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Tacho


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#1 tux

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Posted 01 June 2020 - 06:17 PM

Saw Scott's thread on the tacho.. I don't want to jumble up his thread as I'm using an AEM


The gpio pins are grounds on the AEM.  According to their faq, for a negative side coil driven tach, I need a 12v square wave.

I tried using a 2.2k resistor to pull the AEM trigger up to 12v, however, I got nothing


The gold box is gone, so that isn't doing it.

Anyone have any ideas of how to make the tach fire from this setup?  

I'm not looking to tie into the coil driver I want to leave that circuit alone.





#2 ucw458

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Posted 01 June 2020 - 07:49 PM

iirc on my AEM the trigger for the LS2 coils is 5v.  I'm using 4 coils.  I tied all 4 trigger wires together using 4 diodes.  The output of the 4 diodes is combined then sent to the tach.  My tach works fine on that 5v signal.
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#3 scott87star

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Posted 01 June 2020 - 07:50 PM

Wiring diagram of what you tried?
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#4 tux

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Posted 01 June 2020 - 08:39 PM

Scott,
Essentially this
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I have an i/o from the AEM ecu running to the tach line in the harness I think it was blue on the gauge cluster harness and yellow/white(?) On the body side of harness.  The original white wire in the engine bay is removed.


Ucw, I know how yours is setup actually.  I don't want to snake anymore wires around :)

#5 scott87star

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Posted 01 June 2020 - 09:12 PM

Can you find a scope?  Hard to diagnose without looking at the signal.
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#6 tux

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Posted 01 June 2020 - 09:27 PM

I got a scope, I guess I need to set that up.

#7 ucw458

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Posted 02 June 2020 - 12:11 AM

View Posttux, on 01 June 2020 - 08:39 PM, said:

Ucw, I know how yours is setup actually.  I don't want to snake anymore wires around :)

I didn't have to run wires for that.  I tapped into the ignition trigger wires next to the AEM and connected the output to the factory ECU ignition signal wire.  The whole thing is about 6" long and behind the kick panel.





Your pull up resistor may be holding that wire in a high state so the tach never sees the pulses.  It doesn't matter if the AEM is pulsing on/off, the pull up resistor is holding the wire in the on state.
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#8 scott87star

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Posted 02 June 2020 - 08:34 AM

The gpio are ground switching so its either ground or floating, your schematic should produce a signal.  However the resistor value dictates the shape of the signal which needs to be a nice square wave which is why we want to see it on a scope.
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#9 tux

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Posted 02 June 2020 - 11:09 AM

So I get a nice square wave.

I pulled up to 12v using 2.2k resistor and it didn't work.

I switched that out for a 10k pots, when it's turned down to 1k get 12v to my tach.

But when I start the car the most I get out of her is 3v (when the ecu is pulling to ground).

Hmmm.

#10 scott87star

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Posted 02 June 2020 - 12:35 PM

Did you try messing with the pot with the car running?
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#11 tux

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Posted 02 June 2020 - 12:52 PM

Yea

#12 tux

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Posted 02 June 2020 - 02:37 PM

Worked using a mosfet

#13 tux

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Posted 02 June 2020 - 03:39 PM

Bs170 n channel mosfet
Pinout
gate: gpio 1
drain: tach to 2.2k resistor to +12
Source: ground





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