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Discussion Starter #1
Hi,

I'm doing this for the first time. I want a fully automated layout. I have JMRI and DCC++ working. Before I spend any more money, is occupancy detection (ie, current draw detection that will respond across the whole block) required? Or, if I was to use something else like IR sensors or RFID, can JMRI infer weather a block is occupied as trains pass into adjacent blocks?

Thanks!
 

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There are, as you have noted several types of track occupancy detection.

Perhaps one of the most popular are products of Azatrax.


Google "ho automated model train layout" and you'll see a number
of videos and texts on the subject.

Don
 

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You don't have to use current draw detection for a fully automated layout. That's what I chose to use for my layout, but many other people use IR detectors or magnetic switches. I'm not familiar with using RFID, but it should work too. There are advantages and disadvantages of each type of sensor. The most important is that whatever you choose, it needs to be reliable. You'll need at least one sensor for each block so that the software can track the train as it progresses from block to block around your layout. As mentioned, you should read everything you can about how to choose your blocks and where to put your sensors in your track plan. Its important that you have a sensor that is triggered at an appropriate distance from where you want a train to stop. The software uses the sensor as well as known speed of the train and time to compute an accurate stopping position. If you have specific questions, there should be several of us on this forum that can help.
 

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I want a fully automated layout. I have JMRI and DCC++ working. Before I spend any more money, is occupancy detection (ie, current draw detection that will respond across the whole block) required? Or, if I was to use something else like IR sensors or RFID, can JMRI infer weather a block is occupied as trains pass into adjacent blocks?
i believe three are 3 common options (see NMRA Block Detection)
  • IR detection
  • simple current detection w/o delay
  • current detection w/ delay
IR detection detects the presence of a car at a specific location. It could be located at one end of a block to detect that a train has entered a block, but it's not obvious how to "infer" that a train has left the block and more of an issue with traffic in both directions. IR detection can be baffled by room lighting. Azatrax switches the emitters to recognize background levels to improve reliability but i've read that modelers add heat shrink tubing to limit the aperture of the detector.

"simple" current detection using just a diode bridge, AC opto coupler and current limiting resistor and LED and current limiting resistor w/o any delay mechanism is fine to indicate that a block is occupied on a panel but may not be reliable enough for an automated system unless that softare implements a delay. A delay is necessary to prevent taking action when a block is no longer occupied such as "fleeting". Intermittent clears can result from intermittent contact when there are just a few cars in a block.

detection with delay, in addition to the components of a "simple" detector often include a larger capacitor and level detection logic with hysterisis (e.g. 555, 7414 Schmitt trigger)
 

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Discussion Starter #5
Thanks for the replies, lots to think about. I think I'm going to start with current draw detection on a small test layout and go from there.
 

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Thanks for the replies, lots to think about. I think I'm going to start with current draw detection on a small test layout and go from there.
The problem with current draw detection is that all of your car trucks must
conductive. There is a fluid you paint on the axles that 'shorts' the between the wheels
with a resistance.

Don
 

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The problem with current draw detection is that all of your car trucks must conductive.
I don’t think this is true. If you don’t have all the cars being conductive, the software will just have to compute when it thinks a block becomes free rather than knowing definitely when its free. This is really no problem. It’s true you get benefits by having all the cars be conductive, but it’s not required.
 

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or at least the last car with conductive wheels (e.g. caboose)
This would work as long as your train is always shorter than your blocks. You wouldn’t want your engine to pass out of the block before the end of the train enters it. That would really confuse your software because the block would appear occupied as expected, then unoccupied, then unexpectedly occupied again. You could solve this by placing some other cars with conductive wheels periodically within your long train.

I‘m not familiar with JMRI, but I’m currently using TrainController. It has multiple options for occupancy detection that allow for computing train lengths and sensor delay timers that can be used to accommodate most any detector type and train configuration. I would expect JMRI to be similar.

At this point in the build process, get your block locations identified first and worry about wheel conductivity later.
 

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That would really confuse your software because the block would appear occupied as expected, then unoccupied, then unexpectedly occupied again.
would it?

there would be a Stop signal in the block following the caboose and an Approach signal in the block after that. Does it really matter that the block with the caboose is reporting Approach
 

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Certainly not every car, but 10% may just give you enough coverage. A crossing gate/signal may take a combination of current sensing long block with the gates in the middle and optical sensors on either side of the gate to detect the end of train, sort of like in real life!
 

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would it?

there would be a Stop signal in the block following the caboose and an Approach signal in the block after that. Does it really matter that the block with the caboose is reporting Approach
You may be right. I haven't actually tried it and I can't give it a try since all my cars have conductive wheel sets. I'm guilty of making some assumptions here.

My best advice to someone new to automation is to learn from what others have done. Hardware and software developers have certainly made the common scenarios work, so you should be safe if you follow common practices. Going outside of common practices means you have less people that can help if you run into problems.
 

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Discussion Starter #13
Thanks again for all the replies. My layout is going to be a cityscape with short passenger trains, so I'm not too worried about trains being too long for the blocks. At least not yet... Would be nice to have cargo roll through once in a while.
 
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