Block Detection is there a better way? : LUSENET : Wiring for DCC : One Thread

I am new to DCC and have never tried block control. I am planning a new large (for me) layout 12 x 8 in HO. I have thought about block detection and was wondering why infrared emmiters and receivers could not be concealled in bushes or buildings etc. along the track to indicate block occupancy? I am not planning on using infrared walk around throttles. Thanks

-- Richard Gude (, September 18, 2000


There are two main types of infra-red sensors; the photo interrupter and photo reflector. Photo interrupters will work as you have suggested. You may need to skew the light path lengthwise down the track somewhat to avoid the on-off switching between cars as a train passes. You can even use reflecting objects like mirrors to make the effective path longer for better coverage. [Garage door and elevator door controls use this principal to sense objects in the doorway.] The reflector type sits below or alongside the track with the light beam shining out in space. When the train is present some of that light is reflected back into the sensor to detect occupancy. A time delay is used to avoid on-off switching between cars.

There are some problems to deal with. If you put many strong IR transmitters and sensitive recievers in the same room the light from one sensor will bounce off walls and ceilings to hit an unintended receiver, yielding poor results. Sunlight and even room lights can be strong enough to saturate the receiver, making it useless to detect the miniscule light output of the transmitter. Using IR filters help. The best systems modulate the IR transmitter and demodulate the recieved signal to separate out steady ambient light or that from another transmitter. [Commonly used for IR remote controls]

IRDOT sensors from SKD Electronics should work in the horizontal position as well as vertical. See

-- Don Vollrath (, September 19, 2000.

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