I have long wanted to have operating signals on my model railroad. These are the signals that flash to tell motorists of an approaching train. These are commercially available but I enjoy the problem-solving challenge of scratch building something myself so I thought I would take this on as a new project. This is the first of four blog entries on this topic which will include:
Part 1 of 4 - Building the Crossing Lights
Part 2 of 4 - The Methodology for Train Detection
Part 3 of 4 - Designing the Circuit
Part 4 of 4 - The Code
I first needed to determine the dimensions of crossing signals. A quick online search of "Canadian Grade Crossing Standards" located the following Transport Canada site which contains graphical images and dimensions along with far more information than I will ever need: Transport Canada Grade Crossing Standards. At the bottom of the page is a link to a 60-page PDF file that also contains all the information.
For those readers familiar with the US-style sign which has the words "Railroad" and "Crossing" on the crossbucks, this style has not been in use in Canada for decades. Being an officially english/french bilingual country, Canada removed all words from its crossing lights. This is a graphic taken from the above-mentioned guide:
While the above guide was helpful I wanted to see some real-world pictures of some signs because, depending on when the sign was constructed, the physical appearance of the sign components vary. Using Google Maps to look up crossings within a few kilometres of where I live I quickly was able to take screen shots of a few samples. Here is one:
Using a punch I cut sixteen 7.4 mm disks out of 0.01" thick styrene and in the centre of eight of these I cut a 3 mm hole. The other eight were cut to remove about 1/3 of the area. The following picture shows the first cut on the left. One of these is then turned into the piece in the centre (which houses the light) and the other is turned into the piece on the right (which shades the light).
I wrapped the shade piece on the right around a steel rod that was approximately 4 mm in diameter and held it place for a couple of hours with a clamp to create a slight bend. I then placed it on the light housing, applied a small amount of liquid styrene cement and coaxed the shade into position, holding it a few seconds as the cement dried.
Next, I built the lights that slide into the above housing. The following shows two red 3 mm LEDs. When working with LEDs it is extremely important to keep in mind that, unlike incandescent light bulbs, LEDs are polarity dependent. They will only work if the anode (the longer leg) is powered from the positive side of a power supply and the cathode (the shorter leg) is connected to the ground or the negative wide of the same power supply.
I decided I would use a 3/32" outside diameter hollow brass rod for the pole. In this way the pole itself can be used as a conductor of electricity. Each leg of the two LEDs will be soldered together and, in turn, ONE of them soldered to the outside of the hollow brass rod. In this way the brass rod acts as a conductor and only two thin wires need to be passed up through the hollow brass rod and connected to the other joined legs. I decided that I would wire my LEDs with common anodes (the long, positive legs of the LEDs). However, as I needed to cut both legs of each LED to be much shorter I put a small black dot on the side of the anode (positive) side of the LED at this stage so I didn't get confused over which was which when the legs are shortened.
I pressed one of the cutoff LEDs onto a wooden toothpick, as shown (note the black mark denoting anode):
I then added a second LED from the other side and soldered both legs together.
Using one of the legs that I had earlier cut off I soldered the common anodes together, as follows:
I then repeated the process to create the lights for the other crossing light:
Using a small file I cut a small opening in the wall of the hollow brass rod which is where one thin wire will pass through to the cathode (negative leg) of one of the pairs of LEDs and another thin wire will pass through and be soldered to the cathode of the other pair of LEDs. I then soldered the wire connecting the common anodes to the outside of the hollow brass rod, on the side OPPOSITE the location of the hole, as follows:
This photo shows the wires soldered in place. The red wire is soldered to the bottom of the brass rod. The blue and black wires are both fed through the tube and out of the hole. The blue wire is soldered to the cathodes of one pair of LEDs and the black wire to the cathodes of the other pair of LEDs.
Using the techniques described in my blog post of April 21, 2021 I created the crossbucks and "2 tracks" signs. I then glued the styrene light units onto each LED after painting them black and the signs to the post. I fashioned an electronic bell out of hollow styrene rod and glued it to the top of the pole. Finally, I painted the pole metallic silver.
This is a picture of the finished crossing lights:
