Blinking tower light

Discussion in 'The Projects Forum' started by trackrat, Apr 22, 2009.

  1. trackrat

    Thread Starter New Member

    Apr 22, 2009
    I am building an N-Scale model railroad layout. I have a radio transmission tower on it and want to make the grain of wheat light on top blink. Not a simple "off-on" blink which I could easily do with my PLC, but a blink that gradually brightens and dims ove say a five or six second time period like they did in the old days. I was looking at RC time circuits, but cannot figure how to have a large resistance in series with the RC reistance and still get a filament to glow.


  2. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    Maybe something like this. But instead of the pot on pin 6, use two more LM324 amps and make a long period (6 second) triangle wave generator to drive pin6.

  3. KL7AJ

    AAC Fanatic!

    Nov 4, 2008


    Just an interesting point. Radio towers achieved the slow glow not by intent...but because the lamps had such huge thermal mass. Typically a top beacon lamp will have 2 X 600 watt bulbs up there. They are designed not to run efficiently, but to run a very long time, so they have very heavy filaments that run relatively cool :) Now, nearly all broadcast towers have gone to strobe lights...even during the night. You can tell they're strobed by shaking your head while looking at'll see a series of "trails". (YOu can also do a Bronx cheer and get the same results. Just do this alone. :) )

  4. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
    To answer your question, it will probably be best to drive the lamp through a transistor, and use an RC time constant on the base of the transistor to simulate the "cool down." For best realism, you might want to play around with the linearity....using a little bias adjustment. Brightness of a lamp is NOT directly proportional to voltage OR current, so you will have to fiddle with the time constant and "gamma" a bit.

  5. SgtWookie


    Jul 17, 2007
    Check out the "Fading Red Eyes" circuit about 1/2 way down this page:

    Yes, Bill Bowden used his circuit to drive LEDs, but there's no reason that you can't use higher-current transistors like 2N2222 or 2N2907's, and replace both the LEDs and the 100 Ohm resistors with your bulbs. However, your setup would probably last quite a bit longer if you used miniature LEDs for light.