DCC ImpulsesColumn - 5
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.
With that short introduction into theworldof optical detec-
tion, itwill beeasy tounderstandwhyDCCblockdetection is
anelegant solution. DCCblockdetection reportswhenever cur-
rent isbeing consumed inside the isolatedblock. That current
canbepoweringadecoder-equipped locomotive,whether it is
movingor not, or lighted cars (passenger or caboose), or cars
with resistorwheelsets. Formoredetails, seemyAugust 2013
column, referencedabove.
SoDCCblockdetection, coupledwith resistorwheelsets and
lighted cars,will veryaccurately tell you that theblock isoccu-
pieduntil the very last car exits theblock. There isonehitch.
Youneed tomake sure therearenoongoing current loadson
thedetectedbus, like: stationarydecoders, lit buildings, panel
displays, etc.
6: Drawing of a detected track blockwith signals outside
each end. The split in themiddle represents themissing
portionof a long block. If DCC detection is used, gapswill
be needed just inside the signals.
6
MRH-Apr2014
