Electric lock switch

Controller circuit for an electric lock switch

This project is a controller for an Electric Lock switch widely in operation throughout the world. While it forms an integral part of signaling, this implementation tries to avoid any direct connection to signaling equipment like APB intermediate signal controllers, still providing the protection needed by an open turnout.

The turnout itself is manually controlled by a switch rod. See Bernd Schneider's description, and for non-German speaking people, the images show the idea, I think. This switch rod activates a miniatur toggle switch that controls frog polarity, additionaly to securing the turnout in the desired position. A second pair of contacts allows for turnout position feedback.
A horizontal hole in the rod (this and following is not shown on the above website!) allows a metal locking bar to slide in and out when the switch is normal (closed) and to lock the rod. An inserted locking bar will safely prevent personnel from throwing the switch.

The locking bar is electrically activated by a modified switch machine, also providing position feedback. I plan to use a Tortoise and Rob Paisley's OpAmp Stall Motor switch machine driver with 5V TTL input, but that is not yet decided. Two push buttons allow the user to request locking and unlocking of the switch.

An infrared proximity sensor mounted a short distance from the switch points serves as track circuit. But most important, when the switch is open a resistor bridges the rails carrying DCC power, simulating occupancy and causing the signals protecting the block to fall to red. The resistor is cut in with a relais.

So how is the Electric Lock switch operated?
After having pushed the 'Unlock' button, the resistor relais is immediately activated and signals will fall to red. The device will only unlock after a timeout of 20 seconds (5 scale minutes in N), or immediately, if the track circuit is occupied. The lock motor will then pull the locking bar out of the switch rod, so that the turnout can be thrown. When the switch is closed (normal) again, and the pushbutton 'Lock' is activated, the locking bar will be reinserted. Locking is only possible if the switch is normal, this explains the need for the switch position feedback.

The switch position feedback must be wired in such a way that a closed/normal turnout closes the contact and pin 15 is at High level. In analogy, a correctly inserted locking bar closes the feedback switch and causes pin 17 to be at High level.

The power circuit takes input from whatever source you like, for example from an APB feeder line. Hooking it up to the nearby track will not work, as the current draw would cause occupancy on the line. The switch machine for the locking bar is fed 9 V, and the rest of the circuit gets its power through a 7805 linear tension regulator.
The switch machine control circuit is not shown, please refer to Rob Paisley's site (link is above).

Documentation and Source Code

Schematics

Version 0.9 [download]
Please substitute the 1N4007 diode with a 1N4148.


Source code

Version 0.9a [download]