DBD2 - DCC Block
Detector Application Information
Detector for
SIC24:
The DBD2 can be used as a block occupancy detector for
the SIC24. The DBD2 can operate from 5 volts which the
SIC24 provides on it's input connectors. The DBD2 output
voltage levels are then compatible with the SIC24 inputs.
See SIC24 application information for a diagram of two
DBD2s connected to a SIC24.
Sensitivity Issues:
There are several reasons why the DBD2 may indicate a
block is occupied when in fact there is no engine or
rolling stock in the block. If there is a LED or some
kind of indicator that is powered from the track, this
could cause the DBD2 to show occupied. High humidity
conditions can cause a problem. Perhaps the ballast
is damp for some reason. Water can act like a resistor
between the rails. There can be enough distributed
capacitance in the DCC wires to cause a small amount of
current to flow and thus causing a false indication. To
keep the capacitance to a minimum, place the DBD2 close
to the block it is detecting. Keep the the block feed
wire or any of the block track feeder wires from running
right next to other wires for long distances. Do not
twist the block feed wire with another wire.
In some cases it may be desirable to decrease the
sensitivity of the DBD2. This picture
shows where to solder resistors to decrease the
sensitivity. A 2.2K resistor will give about a 20 ma
trigger current. A 1K resistor will give about a 75 ma
trigger current. If possible use a 1/4 watt resistor.
Also, keep the resistor leads short.
You can use the DBD2 for over current warning by
connecting a buzzer to one of its outputs. Using a
resistor in the 22 to 27 ohm range will cause the DBD2 to
trigger in the 2 to 3 amp area. Experimentation will give
you the exact trigger point desired.
Remote LED Indication:
The DBD2 can be used to drive a remote LED to show block
occupancy status. The first diagram shows the DBD2
driving a remote LED. When the block becomes occupied the
DBD2 turns on the LED.
The next diagram shows the DBD2 controlling a two
lead bi-color LED. When the block is unoccupied the LED
is green. When the block is occupied the LED is red.
In each diagram only output 1 of the DBD2 is shown
connected. Output 2 could be connected in any of the ways
as output 1.
When driving a LED a resistor is required to limit the
current in the LED.
Detector Label:
Gerry Albers provided identifier template labels for the
DBD2. They have a place to label the output and power
connector terminals. Version 2 has a box to write the
Power District identifier and the rail (Rail A or Rail B)
being detected. These templates are set up to print on
business card stock, Avery #8376. Only the bottom needs
to be trimmed after printing. They are intended to be
placed under the DBD2 where it is mounted.
Label
Label2