DBD2 - DCC Block
Detector
Discontinued
The DBD2 is a dual block
occupancy detector. It provides complete isolation from
the track by using small transformer type sensors. This
also means there is no drop in track voltage as there is
with sensing diodes. The DBD2 is designed to work well
with the SIC24 signal and indicator
controller. In applications where relays are required
it has enough output current capability to drive them
directly.
MSRP - 19.95 USD
Manual in PDF format - 40K
Color
Picture
Board size: 1.5" X 1.8"
Operation:
The DBD2 is capable of sensing current in two isolated
sections of track called blocks. This provides for
detecting the presence of locomotives or other rolling
stock that draw current from the track.
The track feeder wire for one rail of the block is passed
through the hole in the sensor (see diagram below) before
connecting the feeder to the track. When the current in
the feeder going though the sensor reaches the trigger
level, the output is turned on and the LED lights showing
the block is occupied. Passing the feeder though the
sensor more than one time will increased the sensitivity.
However, this is NOT recommended because the maximum
sensor current specification will be greatly reduced.
Locomotives and lighted cars draw enough current to
trigger the DBD2. In order for other rolling stock to
draw current, resistive wheel sets will have to be added.
For HO scale, one 4.7K ohm resistive wheel set will work
per car. If you want to use 10K resistive wheel
sets you will need two wheel sets per car.
Duty track can cause intermittent current flow. A built
in filter keeps the DBD2 from rapidly turning off
and on if the current flow is interrupted. Additional,
there is a small amount of hystersis so that small
changes in track current near the trigger point do not
cause the DBD2 to turn off and on. The filter keeps the
output on after a train leaves the block for a short
period of time. This time is typically about 1 to 2
seconds. The amount of track current has an effect on
this time.
Since the DBD2 does not use diodes to sense track current
there is no drop in track voltage. This allows you to
“double sense” a block. For example, suppose
you want to add a grade crossing with gates and flashers
to a section of track that already has a diode sensing
block detector. The block could be cut into three smaller
blocks to detect traffic on each approach and island
blocks. DBD2s can be used for the three new blocks with
out interfering with the operation of the original
detector or causing an additional track voltage drop. See
the SIC24 signal and indicator controller for information
on implementing a grade crossing.
Detector Output:
The DBD2 output configuration is a push-pull and can sink
and source current. The output is typically connected to
a signal system input. However, the DBD2 has enough
current capability to drive a relay. There is clamping
diode build in so no external diode in required when
driving a relay.
Specifications:
Operating voltage: 5 to 15 volts DC
Operating current: 6 ma @ 5 volts, 10 ma @ 12 volts
Maximum output load: 400 ma
Typical trigger current: 3 ma @ 5 volts, 6 ma @ 12
volts
Maximum sensor current: 5 amps w/one pass of feeder wire
