There are 4 distinct operating area's which build up in complexity. All can be operated manually if required.

Staring with the simplest.

 

Engine shed to fuelling point.

A simple timer cuircit, using a 555 timer to operate a DPCO relay  reverses the polarity.  There is a diode controlled stop section at each end. A diode is a simple electronic component that will conduct in one direction only. Hence it will allow the engine to reverse out of section but not to proceed further in.

 

Shunting the loading bay.

The same basic system but with a point changed every time the loco visits the head shunt. This is achieved using an LDR ( light dependant resistor ), buried in the track bed, to detect when something is above it (blocking the light). For this to work well the level of lighting has to

be consistent. A Picaxe microprocessor is used, over the top for this but was split off one of the others to make fault finding easier.

Another refinement is the use of micro switches, operated by the buffers, to switch in the diode stop in the factory & the siding. This ensures wagons are always shunted to the end of the siding. The springing must be soft enough that the loco's will operate the switch but firm enough to push away the wagons when the loco reverses out. The couplings used are magnetically operated by permanent magnets. Over a series of movements the 2 wagons will be switched about with 1 or both present in the siding, or the loading dock at different times.

 

Shunting the warehouses.

This is more complicated again. This time there are 2 points being changed & which one change depends on where the wagons are.

 Five LDR's  track how the wagons are positioned. The diode stops are again switched using 1 buffer stop & 3 vertical pins in the trackbed which are operated by the axles (not as intrusive as it may sound).

The logic is implemented using a Picaxe microprocessor. These are aimed at the education market & need no special equipment to 'blow', or program, them a windows pc is all that is needed.

The  couplings are magnetic, operated bu permanent magnets. Three wagons are switched round between the siding, behind the boiler house or in front of the warehouse.

 

The circuit.

Each train in the 4 road storage yard has it's own controller so the speed & direction is individually set for each train.

When the route is set the appropriate controller is switched to the track.

Two LDR's detect the arrival / departure of trains from the fiddle yard.

It has a semi manual mode where each ariving train is automatically stopped and the operator has to select the next train & 'dispatch' it.

In fully automatic mode once a train has arived  eaither a timer (adjustable) will dispatch the next train or the operator can dispatch the next train sooner.. The number of fiddle yard roads in use can be restricted ( in case I run out of working loco's) again all controlled through a Picaxe Microprocessor again.