Electronic hobbyists canfind schematics and kits tobuild
their own.
Detecting theentireblockbecomes an issuewithoptical sen-
sors. They caneasily tell that there is a trainabove them, but
not elsewhere in theblock. To report anentireblockoccupied
requires some foolingaround.
Onemethod istime.Once the trainuncovers theoptical sensor,
atimer startsand some seconds later, theblock isdeemedclear
and the signal logicproceedsnormally. If the train stops just
after ituncovers thedetector, the situationpictured infigure2
canoccur: agreen (or yellow) signalwitha train justpast it.
Increasedaccuracy requires increased complexity. Two (or
more) sensors alongwith sophisticatedelectronicswillmore
accurately report theblockoccupied. TheAzatraxMRD2 (7,
next page) is anexampleof this typeof board.
MRH-Apr2014
