5
GB
A feedback decoder must be provided with infor-
mation at its inputs. This can performed with po-
tential-free, train-activated switch contacts such as
switching tracks and reed contacts. Such “moment”
switch contacts have the property that they only
provide a pulse of current for the short moment in
which the train (or even a particular car of the train)
moves over the contact. This is not always sensi-
ble. For a PC control system, for example, it is de-
sirable to be able to directly recognize the occupied
sections of the route after the system is switched
on. Coaches or wagons that are left standing
should also be recognized. This requires constant
contacts that provide a signal for as long as the
monitored route section is occupied by a vehicle.
For certain third-rail track types (Märklin C and K
track), this can be achieved using grounding rail
sections insulated on one side (“contact track sec-
tions”). A vehicle located on it bridges the left and
right grounding rails, thereby triggering a signal.
However, this quite simple procedure to detect
occupied track sections does not work in turnout
areas, because the left and right grounding rail
sections there can only be electrically separated
from each other with a lot of handwork. This type
of occupied detecting is also not possible for tracks
without a third rail. For this track type, both rail
profiles have a different polarity, and bridging with
an uninsulated set of wheels would lead to a short
circuit.
Our feedback decoder with track occupancy de-
tector 5233 was developed to solve this problem.
It consists of a “half” feedback decoder 5217 on
whose 8 inputs sensitive electronic current sen-
sors are connected (via “optocouplers”). On these
current sensors, you can then connect either the
turnouts areas of third rail tracks (i.e. their insulat-
ed third rail) or the sections of tracks insulated at
one side without third rail (two-rail / two conductor
system).
The current sensors recognize every power-con-
suming vehicle on the monitored section of track.
These can be locomotives or illuminated cars with
their own power pickups (center slider, wheel con-
tact).
For two-rail systems, it is also possible to bridge the
axle insulation of the wheel sets of unlighted cars
with high resistance using resistor paint (do not con-
fuse with silver conductor paint!). This makes the
cars (slight) power consumers so that they are rec-
ognized by the power sensors of the 5233. Resistor
paint (Uhlenbrock item no. 40410, 10 ml) is avail-
able at specialty stores for model railroad material.
As an alternative for H0, the resistor wheel sets
(40186 and 40187) from Roco can also be used.
For the track occupancy detector in the 5233 to
work, it is necessary for there to be a digital volt-
age on the track. The internal voltage monitoring
system of the 5233 makes sure, that in case of an
interruption of the digital voltage in the monitored
sections the last occupancy reporting status is “fro-
zen” and saved. If the digital voltage is switched
on again, the data of the last occupancy reporting
status can be used.
3. Connecting the Decoder to
the Digital System
The decoder is connected directly to the 6-pin s88
socket at the rear of the Memory or the Interface
(Märklin or Arnold), of the Intellibox (Uhlenbrock),
or the Twin-Center (Fleischmann) via the included
special cable, with the power of the digital system
switched off. Be absolutely sure the special plug is
positioned correctly (see the picture at page 1). It
must be inserted in all devices so that the ribbon
cable runs downward.
The use of a long chain with many long s88 bus
cables is susceptible against distortions, caused
by driving locomotives or switching magnetic de-
vices for example. So we recommend to place all
feedback decoders at a common area of the lay-
out, preferably next to the central unit. From this
point the single wires go to the track contacts and/
or track sections. However, if you should need a
longer bus cable in an individual case, you can ex-
tend the enclosed short cable with the s88-exten-
sion cable
Viessmann
art.no. 5230 to 1.65 m.
Up to 31 feedback decoders 5217 or 62 feedback
decoders with track occupancy detectors 5233 can
be connected to the Märklin Interface, the Fleis-
chmann Twin-Center, or the Uhlenbrock Intellibox.
This means that one feedback decoder 5217 (16
inputs) is replaced by two 5233s with 8 inputs
each. The total number of decoder inputs can be
up to 496.
The feedback decoder with track occupancy de-
tector 5233 and the feedback decoder 5217 (or
s88) can be combined with each other in any se-
quence.
The decoders are automatically numbered in se-
quence from 1 to 31 by the central control unit or
the interface. Every two consecutive 5233 decoders
get the same address (see Figure 1).
Therefore always place 2 decoders 5233 directly
behind each other in the chain. Otherwise offsets
in the automatic address assignment occur. A 5217
or s88 would then belong half to one and half to the
next address. This is allowed in principle, but leads
to confusion.
