Proportional-Integral-Differential Train Controller with Autostop

I discovered the power available in PIC microcontrollers recently, and have spent a couple of months of late nights applying them to train control. The PCB at right is the finished prototype of the first model I designed.

The design has a full User Manual (pdf, optimised for printing) that explains its operation in more detail.

This type of train control has a number of advantages:

It controls speed of a locomotive very precisely, better even than proportional feedback controllers such as the Gaugemaster or my analog designs;
Low cost and lower complexity than the analog versions;
Simulated inertia as well as feedback;
Inertia can be adjusted or switched off;
Automatic station stops in response to button press or signal from track;
Indicates conditions such as halting, overload or timeout;
Times out to stop a train that has inadvertently been left running;
Control constants can be user-changed to suit different scales (rather than being fixed at build).

This is a picture of the prototype in a walk-around format. The red LED indicates power applied, the green one the track power, and the yellow LED is the processor signal LED. The reverse switch is visible at the top of the box.

The PCB layout is shown at right and the circuit diagram is below.