The Digital Model Train Part 3

14 THE DIGITAL MODEL TRAIN PART 3 by T. VVigmore In Part 2 we described the background and design of a locomotive decoder and a two-rail adaptor. This month"s instalment is dedicated primarily to the construction of those units, but it will also describe a modification to the decoder involving a different decoder chip. As we have seen last month, the decoder is designed in surface mount technology (SMT). It is, however, impossible to ob- tain all components as SMT types. Some ICs, for instance, depend for cooling on their housing and if this becomes too small, a heat sink has to be used, defeating the object of the exercise. Therefore, the decoder is a hybrid cir- cuit. It uses a double-sided PCB that is populated at one side with conventional components and at the other with SMT components. Soldering surface-mount components Working with surface-mount (SMT) components requires rather more dex- terity, patience and accuracy than work- ing with conventional components. SMT componen...