Circuits Basic flasher - Utility circuit, DCC powered

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.

Components:

LM555 timer I.C. (MC4555 and many other variations - but don’t use ICM555’s) W04, 1.5amp bridge rectifier - Round form

Capacitor 1.0 ufd tantalum capacitor - timing capacitor 10 ufd 25volt axial electrolytic capacitor

Resistors 2,200 Ohms - [2k2] 1 meg Ohms - [1M0] or as required - see table 1k0 to 1k8 dropper resistor (R1 and R2) P C Strip Board (Vero board type) 15 x 7 rows. Another view of the components layout

Optional timing resistors for R3

ON/OFF Time 1m0 - 2 seconds 560K - 1.5 seconds 220K - 0.6 seconds 100K - 0.25 seconds

390R 1K2 33K 47K 1M0 390 Ohms 1,200 Ohms 33,000 Ohms 47,000 Ohms 1,000,000 Ohms 2 1 1 3 2 orange-white-brown brown-red-red three orange bands yellow-violet-orange brown-black-green

| orange-white-black-black | brown-red-black-brown | orange-orange-black-red | yellow-violet-black-red | brown-black-black-yellow