This is one of my personal electronic projects and its current state is work in progress.

Model Railroad Speed Control

This project is about a model trail speed control circuit designed by Juergen Kuehnel of Analog Devices. The circuit uses back-EMF from the train engine motor to determine the current speed. This circuit has the characteristic that the engine will go a constant speed irrespective of up/down grade. One nice thing about this circuit is the low speed operation.

The circuit emits a fixed width pulse and varies the height of the pulse to vary engine speed. (In-other-words, it is pulse height modulated rather than pulse width modulated.) The duty cycle of the pulses is about 90% with the 10% "off" cycle used to measure the back EMF from the motor to complete the feedback loop.

The current state of this project as of 1998-03-15 is that the Rev. B version of the circuit board has been fabricated, stuffed and tested by Juergen. There were numerious little problems, but eventually Juergen got both boards to work with some trace modifications. We hope to fix all of these problems with the new and improved Rev. C version of the circuit board. In addition, we hope to reengineer the circuit to use more commonly available components.

By the way, revision A is the hand wired version done by Juergen. There has never been a revision A printed circuit board.

Copyright (c) 1996-98 by Wayne C. Gramlich All rights reserved.