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I was just wondering if anyone knew how to make LEDs fade in and fade out as they flash.

I know Logic Rail has a flasher unit that makes LEDs fade in and fade out and my old NJ International flasher module in the following picture (no longer in production) makes LEDs fade as they flash
NJ International Flasher Unit.png

But I'm wondering if there's anything you can add to flasher units, like but not limited to the Circuitron FL-2 flasher unit, that can make LEDs fade in and fade out as they flash like incandescent lights do instead of just simply turning on and off. And I mean any flasher unit.

I also mentioned this in this thread about changing incandescent lights to LEDs

If only NJ International continued to make the pictured flasher, those were great for making lights, including LEDs, fade! By the way, the orange wires are what you connect to the power source (DC Power Pack used to power trains, or batteries, like a 9V battery or a 12V 8AA battery holder.) The blue wire is the Common and connects to the positive wire(s) and the green wires are what you connect to the lights or to the wires with resistors (negative wires.)

This isn't just for me, this is for anyone else who wants to know.


the circuit for fading is quite a bit different than for on/off operation .. it actualy feeds a gradually lower power, and / or longer interval to make it seem to fade
Which circuit would I have to use, and where would I get one? Unless Logic Rail is the only way to go.

I'll also ask Circuitron if they know a way to add a device to fade LEDs to their flasher units.


You might be able to use a capacitor / resistor circuit. What info do you have on your existing flasher unit and how many leds on each output? Also, what is the timing of the flashes on your flasher unit. Can't promise but I can have a play and see if it looks like being a possibility


Might take me a couple of weeks but happy to give it a go. The alternative could be replacing the flasher unit with a small Arduino board.. Shouldn't be too hard to devise something there using the analogue output pins.

John P

Active Member
From the videos,it seems that Logic Rail Technologies is doing it with a microprocessor, which I think is the right approach.

Edited to say I looked at their website, and found this:
"TrueLamp2" feature provides realistic fading in and out of lamps (common anode/positive LED or bulbs) while flashing. This feature is available beginning with version 3.0 of the board's main chip; contact us directly if you'd like to upgrade a previously purchased (prior to 2011) Grade Crossing Pro to this level.
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If you want to try something quick and simple, the diagram below will provide fading out of your LEDs in your crossing signals.

Sorry about the quick scrawl of a diagram. This assumes your flasher unit is configured for crossing signals with common anode LEDs
Resistors R1 & R2 are your LED current limiting resistors that you will need with or without the fade out circuit. Capacitors C1 & C2 are 16VW electrolytics, I found a value around 270uF to 470uF should give you suitable fade out delay. The diodes are generic 1N4001 rectifier diodes. All components should cost only a couple of dollars.

An alternative is to use a basic Arduino microcontroller and connect your crossing signals to the analog PWM outputs. You can then ramp the voltages up and down under software to achieve the fade you desire. Again, these boards are only a few dollars.

Hope this is of some help


Active Member
I've already coded and tested this idea (of a completely software driven method), on PIC, Arduino, and STM32 processors. Another thing you need to do, is condition the ramped LED output with gamma correction, because a mathematically linear ramp "bunches up" all the brightness at the top of the range. That produces a much less effective fade.

The details are too lengthy to go into detail here, but if anyone is actually trying it and needs help, PM me.

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