Thursday, January 4, 2018

Experimenting with Infrared detection circuits

Looking at some different options to trigger the grade crossing signals that I am planning for the Battle Mountain section and thought I would try an off the shelf product that uses pulsed Infrared or IR light.  IR light would have an advantage over normal photocells because it is less likely to be effected by room lighting and would work even in the dark.  I still have my "test layout" with Kato Unitrack which will be used to check things out before actually installing anything on the main layout.

For my experimenting I am using the Azatrax MR8D board.  Power for it can be from 8 to 16 volts AC or DC.  It can support up to 8 transmitter / receiver pairs and provide a solid state contact closure output for each of the 8 channels.  Each channel has an LED indicator which lights when something breaks the invisible IR beam between transmitter and receiver.
The set came with pairs of transmitters and receivers with leads attached and styrene tube protecting the connection.  The devices themselves look like 3mm LED's.

The Azatrax instructions recommended setting the devices at an angle across the track so the beam would not pass through the space between cars.  I used flat head screws and cut the styrene tubes into short lengths to hold the devices.  A 1/8 inch brass rod through both tubes holds the alignment until the adhesive sets.
I installed one set at a 3/4 inch height and another set at 1/2 inch height.  I then made up a test train with one each of several types of freight cars.

The 3/4 inch height worked OK except for empty flat or well cars.  As the instructions had suggested, there was no problem at all with the spaces between cars using the angled arrangement.
The pair set at a 1/2 inch height worked well for the 50 ft flat car that failed on the 3/4 inch height but was too low for the tank car.

Thinking about how the lateral angle was used to prevent the signal from passing between the cars, I thought that using vertical angle as well could help

So I lowered the transmitter screw on the pair that I had set at 3/4 inch to 1/4 inch.

This worked the best with very few instances of the signal getting around or through any of the cars in the test train.
Where my grade crossing is the track has low hills on one side with some exposed rock.  My plan is to embed the transmitter in the foreground scenery at ground level and the receiver in the hillside scenery at a higher level.

This photo with the IR beam path drawn in shows how the sensors could be installed on the  approaches to the grade crossing.

The Azatrax IR detection circuit seems to work very well and come in several configurations.  To learn about what is available check their website.

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