So you are saying the pulse count increase with the input voltage.

 

So you are saying the pulse count increase with the input voltage.

Yes.

 

Cool. What command in picaxe are you using to determine RPM?

 

count. then some simple conversion based on motor topology

 

That's what I figured. Is the circuit working with the LM311 negative lead grounded?

 

That's what I figured. Is the circuit working with the LM311 negative lead grounded?

Seems to be though i haven't confirmed anything properly yet. I think the LM311 is designed to work like this without negative volts (single supply) which is nice.

 

If the motor is fed by an AC voltage that goes from zero to say 12V, then maybe it's simpler to just detect when it goes near zero volts. That can be done using an NPN transistor and a couple of resistors. The transistor operates as a switch, so when the input voltage goes over about 0.7V, the transistor turns on and pulls the collector down to zero. So, rather than a postive-going pulse at the positive peak, you get a positive going pulse when the drive voltage is at the minimum. Google transistor switch (images); the collector pull-up resistor should go to the same positive voltage that the microcontroller is powered from. Resistors could be somewhere between 2k and 22k; transistor is any common small signal switching NPN.