NCE provides the BD20a current sensing based block occupancy detector. Therefore NCE BOD20a shares to NCE BOD Version 6. The NCE BOD V6 series of occupancy detectors are current based detectors. The sense the difference between a open circuit on the track (nothing conducting current) and closed circuit on the track (Something conducting current). The advantage of current sensing detector is that the entire block of track is monitor form end to end. It does not matter where the car or engines is on the track. Track power consist of two wires, one for each rail. The circuit requires one to install the detector in series with one of the rail track feeds. We call this rail the detected rail.

The track feed must be the main wire that all the track feeds are tied into. Stated another way, all the track feeder wires for the rail must be reduced down to a signal wire before it passes through the BD20a or BOD V6. It connect to NCE motherboard. I inspired by NCE. After that I will change the update in the further. There will get better soon.