Component list is as follows:-

PIC 12F629
78L05 	regulator
L272 	dual power op-amp
R1,R2   10K 1%
R3,R4   1K 1%
R13,R14	10K
R15	4R7 0.25W (use a higher power resistor e.g. 2W if it gets too hot!)
C1    	1uF 35V (or larger if possible) electrolytic/tantalum
C2,C4   100nF ceramic
C3	470nF ceramic
D1,D2	1N4148
D4-D7	UF4001 or UF4003
D3	27V zener diode such as BZY89C27 or 1N971B


I have not included provision for back up power (as in Lenz PS1) because I
think it complicates things. The 1% resistors are specified to allow the
processor to decode packets even if the track voltage drops to virtually
nothing for a short while (for instance during a momentary short circuit or
if a wheel goes over some dirt). The worse the tolerance of the resistors
the greater the effect of the intrinsic (non adjustable) voltage offset in
the on board comparator of the PIC. The circuit will work pretty well with
higher tolerance resistors, but better with lower tolerance ones.

New Features in V1.02
---------------------

Added circuit R14,D2,C4 to ensure that track signal appearing at the PIC is
between oV and 5V. This should allow the circuit to work with track voltage
down to well below 1.2V for a short while.


New Features in V1.03
---------------------

Corrected value of R3 and R4 from 2K7 to 2K2 to allow operation up to at
least 24V on the track

New Features in V1.04
---------------------

Added over voltage protection components to prevent component failure if
the peak track voltage exceeds 35V. This should ensure compatibility with
the Hornby Select.

New features in V1.05
---------------------

Adjusted values of R3 and R4 from 2K2 to 1K to allow better decoding performance at higher track voltages and to allow the use of 3.3V regulators instead of the 78L05 for better DC performance.
Changed the value of D4-D7 to allow the total decoder output to exceed 300mA.
Changed the value and rating of R15 to match that supplied in the kits.
Added the part numbers of the zener diodes supplied in the kits.
