  The LHAASO (Large High Altitude Air Shower Observatory) experiment is
proposed for very high energy gamma ray source survey, in which the WCDA (Water
Cherenkov Detector Array) is the one of the major components. In the WCDA, a
total of 3600 PMTs are placed under water in four ponds, each with a size of
150 m x 150 m. Precise time and charge measurement is required for the PMT
signals, over a large signal amplitude range from single P.E. (photo electron)
to 4000 P.E. To fulfill the high requirement of signal measurement in so many
front end nodes scattered in a large area, special techniques are developed,
such as multiple gain readout, hybrid transmission of clocks, commands, and
data, precise clock phase alignment, and new trigger electronics. We present
the readout electronics architecture for the WCDA and several prototype
modules, which are now under test in the laboratory.
