.

[Ned]

Get a muli meter (with a frequency setting) and see if you are getting something from pin 4. Would be better if you had a scope, but not many people do. Will check out that diagram again now

[thegreatestben]

Put a scope and multi meter on it and got nothing.

Hence thread.

Sorry for not providing details

[barf]

i think you might not observe anything on that wire from the ignitor because it doesn't output a voltage but switches to ground instead, there was a 5v pull-up in the ECU on that diagram for this purpose.

[Ned]

Hook 109 up to 4 and you can get a 5V square wave for a tacho from there. Now you will have to convert from a 5V signal to full level.

Does 109 HAVE to be connected to 4 for the car to work? Because if not, you could get a 12V supply, hook it up to one side of the coil that you stripped from a 12V relay, the other side to 12V and then connect the tacho to pin 4.

I'm not sure if this will work, but thats because i'm not sure what the signal into the tacho is supposed to look like. Ryan had the same issue and i made him a circuit that used a pullup resistor instead of the coil and that didnt work. The drawing he found on the net said to use the coil from a 12V relay.

[thegreatestben]

109 doesn't exist in my car.

That's how the coils are wired up in the galant they originated from.

The ignitor works as an ignitor without 12v+ supplied, the tac doesn't apparently. But mine just doesn't work.

The internet made this sound easy prior to asking here

[Ned]

Uploaded with ImageShack.us

Diode is probably not needed though

[Mike-e]

build the zener circuit