I’ve come back to this project as the opportunity to do lighted markers has finally become a possibility for me. For reference, here is a pic of the prototype:
And my model:
The lights I’m modelling are those construction barrier lights hanging on the end. Until recently I had no idea how I would ever model them, but I’ve always wanted to. One because they are so small, and two because they would be flashing and who doesn’t love flashing lights, right?!!!
I started casting LEDs into ditch lights and such way back when Intermountain released their SD40-2W. I got a CN model and cast porch mounted ditch lights.
Sorry for terrible shot. It’s the only pic I have.
Later I did a more complicated install with pairs of LEDs cast into stands on both ends of this BC Rail CRS20:
All of those LEDs were 0402 which are really small, but would be way over sized for this install. The light I’m modelling is only about 6” across.
Two things happened that brought this project back to the forefront. First I found 0201 LEDs which are TINY! I successfully soldered them for the first time here:
https://www.therailwire.net/forum/index.php?topic=48102.0The second was when
@CNR5529 produced THESE for me on his Photon!:
Yes, those are scale sized construction barrier lights.
I created a mold for the master:
And cast an LED into it:
When finished it looked like this, sorry about my giant gross fingers:
The next step was to work on some circuitry. The first piece is the constant lighting circuit that
@peteski designed for me a few years ago here:
https://www.therailwire.net/forum/index.php?topic=29654.15With constant lighting done, I needed a way to flash the LEDs. Construction barrier lights never flash at the exact same frequency. They always seem to be just a little out of phase and this was a feature that I wanted to have. I searched for led flasher circuits and finally stumbled on a CRAZY simple circuit on YouTube:
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The Coles Notes version of it is that you use an NPN transistor and feed positive voltage into the emitter side. As the capacitor charges it eventually reaches the break down voltage and allows the transistor to conduct, lighting the LED until the charge in the capacitor drops below the break down voltage, and the cycle is repeated repeated. Aside from the LED it has three components... doesn’t get any simpler than that! Small is good as I have to jam two of these circuits and the keep alive inside this little caboose.
I experimented with cap and resistor values and eventually settled on a 470uF cap with a 2.7k resistor. I used this combo as it created the strobe effect/frequency I wanted and I have some 470uF tantalum caps that are tiny. At first I was using different values of resistors for each circuit but I found that they had an effect on each other which would cause anomalies like different decay rates, perfectly timed alternate flashing, one LED being lit solid etc. The reasons for this are beyond me so I just kept plugging in values until I found something that worked. Eventually I ended up with a 2.7k resistor on one circuit, and a 3 LED series combo that created the perfect effect where the LEDs go in and out of phase about every 30 seconds. Turns out, that three led combo was 2.7k! So I used two 2.7k resistors. The reason for the different frequencies of flashing must be due to the variance in tolerances.
Here it is on a bread board:
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And connected to my cast lights:
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Here is the final design I settled on, with values:
Next I had to package it. I didn’t want to make a board. I wanted to make it even more compact so I did something similar to the keep alive circuit, and built it around the cap:
Next I wired the three circuits together into one complete bundle:
The bottom side shows the four connections for the LEDs
And the top view shows the keep alive circuit piggy backed on top:
I covered the whole thing in silicon to insulate it.
That’s where I am so far. The next step is to model the mounts, paint/install the LEDs on the caboose, and install power pick up in the trucks.
Craig
