How does the wheel speed sensor in a Boeing 777-300ER work? I do have a maintenance manual that I found on Internet, but it doesn't have anything about the wheel speed transducer.

Any pics along with the information would be helpful.
From this Aviation Studies project report of group 2A2I at the University of applied Sciences in Amsterdam, for a Boeing 777-200:


  Every wheel is equipped with an anti-skid transducer (appendix VII),
  which is installed in the axle. The transducer consists of a rotor and
  stator. According to the speed of rotation, an electrical signal is
  send to the BSCU.
  
  This computer compares the rotation speed of all the
  wheels and detects when a wheel is rotating slower than the other
  wheels on the MLG. The BSCU will send a signal to reduce braking power
  when the rotation speed of one wheel reduces more in comparison to
  other wheels.


The principle is the wheel axle drives a permanent magnet within a 3-phase winding. The frequency of the signal generated is proportional to the wheel angular speed.

From B777 General Familiarization Manual:


Antiskid and Autobrake Diagram, source

Note: I initially believed the tacho-generator was a Socitec ST80, the same than on A320 (part number is C20105000). However when I wanted to provide a supporting document, I couldn't. So please take this as an assumption only until someone provides the part number from a Boeing document (I don't think there would be a big difference between B777 and A320 tacho-generator anyway).



Tacho-generator, part C20105000, source

More information: Bodet Aero. According to Bodet Aero, their tachometer equips A300, A310, A319, A320, A321, A330 and A340.

More about tachometers: TheAirlinePilots (section "Three Phase AC Electrical Tachometer").

This is a typical installation of the transducer (not a particular aircraft):


Source