MicroSquirt.com read only forum (Jan.15,2018)

What size diodes do I use with this setup?

I used a slight modification of this circuit when I built my fuel-only Microsquirt Kawasaki EX-250. It has performed flawlessly for 6 years now.

As I said, it's been a long time so I can't remember the exact type of diode but I think I used either "1N4003" or "1N4004" in the 1 AMP size. The "03" blocks up to 200 peak inverse voltage and the "04" blocks up to 400 peak inverse voltage. Knowing my tendency to hedge toward the safe side I'd bet my circuit has 1N4004 in it.

So you're working on a fuel-only configuration, right? That's what this ignition sensing circuit was created for. What kind of engine are you putting this circuit on? Just to be sure that you are forewarned, the drawing you posted may not be correct for your application. You might have to modify it slightly to get the "signal that comes once every 360 degrees of engine rotation" that you need for input to the OPTOIN on the Mega/Micro squirt ECU.

On my application, which is a wasted-spark 2 cylinder flat-plane crankshaft motorcycle engine, I only needed 1 branch of the circuit (one diode and one resistor connected to only one coil) because on my engine each of its two coils fires every 360 degrees (but they fire 180 degrees out of phase with each other). The same would be true for a wasted spark 4 cylinder engine, it too would only need one branch of the circuit.

I am using this as a fuel only for a 1983 Honda CB1100F four cylinder motorcycle. I have the toothed wheel and sensor for final configuration but I wanted to get things working with the Dyna 2000 Ignition system that I have on it now.

Are you sure about the single signal for every revolution?
http://www.microsquirt.com/viewtopic.php?f=89&t=25721

What wattage rating should I use for the resistor?

The resistor can be whatever you've got, 1/4 watt will do. I think I used 1/2 watt in my version of this circuit. Part of the beauty of the "matt_gsxr" circuit is that it delivers a nice, smooth, low-amperage signal to the microsquirt's OPTO circuitry. The diode in this circuit is doing the hard work, blocking out all of the coil's crazy electrical-storm side effects, while the resistor is just loafing along. This protects the R20 resistor in the microsquirt from getting burned out, which regularly happens when people use other methods to direct-sense the coil.

Not sure about your interrogative,

Are you sure about the single signal for every revolution?

Because 1 signal per 360 degrees of engine rotation is exactly what the microsquirt is looking for in a fuel-only setup. And that is where people make most of their mistakes when implementing this circuit.

I'm just trying to warn you ahead of time that if you wire it up exactly as drawn in the diagram (in your original post) you may end up with a signal every 180 degrees of crankshaft rotation which would cause the engine to be over-fueled and the Tuner Studio will indicate 2 times the RPMs. You know better than me how your Dyna 2000 ignition works (i.e. wasted spark, firing 1&4 and 2&3 together, or firing each coil individually) so it's up to you to figure out how to extract only the needed signal that the OPTO circuit needs.

But, yes, without a doubt, your goal is to get 1 signal per 360 degrees of engine rotation.

I disagree. I'm having the worst time finding a cite, or phrasing WHY I believe this, but my understanding is that you basically want one pulse per ignition event per engine cycle - a twin has 2, a four has 4, a V8 has 8. Fueling issues should be solved by setting the req_fuel and # squirts options properly. I am actually surprised that the TS RPM indicator shows double; that may be a discussion to have with Phil.

I agree that a twin firing wasted spark should use a single branch of the diagram as shown. I disagree that a 4 should use the same schematic, but suggest instead that it use the diagram as indicated - that is in fact the service for which it was designed.

I agree that a twin firing wasted spark should use a single branch of the diagram as shown. I disagree that a 4 should use the same schematic, but suggest instead that it use the diagram as indicated - that is in fact the service for which it was designed.

Matt was working on a 4-coil GSXR 600 motorcycle engine.

