Speed Control

Electronics let trains run smoothly...

This is in essence a switched power supply, a pulse-pause power generator. This gives an advantage when controlling little DC-engines: lower speeds are possible. For the block-secured main track, this regulator receives two digital inputs (D0, D1), so four speeds can be generated: full, slowed, very slow and stop. On other tracks, it can be regulated using a classic potentiometer. Acceleration- and breaking-speeds are adjustable.

Left the schematic of the speed controller, right some built power amplifiers:

At the clock-input a triangular signal, 75Hz, arrives, generated by a 555-timer and a 741 op-amp (not drawn here). This generator provides all speed controllers with a simultaneous "heartbeat". This signal is then compared to the voltage level, coming from the transistor-switched digital inputs. The condenser and trimmers slow this reference voltage down. The output is amplified by two transistors and secured by a 21-Watt car light bulb. The resistor at the output is placed to have reliable occupation detection, even when the speed controller stops the train.
48 of these controllers are built so far: one for each part of main track. One circuit board contains four of these controllers. The power transistors are mounted in-group on large cooling plates.