Detectors A Short Track Break - with Opto output

This Spot Detector for a DC powered track will be activated when a locomotive wheel set is bridging between the isolated track and the powered rail.

The DC Track voltage will be between 2.8 volts and 12 volts, plus or minus, depending on the motor speed and direction. It may be a constant voltage or pulsing from 0 volts to 12 or higher (some pulsed or PWM throttles can go higher than the 12 volts that the Construction motors are specified for). A small square of strip board or detector such as a silicon diode, transistor or Darlington pair. With current flow in LED it shines on the Transistor which conducts and connects the two output pins. 4N25 Optical Coupler This activates the optical coupler and the 'output' is connected to the 'Gnd' (ground) internally. This grounded connection can then be used by following low power circuits. vero board, 14 holes by 5 can be The circuit is quite simple. As the train used to hold the components. The wheels make contact between the bridge Rectifier type W04 (round) isolated track and the main track a is mounted in 4 holes and will circuit is completed and the track need the holes enlarging to 1.2 voltage is supplied to the rectifier. The mm (#56). voltage, rectified by the bridge, On the diagram the light holes and produces a DC voltage. bars are the copper clad tracks The Optical Coupler contains underside. The dark holes are both an infrared LED and a photo where the which run horizontally on the

components and connecting wires are soldered and the 'X' marks where the copper is cut from around the hole to break the track circuit. The components sit on the topside.

The cuts on the copper side are in column 10 and at rows 1, 2, 3 and 5. Twist a 1/8" (#31) drill bit in the hole to shave off the copper and

leave a break in the strip. 0 ma is the maximum current output If more current is needed then a transistor or a relay should be added. But the output is a pulse or series of pulses as the train passes the spot.

DCC

This Spot Detector for a DCC powered track will get a constantly alternating voltage when a locomotive wheel set is bridging between the isolated track and the powered rail. This Note: for a DC detector the low

voltage will be between 12 and 16 volts. It is rectified by the bridge rectifier to produce a nearly constant DC voltage which through the 1000 Ohm resistor activates the LED in the Optical Coupler and connects the ‘out’ line to the 0 volt or Ground potential.

Installation

Make a small isolated track section. It need be no more than two sleepers long - see appendix also. First solder a dropper wire to the outside of the rail flange of the rails on both sides. Spread some epoxy over the rail flange and around the sleepers where you will cut, to stabilize them. Cut through the track on one rail in two places down to the plastic base. A Dremel cut off wheel is the best, but if you use a small saw then protect the opposite rail with a piece of metal sheet over it. Try and keep the plastic intact and the track section height in line with the powered track. Which track is isolated does not matter. Run wires from the droppers

Components

Resistor

330 ohm or 1,000 Ohms. Which Other items: one depends on the A Bridge Rectifier type W04 power source (round) An Optical Coupler, Capacitor type 4N25, 4N35 or similar. 100 ufd at 6.3 volts for the DC Strip Board 14 by 5 rows. circuit to the input on the PCB.

Take the 'Out' and 'Gnd' from the PCB to the next circuit. Remember it will only be a short trigger pulse present while the speed voltage may not be enough to power a 4N25 Optical coupler so a 4N35 type should be substituted. wheels are on the track section.

Solder on the droppers and fill around the sleepers with epoxy to stabilize them.. 2 cuts are then made with a Dremel cut off wheel. The gap is filled with styrene to prevent shorts. The rails should remain at the same height.

On new track cuts can be made from the bottom up to the rail head, but not through it. Gaps are filled with styrene. When the track is laid then epoxy around the sleepers and use a razor saw to cut through the rail head.