Chapter 5c-1 Page 31
Flashing Signal Aspects Some signal light aspects are steady and some are flashing. Why?
Well, by making one of the lights flash it is effectively adding a 4th aspect to a three lamp head. The most common is an advance approach light (Yellow flashing) and this informs the engineer that the second signal ahead is at Red and speed must be reduced to enable a complete stop. Necessary in these days of long heavy trains. While a flashing divergent advance approach would indicate a turnout ahead and to be prepared to stop at the second signal. In some systems it can indicate that the train is approaching an area (junction/loop etc.) where the approach normal speed is changed to an approach limited (higher) speed. I would expect there to be a set of high speed turnouts ahead. A Red flashing or Marker board flashing allows a proceed at reduced speed which over-rides the stop and stay condition of a normal Red aspect. I can find no real information on dwarf signals flashing but as they are usually only 2 aspect it perhaps doesn't apply although I believe SP flashed Green under some conditions. Interestingly in the United Kingdom a flashing yellow would indicate that a train is to take a diverging route ahead with a lower line speed than the main route, indicating to the driver to slow the train down in time for the speed limit of the diverging route as opposed to slowing even more in preparation for a stop signal. The micro switch shown in the schematics would typically be connected to a turnout throw bar or possibly be a block detector relay.
Reference these web sites for more signaling information :http://www.railroadsignals.us/ - for a reference to Color Position Lights. http://www.davros.org/rail/signalling/articles/junctions.html - U.K. systems http://www.railroadsignals.us/rulebooks/rulebooks.htm from a selection of railroads
What circuit do I use ? If your signals have a common wire that is positive - use PNP If the common wire is negative or ground - use NPN But not on signals with a common dropping resistor in the signal. The Green Flashing LED This 5mm diameter device contains an IC oscillator circuit in series with an LED. This allows it to be driven from a very wide voltage range from 3 to 15VDC without any external components required. The LED itself produces a bright output of 500mcd (typical) making it suitable as a very notice ďž able warning lamp in alarm panels, car and boat dash boards, etc even in daylight The series 6K8 ohm resistor reduces the brightness as it is not being used as an indicator in this circuit.
