[time-nuts] Building a mains frequency monitor

[Hal Murray]

cfharris at erols.com said:
> A more modern name for a synchronous motor is a permanent magnet stepper
> motor.  Any PM stepper, and a couple of microfarad capacitor becomes a
> synchronous motor when connected to the power line. 

The old pre-digital way of generating a rotating field for a synchronous 
motor was a shaded pole.  They worked well for low torque applications like 
clock motors.  I saw plenty of them when I was a kid.  The rotor was hidden 
in a package with the first layer of gears.  I assume it was a permanent 
magnet but never took a package apart to verify that.

Good pictures here:
  https://en.wikipedia.org/wiki/Shaded-pole_motor


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