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  • Author Author: colporteur
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Pulse Width Modulation a Speed Equalizer

colporteur

Take advantage of pulse width modulation (PWM) to control the motor of a model train.

This entry for the Project 14 project theme World in Motion documents a project I am currently working on. My hobby is creating animation in model railroad layouts. My passion is writing. I plan to use PWM to control the speed of a train. Let’s couple the delivery of the project with a Project 14 challenge, creating a resource that someone might find of interest.

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The speed and direction of a Direct Control (DC) HO scale model train locomotive is determined by the voltage level and polarity applied to the tracks. The tracks act as the conductor to the locomotive motor. Increasing the voltage, the locomotive goes faster, decreasing the voltage, and the locomotive goes slower. The polarity of the voltage applied to the track sends the locomotive forward or backward.

Pulse width modulation (PWM) is a modulation technique that generates variable-width pulses that can be used to control the amplitude of an analog signal. The average value of the analog signal fed to the load can be controlled by adjusting the pulse width of the signal being delivered to a controller. The controller output is on more of the time for a longer pulse width and off more of the time for a short pulse width.

Follow this design challenge to learn a little about PWM, examine the bill of materials for a practical design application and see the technique in action on an HO scale model train locomotive.

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  • Very nice project idea. Not to get ahead of your ideas, but will the PWM be manually adjusted or are there plans to automate the speed based on position of the train on the track? For example, have the train slow down if a prox switch ( or limit switch or IR detector) identifies the train is in the switchyard or approaching a road crossing ? 

  • in reply to robogary

    I'm just in the process of writing the introduction that would contain some of those details. 

    I am in the process of testing an automation sequence using two trains on individual sidings sharing a loop of track. I am using an Arduino code to move the trains through four stages stop, departure, in-transit, arrival and stop. The stages are determined by sensors that monitor the trains location. Each stage has a motor control dependency. 

    I'm currently with my spouse on holidays. Computer time is when she goes shopping. I only have my laptop so I don't have the drawing to share. 

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  • in reply to robogary

    I'm just in the process of writing the introduction that would contain some of those details. 

    I am in the process of testing an automation sequence using two trains on individual sidings sharing a loop of track. I am using an Arduino code to move the trains through four stages stop, departure, in-transit, arrival and stop. The stages are determined by sensors that monitor the trains location. Each stage has a motor control dependency. 

    I'm currently with my spouse on holidays. Computer time is when she goes shopping. I only have my laptop so I don't have the drawing to share. 

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