Automatic Automatic Turnout and Reverse Loop controller

Chapter-4a Page 17

Automatic Turnout Operation

Sometimes it happens !

A sudden stop and perhaps an alarm sounds and you've done it again! forgotten to set the turnout.

Maybe it is out of sight or poorly situated and not obviously set the way it should be. Of course a 2 aspect ground signal would be an advantage, but better still would be automatic operation of the turnout. This circuit will show how to overcome the problem if you use Circuitron Tortoise motors. Originally designed for DC but it can be modified for DCC operation as well.

The block diagram:

On the red colored track there are two spots where the train will be sensed as it moves toward the turnout. When a train enters at (A) it will be detected passing the 'spot loop'. If the turnout is set for the Main then it will be transferred to the Loop side. A timer is started and the track power removed.

On timeout the power is restored and the train proceeds. The time is long enough for the Tortoise motor to transfer the turnout. If the turnout is set correctly then the train does not stop. Also shown is the frog power connection which is supplied by the other changeover contacts in the Tortoise. Optional manual control is by a momentary contact toggle switch (ON-OFF-ON type).

Installation:

There is an edge connector plug available for the Circuitron Tortoise motor. This may be more convenient than soldering on wires under the layout. The numbers in the schematic refer to those on the motor. The plug is double sided and if the motor is not working in the correct sense i.e. select main and you get the loop, then the plug only needs to be turned round and reinserted to get correct operation. The switch connections will still be correct as the reversing of the motor will change them over. If the turnout changes in the wrong direction but is correct when using the manual switch then the connections to the tortoise switch need to be swapped over. The position of the spot rails will need to be determined on the layout. They must to be far enough from the turnout so that the train has room to slow down plus a bit more. The controlled track section (from 'A' to the spot) must be long enough to hold all MU'd locos. For detail on making the spot rails see the appendix. The 100 ohm resistors are installed as shown in the track connection diagram.

Construction:

Cut the vero board to size. Thirtysoldered direct or solder lugs three holes along the copper buss can be used. If you use plug and 20 holes high. Clean the copper connections run jumper wires to and mark on the copper side the the original positions. positions of the cuts - 'X' on the When finished check all diagram. Double check each one solder joints with a magnifier. before you make the cut. Twist a 1/8 Run a craft knife blade along the inch (#31) drill in the hole to remove insulation strip between the the copper from around it. Remove copper strips any small copper daggs that still remain and burnish the copper to flatten it again. Check with a magnifier or meter that the copper is gone and no circuit exists across the holes.

Install the 20 link wires. Use a small diameter single strand, insulated copper wire, such as Kynar 'Wire Wrap' wire. Note that there are some links to install under other components (shown in red), these can be bared wire to reduce the height. Next install the 7 resistors and 4 diodes, observe that the banded ends are correctly placed. The rest of the components can now be installed. Some holes have to be drilled out to 1.2mm (#56) for the larger leads. The PCB connections can be - If it snags there may be a solder short between the two strips. Meter again across the cut copper holes for any solder bridging them and also meter between the +12 and 0 volt pins for possible short circuits.

Schematic:

The circuit is in three parts. The two spot detectors that sense the train passing are optically coupled to the LM556 which is the Tortoise driver and to a relay to remove track power while the turnout motor is changing. The LM556 is a dual timer that houses two LM555 chips. These are not used as timers but are set to

NOTE: for DCC operation the 390 ohm resistors (390R) at the bridge rectifiers should be 1,200 ohm (1k2) and the OPTO's changed to type 4N25, the 100ufds caps changed to 10ufd electrolytics. either on or off to supply the power to The output from the spot the tortoise motor. The sense circuit detector also activates the relay is connected to the opposite points driver, a 2N4403 or 2N2907 position switch in the Tortoise. This transistor, to pick the relay. This means that the train can come in will remove the track power through the main or straight through feed. A capacitor discharge time point and not change the turnout delay holds the relay on until the when it crosses the spot detector on turnout has changed. There is that track. an un-committed 'low' going The spot's 'opto 4N35' output to the output from the tortoise driver LM556 is a 'low' level and this is (pin 1) that could be used for presented to the reset signaling or for other uses. input of one of the timers and the Two sets of relay contacts are trigger input of the other to generate available so that loop and main the correct voltages for the Tortoise tracks can be on different motor. blocks. A 100 ohm resistor must also be included on the terminal blocks (as shown) which causes the loco to slow to a stop and also makes the stopped train still visible to a block detector. This resistor can be changed if not effective. Increase the value if the loco continues to run on and into the turnout. Manual operation of the points is by a momentary contact (Center

off) switch.

Resistor Color Codes:

The tolerance band will be Gold for 5% and Brown for 1% resistors Symbol Value Number. 3 band plus tolerance. | 4 band plus tolerance band. 390R 390 Ohms 2 orange-white-brown | orange-white-black-black 1K2 1,200 Ohms 1 brown-red-red | brown-red-black-brown 33K 33,000 Ohms 1 three orange bands | orange-orange-black-red 47K 47,000 Ohms 3 yellow-violet-orange | yellow-violet-black-red 1M0 1,000,000 Ohms 2 brown-black-green | brown-black-black-yellow problem if a motor change or

Components

Resistors, 1 of 47,000 Ohms, [47K] 1 of 1megohm, [1M0] 2 of 33,000 Ohms, [33K] 1 of 1,200 Ohms, [1K2] 2 of 390 ohms [390R]

1 2N4403 or 2N2907 PNP transistor 1 of 1N4004 diode 3 of 1N4148 diodes 1 of LM556 dual timer IC 2 of 4N35 optical couplers 2 of W04 bridge rectifier Capacitors, 1 of 0.01 ufd, [0,01u] 1 of 0.1 ufd styrene [0.1u] 1 of 1.0 ufd, [1.0u] Electrolytics, 1 of 33ufd at 16 volt working 2 of 100ufd at 16 volt working

Relay DPDT 12volt 10amp A 33 hole by 20 hole strip board PCB headers or screw terminals for board connection if wanted

Tortoise slow motion machines

are fairly universal. Designed To be connected with a plug. Many are used with the wires directly soldered on - this is a 2 of 3 way PCB screw terminals

shift to another location is required. The correct plug is available from Circuitron.com