The microcontroller takes care of all the de-bouncing and timing and switching functions which are usually handled by op amps and transistors. The resultant savings in parts allow the entire circuit to be constructed on a 1" X 3" circuit board
http://www3.sympatico.ca/kstapleton3/BD3A.HTM
There were several characteristics I desired in a block occupancy detector. They were low cost, isolated output, hysteresis, high sensitivity, and minimal voltage drop. Other desirable traits included simple power requirements, adjustable sensitivity, and some sort of built-in monitoring for testing.
http://www.geocities.com/ResearchTriangle/Thinktank/1096/detector.html
There are a few situations when an optical detector is better than a current detector. This detector uses the same PC board as the Rev H current detector, but with value changes and added jumpers. Sometimes a direct indication of train position is desired.
http://www.rr-cirkits.com/ir-detector.html
This page is about a block occupancy detector that uses optoisolators to electrically separate the track from the detector output. Three versions of the detector are shown: Basic, Time Delayed and Direction Indicating.
http://home.cogeco.ca/~rpaisley4/OptoBOD.html
This page shows a successful attempt to operate block occupancy detectors for DCC systems in a closely spaced group and with cabled wiring.
http://home.cogeco.ca/~rpaisley4/xDetGroup.html
This circuit senses the flow of current across the rails when a locomotive or resistance equipped wheel set is in the block. Whenever there is a large enough current flow the detector will produce an output indication. The circuit requires no adjustment and indicates the direction the train is traveling and can provide a steady state output for controlling block signals and interlocks.
http://home.cogeco.ca/~rpaisley4/BODGP.html
This page is about a block occupancy detector that uses optoisolators to electrically separate the track from the detector output. Three versions of the detector are shown: Basic, Time Delayed and Direction Indicating.
http://home.cogeco.ca/~rpaisley4/OptoBOD.html