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That should work, but with one issue I can see.  With the issues I've heard about with alignment of the Lionel Acela IR link, I wonder how reliable it would be on curves, etc?  Also, you need a bit more logic wrapped around them to switch the lights, right?  The good side is that there's no interference with other consists, that's one issue to contend with with RF links.

Right.  As I said, this is a germinating thought.

So I cobbled together a simple experiment as shown in above video.  On the left is an IR LED (transmitter) driven by a nominal 20 mA.  This would represent what is transmitted by the powered car when the tail-light is ON.  On the right is a widget that I built some time in the last century which I use to detect the presence of Infrared (IR) energy.  I've written about it in previous OGR threads.  Basically, when IR energy is present the red LED turns ON.  The red LED gets brighter with more IR energy.  It is powered by a 9V (DC) battery.  The idea is this is essentially what would be the repeater circuitry in the intermediate/intervening cars.  When IR energy is detected from the previous car, the 25-cent circuit would repeat the tail-light on/off state via an IR LED (instead of the red LED) on the other end of the car to the next car.  And so on.

The experiment was to place the receiver about my guess of the distance between two subway cars....then to rotate the receiver to simulate going around curves.

The video suggests we're in the ball park!  I believe you can reliably detect the IR transmission from an adjacent car even going around curves.

As mentioned earlier, this only makes sense if already opening up the intermediate cars to convert from power-hungry bulbs to LEDs.  It is a very simple and inexpensive circuit to detect IR energy with an IR detector at one end of the car...and then re-transmit the on/off status to an IR LED at the other end of the car; this daisy-chains the on/off status of the tail-light to the end-car.  No "software" or fancy digital circuitry is required!

Last edited by stan2004

Looks promising, Stan, what happens if the receiver is off the axis of the transmitting lens?  I'm wondering how wide the beam angle is coming from the transmitter.  Your demo kept it right in line with the transmitter and only changed it's angle, just curious how far off-axis it can be and still see the beam.

Agreed my experiment was simply to see if in the ballpark.  This was one of those "raise the flag and see who salutes."

The LED and detector each have angular-displacement specifications.  In the case of the LED this characterizes how the intensity changes as you go off center (rotated).  Likewise for the detector, this characterizes how the sensitivity changes as you go off center.  For example, from the datasheet of one particular 3mm IR LED, the intensity is 90% if 10-degrees off center, and 80% if 20-degrees off center.

angular displacement

If this hobby project was "engineered," one should do-the-math to show if enough IR energy makes it across the gap going around an O-31 curve (or whatever the worst case curve is needed).  Likewise, to your point, the TX and RX devices will be slightly off-axis...this could be horizontal and/or vertical mis-alignment. For the matter at hand, I suggest an off-axis error can be converted to an off-center error and the parametric datasheet graphs can be used.

anglular equivalence

This is offered in the spirit of a discussion forum.  Again, this method would require modifying each car in the consist.  Hence, I commented that this would probably only make sense if already planning to open up the middle cars to, say, convert from bulbs to LEDs for the interior lights.

But if there's any interest in this method, even if only for discussion purposes, we can press forward.

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Last edited by stan2004

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