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Thread: New to Model Trains. Looking for advice.

  1. Default New to Model Trains. Looking for advice.

    Hi there everyone that bothers to read this.

    This is my first post and I have a feeling not my last. Im a long time rail fan and I just picked up a HO scale Atlas Model Railroad set for my 5 year old son. Now I know your thinking 5 is to young for a set of this level. But hes not going to have his hands actually on the trains ever. He has CP and a plethora of other medical issues / problems and very poor motor skills.

    Ok to the point of why I set up a account on this forum. Here is what I am dealing with and need help with.

    Becuase he has such poor control of his hinds. I need use a device for him to make the trains move. I have the power supply that came with the set. Its a standard single 0 to 10 dial. I need to some how convert the dial control into a button. To activate to train into motion.

    I have a few potential options.

    I can use a device like the one below. I plug the trains power source into, and then plug a switch into it. The switch is then acting as the dial.
    Below is an image of the type of switch and a type of relay system that I have now to work with. But im worried about damaging the motor of the engine train.

    This is a type of switch that might be used. It plugs in to the device below it.

    This is the device I will have pluged into the wall socket.
    From this device below I would then plug the power supply.

    When my son press's the button it opens the circut.

    But the problem im faceing is. How can I make a control, that will allow him to press or hold down that will slowly bring the train up to speed? I know I cant just leave the power supply set at say 3? So every time he hit the switch the train will move. Or can I with out running the risk of cooking the motor on the train?

    Im am hopping this thread terns into a large discussion.
    If anyone has any ideas? Or question about what im trying to do or say? Please unleash your thoughts. I have 24 days until xmas to have this figured out.
    Last edited by Rustolum; 12-01-2009 at 04:14 PM. Reason: spelling

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    Here is a image I made up quick to help explain what I have at this point to work with at this point.
    Last edited by Rustolum; 12-01-2009 at 04:15 PM.

  3. #3


    First, let me express my admiration for you trying to help your son overcome his disabilities and enjoy the fun of running trains. You've come up with some really interesting issues. If I understand you correctly, you'd like him to be able to press a button and, as long as he keeps pressing it, the train will continue to accelerate. If the button isn't held down, the train will continue to run at the set speed. If he presses and holds the button again, the train will decelerate, eventually coming to a stop. Do I have it right so far? If so, we'll have to come up with an additional button that will act as an emergency stop, cutting power to the tracks, since you'll run into situations where you need to hit the brakes immediately.

    You can leave the power set at something like three but, every time he hits the button, the train will take off like a jackrabbit. It won't hurt the engine but it won't look very good and you'll have a much better chance of derailing a car or cars because of the fast slack action on the couplers. This also still leaves us with the emergency stop issue.

    My first thought would be to adapt a remote control dimmer switch like the one at It's inexpensive and operates as an up and down switch just by pressing the top or bottom of the button. It will retain the voltage setting when turned off, this providing us with the cruise control function. All you'll have to do is plug the power pack into the receiving device, open the throttle to full, and then he could control the power to the power pack by pressing the button up to gradually increase speed or down to gradually decrease speed. Do you think the concept of a two way button press would work? I'm thinking of painting the top of the button green for faster and the bottom red for slower. If you think he can distinguish between the two ways to press the button, this may be a good solution. I still need to ponder how to add an emergency stop. Let me talk to my brother tonight, who's an electrical engineer, and see if we can come up with some more ideas.
    Last edited by UP2CSX; 12-01-2009 at 05:05 PM.
    Regards, Jim
    HO Scale Modeler

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    Don't know how good/comfortable you are soldering circuits, but the need for a single button to control several functions makes me think micro controller.
    Do you think the concept of a two way button press would work? I'm thinking of painting the top of the button green for faster and the bottom red for slower. If you think he can distinguish between the two ways to press the button, this may be a good solution. I still need to ponder how to add an emergency stop
    I agree fully with what UP2CSX said. A button with a top and bottom seems like a good idea. I don't know how much you know about electrical engineering, so this long explanation may not be necessary, but here it goes.

