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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 motors.
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.
The capacitor (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.
The LTV846 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.
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Building
a controller for stall motors is not a difficult project.
