Detail for my remote_Mk2_receiver_1b.ino sketch

This sketch is for use as the receiver part of a Mk2 PV Router system 
that is operated via an RF link rather than via a control cable. It is 
intended for use with my PCB-based hardware.
 
One current sensor is supported at the CT2 port.  This can be used for
monitoring the power that is diverted by the receiver unit. The 
diverted energy total in kWh is available at the 4-digit display connector.  
The display returns to its idle state after a period of 10 hours during 
which the control signal has never been in the 'on' state.

The CT1 port has been re-allocated for driving a pair of LEDs to show 
the status of the RF control link. The circuit for this feature is shown
in the header of the sketch.

The output signal for controlling the load, as instructed by the 
associated transmitter, is available at the "mode" port (D3) in active-high 
format and at the "trigger" port (D4) in active-low format.

The corresponding transmitter sketch is: Mk2_withRemoteLoad_n.ino 

Changes for version _1a:
- A minor change has been made to the function timerIsr() so as to resolve
a timing anomaly that has previously existed.  With the new arrangement, a 
complete set of data samples is made available by the ISR for use by the
main code.  There is no longer any possibility of these values being 
overwritten before they are processed.

- the display timeout period has been reduced to 8 hours instead of 10.

Changes for version _1b:
- The variables to store ADC data are now declared as "volatile" to remove 
any possibility of incorrect operation due to optimisation by the compiler.