The schematic (Fig 1) shows how the operation of a
stall motor can be further enhanced. IC-1 represents some kind of
rectifier that can be eliminated if the power source is DC. Only (1) IC-1
and C1 need to be used for the entire system. IC-2 along with
capacitors C2 and C3 can power clusters of up to eight controller
circuits. Using a voltage regulator is a bit of overkill as the circuit
will operate anywhere from 3 – 24 volts but it is cheap insurance to
make sure things don’t go wrong. The main requirements of the power
source is that the voltage can not drop below 3v during the AC ripple
of the power supply and remain above 8v long enough to drive the
The LM556 is
essentially a dual LM555 Timer but in this case it is wired as a latch
to boost the power output and to “remember” whether the “normal” or
“Reverse” button was pushed last.
(C4) sets the circuit to a known or default “normal” state when power
is first turned on. Note that I have several jumpers in series and
parallel so that signal lights can be inserted in various
configurations. Notice that the stall motor is essentially connected
directly to the output of this chip and that the polarity across it changes
with the state of the circuits.
interfaces to a computer and even then only to insure complete
electrical isolation and protection from any transient currents that
might be harmful. It can be completely eliminated from the circuit if
computer interface is not used. This chip contains four sets of
isolation circuits but only three of these circuits are actually used.
One is used to provide a signal to the computer which way a turnout is
currently thrown. Two more allow the computer to throw the turnout for
to route desired. Alternately, this device can also be used for
additional signaling. Turnouts can be controlled using switches or
buttons on a control panel, trackside switch stands that operate
electrical contacts under the table, or under computer control.
This system is
quite versatile. Multiple turnouts such as crossovers or double
crossovers can be connected together. A small “daughter” board
containing a number of diodes can also be inserted at the push-button
connections to control ladders in yards. Like all solid-state devices,
there is a small voltage drop across each diode that limits just how
far a ladder can be cascaded in this manner but I have found it
possible to cascade fifteen switches at a time with only an extra wire
or two. That should be enough for anyone.