    Pulse Width Modulation is a means of controlling the motion of a motor by sending pulses of electricity at full power to the motor for a specific amount of time. The speed at which the motor runs depends on the voltage at the motor. By using pulses, the voltage the motor sees varies with time. The longer the pulse, the higher the voltage the motor sees. I will not explain the physics behind this phenomenon as a google search of PWM will give many resources on the subject.
    An H-bridge is a device that takes the low level signals from a 5 volt PWM signal and steps them up to 16 volt power you would use for the track. It has two input lines. The input line that is pulsed controls the direction of the motor (and thus the direction of the train). In this case, I get the feeling that the train will be traveling in only one direction. If this is the case, you could use a single Darlington transistor to step up the voltage instead of an expensive H-bridge. A transistor in general is a device with three line in it. Two lines act as a giant resistor (no electricity is allowed to flow) . The third line is a control line called the base. When the base is powered, electricity is allowed to flow between the other two pins. A transistor is an amplifying device because 16 volts can be applied across the resistor part and the base can be pulsed with the 5 volt signal of a microcontroller. A Darlington transistor is simply a transistor that can handle more than about 300 miliaperes of current across it. You will need one. They can be found at some radio shacks, though not as many as you use to be able to. I recommend either or for parts.
    The next step is to build the interface box for your son. I would use either a PIC microcontroller or an audrino micro. Audrino's are easier to program, but PIC's are much cheaper. If you go with a PIC, make sure the controller has at least three interrupt pins. Interrupts will allow the controller to know when a button is pressed. Here is a link that has some good programing information.
    Programing organization
    A microcontroller will run a continous loop of code. The main part of its code will be controlling the motor. It will have a variable in its memory. This variable will hold the speed of the train. One control line will send out pulses continuously whose duration based on this variable. These pulses are the PWM signal discussed earlier. In the code there is an place called an interrupt. When a button is pressed, the micontroller automatically jumps to this portion of the code. It will increment/decrement/0 the speed variable according to which button was pressed and then return to what it was doing last. I am not the best PIC programmer and am having a little trouble coming up with a way to deal with a held button. Maybe someone a little more knowledgeable than me can help if he decides to go this route. If you want to use an h-bridge it complicates things a little more, but not much.
    Let me know if you want to do this or want more information/diagrams

    good luck

  5. #5


    I talked to my brother tonight and he sees no reason why the lamp dimmer I linked to wouldn't work for a straight DC power pack, since the speed of the train varies directly with the voltage. The lamp dimmer is just another form of rheostat that's already in the power pack. He had a great idea for the emergency stop issue. Just buy a Clapper! Plug the power pack into the Clapper and then plug remote receiver into the Clapper, either directly or using a power strip for the powerpack and the remote receiver, with the Clapper between the power strip plug and the wall outlet. As long as you or your son can clap your hands, you get an immediate power shutdown of the whole shebang, and the train will stop. Seems like you could do the whole thing for about $60, especially if you can get the Clapper on sale at Walgreens for $10.
    Last edited by UP2CSX; 12-01-2009 at 10:35 PM.
    Regards, Jim
    HO Scale Modeler

  6. Default

    I too first thought of two buttons. One to speed up and one for speed down. A memory light dimmer is a great, simple, and cheap solution. My brain had spun off to more complex things liek transistor throttle with electronic ladder-latches for the speed control.

    Buy the way I had HO scale trains when I was 4 or 5. I've never understood the argument that HO is too small/fragile etc. for children of that age.

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    Rustolum, im only 14 but my dads an electrician and he"ll be home from work in about 2 hours or so, when he gets home and settled ill show him the thread and see what he can do for you. best of luck to you with your son and modeling trains

  8. Default

    Ok I thought about it for a few minutes and an electronic throttle with two buttons is easier than I originally thought. I don't need no stinking latches. Simple actually.

    I just threw this together in a few minutes so I haven't thought about or prepared specifications for all the parts but in general:
    Q1 is the control transistor
    Q2 is the power transistor
    C1 is the main capacitor that really controlls the train speed. Something like 250MFD. Too large and it will be too hard to control. Too small and the train control will be jerky.
    R1 controls how much the train decelerates each time the button is pressed or how fast it decelerates if held down. A value of under 10 ohms would be an immediate stop unless C1 is enormous.
    R2 controls how much the train accelerates per button press. The train will slowly come up to speed when this button is pressed and held.
    R3 is a bias to match Q2 and keep the train from creeping away.

    There are many other things that could be added to make it better, but the concept of two buttons was there.

    Another thought is that one could just have the accelerate button. Let the train automatically slow down when the button is not pressed. That would have the side benefit of always eventually stopping the train.
    Last edited by Western Star; 12-02-2009 at 01:35 PM. Reason: correct link & spelling

  9. #9


    WS, that's a good design too. One reason I favor the lamp dimmer is that it's wireless, so the boy doesn't have to worry about getting tangled up in any wires. I also like the the idea you can turn it off an let the train run at the same speed, whcih might be a good safety measure if he has a tendenancy to what I did as a kid - run it as fast as I could to see how far it would fly off the tracks. The other good thing about the light dimmer is it's already built and takes no electrical knowledge to hook up except to plug it in.
    Regards, Jim
    HO Scale Modeler

  10. Default

    Maybe my microcontroller throttle was a little overdone. I am studying to be an electrical engineer so simple is not on my mind at the moment. I like Western Star's idea much better. Simple, durable, easy to build. Great Idea.

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