Protector

Description: The circuits presented here will prevent turnouts from being thrown while a train is on a switch, which is ideal in situations where the switch cannot be seen by the operator. They utilize phototransistor sensors to detect the presence of a train and incorporate a short time delay to account for gaps between train cars. The circuit can also be adapted for use with crossovers and ladder tracks by adding more sensors. There are two versions of the circuit: the first employs push buttons and is designed for twin-coil switch machines, while the second utilizes a toggle switch and can be modified for other types of switch machines. The primary distinction between the two versions is that the second version includes a memory function that allows for delayed activation of the turnout until the train has cleared the switch. The push button version of the protection circuit disconnects the switch machine from its power source whenever a train is detected on the switch. This version is suitable for twin-coil type machines. When the voltage across the capacitor reaches half of the supply voltage, the output of IC 1b will go high, deactivating the relay. The time required for the capacitor to charge to this voltage is approximately 6 to 8 seconds. This protection circuit replaces the mechanical relay with a Silicon Controlled Rectifier (SCR), facilitating easier PCB construction and potentially reducing costs. The advantage of using a relay instead of an SCR is that the switch machines will continue to operate even if the protection circuit loses power or fails. When no current flows through the optoisolator's LED, its output transistor remains off, preventing the SCR from triggering. When either push button is activated, no current flows to the coils since the SCR cannot turn on. When the capacitor charges to half of the supply voltage, the output of IC 1b will go low, activating the optoisolator and enabling the SCR to be triggered. The toggle switch version of the protection circuit incorporates a flip-flop memory circuit and a relay between S1 and the switch machine. The flip-flop retains the last position of the turnout while a train occupies the sensors, preventing it from being thrown. When the capacitor voltage reaches half of the supply voltage, the output of IC 1b will go low, reconnecting S1 to the circuit common. If S1 has not been moved when the time delay expires, the turnout will remain in its original position. However, if S1 has been changed, the turnout will automatically adjust to the new position. This circuit can also be adapted to control devices other than relays. For example, it could be integrated with another system using an optoisolator or a solid-state relay. The phototransistors may be replaced with inputs from a block detection system, ensuring that the switch remains protected while the block is occupied by a train. Turnout position indicator lights are essential with this type of system, as they provide the only means of determining the current alignment of the track.

The described circuit implements a safety mechanism designed to enhance operational efficiency and safety in model railway systems. By utilizing phototransistor sensors, the system can accurately detect the presence of a train on a switch, thereby preventing potentially dangerous situations where a turnout may be thrown while a train is still occupying the switch area.

The push button version of the circuit allows for straightforward integration with twin-coil switch machines. It employs a simple logic where the activation of a train sensor results in the immediate disconnection of power to the switch machine, thus preventing any unintended movement. The use of an SCR instead of a mechanical relay not only simplifies the PCB layout but also reduces the number of components required, leading to lower production costs. The SCR's ability to remain off until triggered by the optoisolator ensures that the switch machine remains in a safe state when the circuit is inactive.

In contrast, the toggle switch version introduces a more sophisticated memory function. This feature is particularly useful in scenarios where the operator may not be able to monitor the switch directly. By retaining the last known position of the turnout, the system ensures that the turnout will not change until it is safe to do so. This is facilitated by the flip-flop memory circuit, which keeps track of the switch's state while the sensors are occupied by a train.

The adaptability of these circuits allows for integration with various types of switch machines and operational setups. The potential to utilize inputs from block detection systems further enhances the system's functionality, ensuring that the switch remains protected during train occupancy. Additionally, the incorporation of indicator lights provides critical visual feedback to operators, allowing them to ascertain the current state of the track alignment at a glance. Overall, this protection circuit represents a significant advancement in the automation and safety of model railway operations.The circuits presented here will prevent turnouts from being thrown while a train is on a switch, ideal where the switch cannot be seen by the operator. They use phototransistor sensors to detect the train and have a short time delay to compensate for gaps between cars.

The circuit can also be used to protect crossovers and ladder tracks with the addition of more sensors. There are two versions, the first uses push buttons and is for twin coil switch machines. The second uses a toggle switch and can be adapted for other types. The main difference between the circuits is that the second version contains a `memory` function that will allow delayed throwing of the turnout until after the train has cleared the switch. The Push Button version of the protection circuit simply disconnects the switch machine from its power source when ever a train is on the switch.

This circuit could be used for Twin Coil type machines When the voltage across the capacitor reaches 1/2 of the supply voltage the output of IC 1b will go HIGH and the relay will be turned off. (The time required to charge the capacitor to this voltage is 6 to 8 seconds. ) This version of the protection circuit replaces the mechanical relay with an SCR, (Silicon Controlled Rectifier).

The SCR will allow easier `PCB` construction of the circuit and may be cheaper to build as well. The advantage of using a relay versus an SCR for the output is that the switch machines will still operate if the protection circuit has no power or fails. When no current is flowing through the optoisolator`s LED its output transistor will not conduct and the gate of the SCR will not be able to trigger.

When either of the push buttons is activated no current will flow to the coils because the SCR cannot turn on. When the voltage across the capacitor reaches 1/2 of the supply voltage the output of IC 1b will go LOW, the optoisolator will be turned on and the SCR can be triggered.

(The time required to charge the capacitor to this voltage is 6 to 8 seconds. ) The Toggle Switch version of the protection circuit places a flip flop type of memory circuit and a relay between S1 and the switch machine. The flip flop will remember the last position of the turnout while the sensors are covered by a train and prevent it from being thrown.

When the voltage across the capacitor reaches 1/2 of the supply voltage the output of IC 1b will go LOW and S1 will again be connected to the circuit common. (The time required to charge the capacitor to this voltage is 6 to 8 seconds. ) If S1 has not been moved when the time delay is runs out the turnout will stay in its original position.

If however S1 has been changed the turnout will automatically change to the new position. The circuit could also be adapted to drive devices other than relays. The protection circuit could for example be tied into another system with an optoisolator or a solid state relay. The phototransistors could be replaced with an input from a block detection system. The switch would then be protected while the block is occupied by a train. Turnout position indicator lights are a must with this type of system as they are the only way to know which way the track is actually lined-up at any given time.