Automatic Station Stop Circuit

  The "Automatic Station Stop Circuit" brings a train to a station stop in two braking steps and then sends the train on it's way after a set period of time.

  The first braking step slows the train gradually until it is at the station. The second brake step then stops the train just quickly enough to allow the first or second coach to stop in front of the station.

  After an adjustable interval the train slowly accelerates to continue its trip.

  Also shown on this page is a throttle that could be used with the Automatic Station Stop Circuit. The throttle is designed for continuous automatic operation only. The throttle section could be modified and added to the controls of and existing throttle.

  This circuit is designed to operate as a stand alone unit. That is to say - The train would be on its own loop of track as in an automated display situation.

  The circuit could be modified to operate as part of normal throttle with the addition of some external switches.

  The following diagram shows the placement of the phototransistors along the track and how the braking steps would be carried out.

Automatic Station Stop Sensor Placement

  When the train crosses the first sensor the train starts to slow down. The train should be moving 10 to 20MPH when the engine reaches the second sensor.

  When the engine covers the second sensor the train slows just quickly enough to allow the train to stop with one of the coaches in front of the station.

  The next diagram shows the Automatic Station Stop Circuit's schematic.

  The circuit is built around three comparators and two timers. Phototransistors are used to sense the position of the train and optoisolators control the output of the throttle.

Automatic Station Stop Circuit schematic

1. When phototransistor Q1 is covered by the approaching train the output of IC 1A will go LOW. This causes the output of IC 1B to go LOW and the optoisolator OI 1 is turned ON.

2. The voltage across capacitor C1 in the throttle starts to decrease and the train slows. The rate of this decay is determined by the settings of R2 and R3.

3. When phototransistor Q2 is covered by the approaching train the output of IC 1C (RED line on schematic) will go LOW . This triggers the timers IC 2 and IC 3 and their outputs to go HIGH.

4. When timer IC 2 is triggered optoisolator OI 2 is turned ON and drains capacitor C1 in the throttle at a faster rate causing the train to slow more quickly. The rate of this decay is determined by the setting of R3.

5. When timer IC 3 is triggered its output (BLUE line on schematic) goes HIGH and two functions occur:

   1- The output of IC 1B is forced to a HIGH state. This turns OFF optoisolator OI 1. Also any changes in the output of IC 1A are now ignored.

   2- Pin #2 of the timer IC 2 is held HIGH. This prevents IC 2 from being retriggered by changes in the output of IC 1C while the train is leaving the station.

6. When timer IC 2 resets OI 2 is turned OFF and the voltage across capacitor C1 in the throttle begins to increase and the train will leave the station. The rate of acceleration is determined by the settings of R1, R2, and R3.

7. When the train has left the station and Q2 has been uncovered for approximately 5 seconds timer IC 3 will reset and the circuit will be ready for the next train.

• The values of the 1Megohm resistors in series with the phototransistors might have to be decreased in order to increase their sensitivity if the room lighting is strong.

• Timer IC 2 will reset based on the values of its timing resistor (1Meg variable) and capacitor (33uF). This setting determines how long the train will be stopped at the station.

• Timer IC 3 will cannot reset until Q2 has been uncovered continuously for approximately 5 seconds. This allow the train to completely leave the station without retriggering the circuit.

  Timer IC 3's triggering is delayed by about 1/10th of a second after the output of IC 1C goes low. This allows timer IC 2 to trigger before its pin #2 is forced into a High state.

• The - Automatic Station Stop Circuit - is by design unidirectional. The circuit could operate in both directions with the addition of extra sensors and the necessary switching.

• Phototransistors are used for train position sensing but other methods could be used if desired as long as the inputs to IC 1A and IC 1C can be made to go above 8 volts when a train is detected.

• Some testing may be needed to find the best location for the phototransistor Q2 as this is somewhat dependent on the length of the coaches and engine used.

• The circuit shows the use of two 555 timer chips for explanation purposes but one 556 dual timer would normally be used.

• The reference voltage at the inputs of the comparators is taken from the "control" terminal of timer IC 2 (PIN 5). The control terminal of 555 and 556 timers is internally fixed at 2/3 of the supply voltage.

  This cheat saves the cost of two resistors at the price of a slightly more complicated circuit board.

  The next schematic shows a dedicated throttle that could be used with the Automatic Station Stop Circuit.

  No reverser is shown with the throttle as the circuit is by design unidirectional. The circuit could operate in both directions with the addition of extra sensors and the necessary switching.

Automatic Station Stop Circuit Throttle

• The values given for the potentiometers and capacitor C1 in the the throttle circuit are suggestions only. Some testing might be needed to get the desired results for your particular situation. When setting up the circuit R3 should be set first, then R2 and R1 last.

  - R3 is set so that the train stops with the passenger cars in front of the station.

  - R2 is set so that the train traveling at 10 to 20 MPH when the engine covers the phototransistor Q2.

  - R1 is set to give the desired acceleration rate as the train leaves the station.

• The 10K ohm potentiometer connected to C1 through a diode is used to set the maximum speed of the train. When the voltage across C1 reaches the voltage at the wiper of the potentiometer plus 0.7 volts it will stop charging and the train will not accelerate further.

• The throttle requires its own power source of 16 to 20 volts DC. The control circuit could also share this supply through a 12 volt regulator.

  The next schematic shows an abridged version of the Automatic Station Stop Circuit's throttle. This throttle "control section" might be used to control of a separate throttle through a SPDT switch.

  Exact wiring for this would depend on the throttle itself.

Abridged Throttle (control section)

  If you use any of these circuit ideas, ask your parts supplier for a copy of the manufacturers data sheets for any components that you have not used before. These sheets contain a wealth of data and circuit design information that no electronic or print article could approach and will save time and perhaps damage to the components themselves. These data sheets can often be found on the web site of the device manufacturers.

  Although the circuits are functional the pages are not meant to be full descriptions of each circuit but rather as guides for adapting them for use by others. If you have any questions or comments please send them to the email address on the Circuit Index page.