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

I am trying to hook up a sensor to detect engine RPM on a small (<3hp) engine. What methods are out there to make this as simple as possible to hook up to the engine and microsquirt? I have a small optical sensor but it does not work for some reason. I have seen the hall effect sensor method used and I am curious if this works on a small scale.

What methods would you suggest for this application?

Thanks for the help.

Nathan

The engine size won't make a big difference. The most important question is if you are trying to control fuel only, or need something to control ignition too. Ignition timing needs a bit more precision.

Thanks for the reply Matt.

As of now, my ignition is being controlled via stock magneto coil (standard small engine ignition) so I would only be interested in the fuel control. I have an optical sensor that seems to be working but MT will not register any RPM. I found an issue with MegaSquirt where no rpm would be read if a jumper was not installed, I assume this only applies to MegaSquirt and is not an issue for Microsquirt though? Not sure if this is a common issue or not.

You may need a pull up, as most optical sensors are like a switch to ground and the MicroSquirt is expecting a voltage. Try wiring the OptoIn+ to 12 volts through a 1K resistor and see if that helps.

That did it! Thanks for the help Matt.

OK so now the optical sensor seems to be working but it is showing some really high rpms, like around 15k...my engine should top out at 8k. Along with the optical sensor I am using a disc with a slot in it that is mounted to the crankshaft. Anybody have any ideas why the rpms would read so high?

Since you're getting 1 pulse every rotation, tell it you have a 2 cylinder.

Thanks, I'll try that...with skepticism. It seems like that might cause other troubles? Are there any other calculations based off the cylinder quantity?

natedawg wrote:OK so now the optical sensor seems to be working but it is showing some really high rpms, like around 15k...my engine should top out at 8k. Along with the optical sensor I am using a disc with a slot in it that is mounted to the crankshaft. Anybody have any ideas why the rpms would read so high?

Nathan, you seem to have similar problems than I do (single cylinder, double RPM displayed). I will try Grippo's advice from the other thread tonight and see how it goes.

When running just fuel, the number of cylinders is really the number of tach pulses per engine cycle.