Detail for my Mk2_3phase_RFdatalog_1.ino sketch

This sketch is intended to run on my "Mk2 3phase" PCB.  Voltage and current are 
repeatedly sampled for each phase in turn.  Every mains cycle, the average powers 
for the three separate phases are combined and used to update an "energy bucket".
This "energy bucket" represents the overall energy state of the premises. 

Any surplus energy is made available to dump-loads.  This sketch supports 
three dump-loads which can be on any phase.  The loads are activated in order 
of priority.  An external switch can be used to select between two pre-set 
priority sequences.

Datalogging is supported.  This records the average power and Vrms voltage on 
each phase every few seconds.  This data is always available at the Serial 
interface.  If the RF facility is enabled, this data is also transmitted by RF. 
RF is enabled by including the literal definition for RF_PRESENT near the top
of the program.  If this line is commented out, RF is disabled.

To minimise the rate at which the loads are cycled on and off, this sketch operates
with a single-threshold anti-flicker algorithm.  The optimal rate of cycling is 
determined by the supply meter so may need to be adjusted by the user.  The rate at 
which the loads are cycled on and off can be adjusted using the parameter 
postMidPointCrossingDelayForAF_cycles.