The matt_gsxr circuit is for a 4-coil sequential ignition engine, one coil for each cylinder and an ignition system that only fires each cylinder's coil once every 720 degrees of engine rotation (the 4-stroke engine cycle). As drawn, the matt_gsxr circuit on a 4-coil 4 cylinder engine will result in a signal being sent to the Microsquirt's OPTO circuit only once every 360 degrees.

However, if the Original Poster of this thread (mechyank) is working on a four cylinder motorcycle engine that has only two coils then it is a wasted spark engine and each of those two coils will fire twice in every 720 degrees of engine rotation.

A wasted spark parallel twin with a flat-plane crankshaft and a wasted spark inline 4 cylinder with a flat-plane crankshaft are exactly the same with regard to spark output. Both of these wasted spark engines have two ignition events in every 360 degrees of rotation.

The wasted spark parallel twin w/flat-plane crankshaft has two coils... same for the wasted spark inline 4 cylinder w/flat-plane crankshaft.

The wasted spark parallel twin w/flat-plane crankshaft fires its two coils 180 degrees out of phase with each other.... same for the wasted spark inline 4 cylinder w/flat-plane crankshaft.

If you hook up the matt_gsxr circuit to both coils on either of these engines, Tuner Studio will show 2X the RPMs that the motorcycle's stock tachometer shows (if you haven't messed with the Tach's OEM wiring, that is).

A flat plane 4 fires 'a' coil every 180°. For most Japanese bikes, in wasted spark it fires 1-4/2-3/1-4/2-3. For a sequential COP installation, it fires 1/2/4/3. Either way, you get 4 ignition events per engine cycle.

Yes, this is true...

A flat plane 4 fires 'a' coil every 180°. For most Japanese bikes, in wasted spark it fires 1-4/2-3/1-4/2-3. For a sequential COP installation, it fires 1/2/4/3. Either way, you get 4 ignition events per engine cycle.

... but what I've been saying, what I was trying to explain to the original poster, is that in a fuel-only microsquirt application you don't want to feed 4 ignition events per engine cycle (720 degrees of rotation) to the microsquirt's OPTO circuit. Instead, you want to feed it 2 ignition events per engine cycle, i.e. 1 event for each 360 degrees of engine rotation

... because in a fuel-only setup the microsquirt thinks/reacts to every input to the OPTO circuit by triggering the injectors in whatever way you've configured the firmware to use, i.e. by whatever setting of the req_fuel and # squirts and simultaneous/alternating options you have chosen. And, a further reason to limit the OPTO inputs to 1 per 360 degrees of rotation is that in a fuel-only setup the Microsquirt is programmed to interpret each OPTO input signal as a Tach signal which is used in Tuner Studio to display engine speed.

(We'll never know why Matt drew his circuit the way he drew it. The truth is that it isn't correct for either a COP or wasted spark 4 cylinder engine.)

I disagree. The coil -ve trigger hearkens back to the earliest days of the MegaSquirt, when the flyback pulse of the single coil on a distributor-fired V8 was the only trigger signal possible. Thus, the MS expected one trigger pulse per ignition event; a V8 produces 8 pulses per engine cycle, an inline 4 produces 4, and a twin produces 2.

I agree with you completely that a twin using wasted spark coils should only trigger from a single coil. A 4, on the other hand, should use both coils, and the injector and engine constants should be adjusted to provide suitable fueling. If this cannot be achieved, there is something wrong with either the tune settings, the hardware, or the firmware.

I await correction by a dev. I looked through the MegaManual and the uS manual, and could find nothing definitive on this matter.

That all makes perfect sense. I didn't know the history of the issue.

I guess I have always had a problem of limited perspective on the issue, because I've only ever dealt with a fuel-only parallel twin. Nothing bigger or more complex. It never occurred to me that in fuel-only mode when you told the Microsquirt how many cylinders are in the engine, it then adjusts the number of ignition events it is looking for per engine cycle. I had always operated on the assumption that in fuel-only mode the Microsquirt was just looking to know the basic RPMs of the engine.

This makes today a "live and learn" event for me.