microsquirt for fuel only; triggering from coil

[GMax]

Gooday folks

I am wanting to use Microsquirt for fuel only to start with, once working I will look into going fuel and spark. I have all of my sensors wired up, including OPTOIN+ (Ampseal pin #30) to the coil's negative terminal through a diode, and connect the OPTOIN- (Ampseal pin #31) to a 12V source throgh a 1k resistor. This is after many hours of reading of the problems with triggering directly off the coil.

Here http://www.msextra.com/doc/general/tachin-us3.html they do no mention the resistor or diode so am unsure if I sould remove them and risk blowing up the unit.

No mater what I try I can get no RPM to show up, I have tried various settings under the ignition setup but nothing shows in the software. I even tried quickly earthing OPTIOIN+ to try emulate the coil but nothing. I have checked and rechecked the wiring, disconnected OPTIOIN + and - and connected a test lamp which flashes as the engin is cranked, do I have the wrong settings in TunerStudio or where do I go from here.

My MSQ is attached, all other sensors are calibrated and working fine.

[GMax]

After reading the first 40 or so pages of those posts (10 posts per page) that come up when i searched I am even more confused,

some say leave OPTIOIN - floating and cut the wire off,
some say earth the wire, YES on the V3 as well as they had no spark untill they did that
the microsquirt manual does not say use a diode and resistor,
the posts in the forum say you need a diode and 1k resistor to prevent blowing the MicroSquirt
some say you need to replace R20 as it keeps blowing?
some gave up and added a trigger wheel

Can it really be all of the above? I don't have 2 coils, just one. I don't have a trigger wheel and EDIS was never an option in Oz.

I purchased all the parts and sensors from a listed supplier as a complete set to make sure I didn't have any strange issues with unknown parts.


Do I bypass the resistor and diode as per the V3 MicroSquirt QuickStart Guide and risk burning out the MicroSquirt and if it blows up where do I stand.

[dontz125]

Without knowing which wiring is / isn't working on a particular try, it's hard to explain / suggest why your example isn't working.

That said, I've heard very good things about this particular arrangement:

engine_speed_trigger.jpg (14.13 KiB) Viewed 4523 times

Most of the fixes etc that you're reading about are trying to tame the flyback pulse, with its enormous voltage spikes and ringing on. By pointing the diode AT the coil with a pull-up resistor between the diode and the OPTO+ pin, this set-up eliminates the flyback and ringing entirely; all the MicroSquirt sees is a clean 12v square wave. OPTO- simply goes to ground.

Note that this particular schematic was for a 4-cyl with a 2-coil wasted spark; for single coil you only need the one diode.

[GMax]

Hi Mate

Thanks for the reply, that is exactly what I did, 1K resistor to 12V on the OPTIOIN - and diode on OPTIOIN+ to coil but get no RPM.

Troubleshooting was to leave the resistor and diode in and connect a test lamp (and removing the connection to the MicroSquirt) which resulted in the test lamp going on at each pulse. So sucess, the diode was installed correctly and the resistor is working and not open circuit. However, connecting the OPTIOIN's again still results in no RPM.

Reloaded firmware, still same, rechecked install documentation but saw there was no reference to the diode or resistor so not sure if to try that. I am in OZ and the supplier of the MS is in USA so not keep to blow anything up.

[dontz125]

that is exactly what I did, 1K resistor to 12V on the OPTIOIN - and diode on OPTIOIN+ to coil

Look at the diagram again, read what I said:

• diode from OPTO+ to coil, band towards coil
  +12v pull-up resistor between diode and OPTO+
  OPTO- to ground

[GMax]

Wait what?

Most of the fixes etc that you're reading about are trying to tame the flyback pulse, with its enormous voltage spikes and ringing on. By pointing the diode AT the coil with a pull-up resistor between the diode and the OPTO+ pin, this set-up eliminates the flyback and ringing entirely; all the MicroSquirt sees is a clean 12v square wave. OPTO- simply goes to ground.

That is the opposite of what I have as well as the manual. So the OPTIO- to ground and the diode to OPTIO+ with a pull up resistor to 12V.

I am off to try that now and will let you know if that helps.

Thanks

[GMax]

You sir are a Genius! Thank You, Thank You, Thank You.

For the first time I see RPM and she pured to life, rich as a pig but started. The wiring is down and dirty (everything else is done properly with solder and heatshrink) but that is easily fixed.

My humble opinion is that this should be linked to for the triggering from a coil as it just works, at least it should get a mention in the Quickstart Guide here http://www.useasydocs.com/details/coiltrig.htm.

On a side note the link to that page from http://www.useasydocs.com/details/wire.htm is broken and you currently need to Google it to find it is how I ended up with all the wrong ways as to how to connect it.

Again, Thank You

[dontz125]

[Laugh] No genius, just someone who's been reading up on these toys for a while. The fellow who created / developed that circuit goes by matt_gsxr. He used to hang around the Extra forum, but I haven't seen any posts from him in quite some time.

Glad it worked for you!

[GMax]

Still, I have been reading for a few weeks but wasn't sure which was correct. I knew there must a correct way but not which was the right one.

Genius still stands as you knew the right one and no damage was caused to the MicroSquirt.