model railroad controller circuit

Model Railroad Controller with Presence Detector

model railroad train Railroads are a big part of the history. They take us back to an earlier time where once trains were the fastest way to cross a huge land. Model Railroading could take you back to those more good old times, and it is a greatest hobby. Probably,you have already noticed that this will be one of the most rewarding and relaxing hobby that you will ever experience. Model train shows are very common, and you can watch the excitement of visitors when their eyes glued to the moving locos. Perhaps, you are now busy with the set up process of your own model railroad show!

Okay, when you prepare your railroad layout for a public event you may not want the train to run continuously but only when someone is there to enjoy it. This simple “Model Railroad Controller” circuit activates the train on a loop of track so that it goes around for a finite time when a visitor is approching, and always returns to the departing point where it waits patiently for the next visitor.

In this simplest method, a slight modification in the existing track wiring is necessary as indicated in the track layout shown below. Here, the train power is always connected to the main loop,but the stop block (departing point) is normally unpowered, and controlled by the railroad controller electronics.


Hope you start with a pre-packaged train set. The starter set almost always include a power supply along with the track and train. Most two-rail track systems use DC (Direct Current); one rail is positive, the other is negative (ground). The power supply polarities can be reversed to change the direction of the train. Make sure you are getting the right type of power supply for your layout. Connect the railroad power supply unit to your modified track as shown here.


What’s next? Just follow the schematic circuit diagram to build your own model railroad controller unit (which is nothing but a “LASER Beam Trip Sensor” based visitor detector), and connect the finished circuit to port J1. You can use the existing railroad power unit or an independent power source to energize the controller block.


In case of a visitor detection, the controller will apply power to the stop block and the train will move. The controller circuit also ensures (with the help of the relay contacts) that the stop block remains in the power-up state until the train exits the stop block (otherwise the train may not move enough to pick up power beyond the isolated track), and the stop block is in power-down mode thereafter. For this second task, an ordinary reed switch (N/O type) lies between the tracks is connected to the main controller circuit. When the train passes over the reed switch a magnet that is pasted at the bottom of its frame activates the reed switch and this toggles the controller circuit to remove power from the stop block.

model railroad controller circuit

When it comes to an exhibition hall, LASER triggering is more precise than a PIR sensor. The laser is pointed at an LDR (Cds cell) and when the beam is broken, the electro-magnetic relay activates and stays activated as long as the beam is broken. The laser card/head module can be located at probably greater than 20 feet from the LDR and will work in fairly bright ambient light. Compact LASER card / HEAD (5VDC) modules are now widely available; thanks to Sparkfun, DX and eBay!


Note: The explanations for the circuit presented here cannot hope to cover every situation on every layout. For this reason be prepared to do some experimenting to get the results you want. The true inspiration for this project was derived from a future advanced project the designer intend to build in near future!

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