Chapter-3b Page 13
An LED Flasher
Many things flash around our roads and railroads. Turn indicators, warnings on utility vehicles, road works, ambulances, grade crossing advanced warning signs, airport beacons, tower warning lights and flashing signal speed indicators. This simple circuit, runs on 9 to 15 volts which is derived from the DCC track voltage. It can be put right where the light is needed. There is no control on the circuit, it will flash whenever the DCC voltage is present. The circuit is built around a type 555 timer [LM555, NE555 or similar] which is used in astable operation, ie. continuous. The capacitor and resistor, R3, determine the flash rate which can be varied by changing the component values. With the components shown it will flash at about a 2 second rate. A range of 1/4 second to 2 seconds is possible by changing the resistor to values as shown in the table. There can be one LED flashing on and off [with R1, L1] or with R2 and L2 added, the two LED's will flash alternately. The resistors R1 and R2 can be changed to alter the brilliance of the LED if needed.
This circuit works with colored or white LEDs. Amother option is to drive a string of LEDs in series using a lower resistance. For example 4 LEDs would need a 220R resistor at R1 and/or R2.
