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Tuesday, January 2, 2007

Lessons Learned - Block Detection Approaches

As I have been studying the pieces and parts of computer control for model railroading, one of the more complex issues is how exactly should I do the block detection. I am talking about the physical layer, the hardware to be installed on the layout. Here is my analysis of the four commonly accepted approach methods for doing block detection.

While I have determined current flow detection approach is best for my uses your situation may be very different. Certainly some situations on my layout will not be current detection, but my intent is to use that approach as much as possible. Good luck with your railroad automation!

Detection Approach Rankings

Current flow detector 2.67

Totally invisible, works without light, highly reliable, variable block size benefits offset high cost and difficulty of install. Locomotive and all lighted cars or cars with resistive wheel sets are detected. Detection can be along a very large section of track. If installed at layout construction, minimum impact. Does require gaps in the track which can be cut with a Dremel after installation.

Photocell (CDS) 2.33

Easiest implementation, lowest cost, but does not work in the dark. Spot detection only.

IR Photocell 1.89

Very visible, difficult to conceal, susceptible to ambient light, requires alignment and is likely the most difficult installation. Spot detection only.

Magnetic reed switch 1.89

In some cases the locomotive installation can be fragile and difficult; keeping sensor and switch magnets in alignment result in maintenance issues. Only the cars with magnets are detected. Spot detection only.



Criteria explained

Works in dark - Is not dependent upon room lighting

Installation - Easy to install, requires minimum number of wires and no external power requirements

Durability - Not easily disturbed, does not require alignment

Reliability - Not easily triggered falsely, and room lighting does not affect

Block Size - The entire length of the block is monitored with a single sensor vs. spot detection

Cost - Minimum cost is $2.00 max is $10.00 per block plus wire and labor.

Loco mod required - No modification to a locomotive is required for operation

Conceal ability - Detector is totally invisible, no components can be seen on the layout


1 - Lowest score, minimum, below expectation, missing.

2 - Average, acceptable, meets expectation

3 - Highest rating possible, excellent, exceeds expectations!


Copyright 2007


Mike Tennant, on Trains Forum made me aware of the Sensa-Track IR detection system.

So I did some reading on the Sensa-trak device as their website. Interestingly the product is almost as expensive as block detection 8 vs 10 bucks, relies upon ambient light, which means it will not work in the dark and of course it is a spot sensor. While I think they overcome the issues with installation, they loose much of value of the infrared capability by using ambient light. My 2 cents worth of observation.

DIY IR Block detection

Here is a site with a DIY, do-it-yourself IR block detections system the author claims can be built for about 7 bucks worth of components, if you have the patience and considerable skills to master. However, it is still IR and carries with it the inherent issues associated. Still it is interesting to see the creativity and engineering.

Block Detection Strategy
How are you implementing block detection?
My layout is mostly under block detection
I am doing limited block detection
I am planning block detection this year
I have no plans to do Block detection
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