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A WIRELESS THROTTLE
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A local
switcher starts the day at Bobston
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An engineer picks up a throttle and begins his
run. He can select an origin, then
select a turntable stall and bring his engine out of the roundhouse. His train passes a signal and it turns
from green to red. He stops at a
major turnout and can throw it for the main or diverging route. At the end of his run, he releases his
train to the yard crew to take over.
The throttle described here contains all of the
above functionality from well over 300 feet. Yes, a computer and train detection units
are involved, but the wireless throttle controls all.
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The wireless throttle on the North River Railway
is a rather unique blending of the old-time transistor throttles of the
fifties combined with modern integrated circuit technology then merged with
a computerized block control system.
The main function of the throttle is to control the speed and
direction of a train however; it also sends signals to a computer interface
to operate auxiliary devices including turntables, switch machines, and
signals.
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I do not pretend this throttle to be the next
generation of control after and/or instead of DCC. It is simply a product of tinkering over
many years as an approach to watching the train, not the control panel.
Block systems require the engineer’s constant attention as the train
travels along and can become quite complex on large railroads. DCC systems may work extremely well to
prevent this but also have certain limitations.
Locomotive space for receivers often means a
slight reduction of weight for pulling power, the programming for the
acceleration curve is complex, and getting started with DCC can be
expensive. The main problems are
that things do go wrong, standards are poor, and devices burn out much the
way they did back in the fifties. It
is also very harsh on motors.
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Computer
for controlled block system
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This Throttle, when combined with a computer control, provides a
rock-solid wireless control of trains with many features not available on a
typical DCC system including:
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Range of 300’
indoors using internal antennas - 1000’ with external.
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Over 750
control channels possible
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Personality
modules to customize characteristics for engineers or types of engine(s) with simple plug-in
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No decoders
or other modifications required to engines.
Will run both unmodified and DCC/DC modified engines
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Will not
harm brushless or permanent magnet DC motors
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Simplified computer
compatible interface for Accessory control
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Anti-reverse
lockout protection at running speeds to prevent jamming of gears.
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Other
features too numerous to enumerate here.
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Building this throttle (if you have already cheated and looked at
the schematics below) may seem like a daunting task. Let me assure you there is nothing
critical in its construction and most of the features have appeared in
other articles. Just in case though, please SEND
AN EMAIL to let me know if you find any errors.
Throttles have about the same general configuration as shown in the
diagram below. You will find each of
these elements in many designs so a good understanding of each element is a
good place to begin
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The power supply converts dangerous house current
to a safe level to work with. It also converts alternating current to
direct current and should have a fuse to protect equipment from severe
overheating due to derailments and shorts.
The output of the power supply made available to each element of the
throttle circuits.
The controls found on a regular power pack
usually consist of a simple rheostat and a reversing switch. The control and distribution elements
separate these in a transistor throttle.
A rheostat is essentially acts as current limiting device by varying
a resistance from 0 to about 50 ohms.
The potentiometer is a voltage divider. Its resistance in the circuit is constant
but its output voltage varies from 0 to some amount, often in the magnitude
of just five volts. Push buttons and
resistors may replace potentiometer in circuits containing a momentum
capacitor, especially where a transmitter/receiver interface is involved.
The interface of an old time power packs is
simply part of its internal wiring.
For an early transistor throttle, a long tethered cable allowed the
operator a certain degree of freedom to walk with the train. Modern throttles seem to have some type
of transmitter/receiver arrangement of some type, infrared and radio
frequencies being the most common.
No matter what type of interface is used, it is simply a way to
deliver a signal to the momentum section that is in proportion to the
setting of the controls to the momentum section.
The momentum section is essentially a capacitor
where the charge on the capacitor controls the speed of a train. There are many ways to change this
charge, all of which involve resisters and diodes.
We now come to the conditioning section. This is the black box where a throttle
works its magic and blends the pure DC from the momentum section with any
of a number of waveforms. Sign,
triangle and square waves (as either AM or FM waveforms) can also be added
to improve the performance of an engine.
The amplifier uses this modified waveform to power the train. A
DCC system decoder performs all these functions using mostly programming
instructions instead of hard wiring to manage its internal circuitry.
The Amplifier is essentially one or more power
transistor that amplifies the low-power waveform from the conditioning
circuits to enough power to drive a train.
Protection circuits guard against shorts, the high voltage spikes
generated by the locomotive’s electric motor, and whatever other hazards
that may exist.
The distribution element is usually straightforward. A reversing switch or relay changes the
direction of an engine and block switches allow for multiple train
operation. This throttle is a bit
unusual in two ways. First, two
relays are used to change the direction of an engine such that it runs at
equal speed in either direction.
There is also a circuit to prevent the jamming of a forward running
engine into reverse while running above a preset speed.
Look for these elements in the detailed
description that follows
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TRANSMITTER / CONTROL
The hand-held throttle or more properly the throttle control uses
five push buttons for the control of a train. The Black buttons control the forward and
reverse, The blue button I for acceleration, the yellow is the service
break, and the red button is for emergencies. The red button also signals the computer
that a cab is in use.
The three grey buttons are used for auxiliary functions
The slide switch on the end is the on/off power switch and the three
pins barely visible on the side if for charging the battery without having
to open the box
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This view inside the box shows the battery located to the
right. This gives the box a nice
balance when held by this end.
The PC board on the left contains the Transmitter module and antenna. Note that the antenna is as far from the
user as possible.
The center board contains most of the circuitry required to send a
signal at every key press.
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This close-up shows the groves cut to separate
the pads required for the transmitter module. Groves are cut first with a knife then
widened with a triangular file. The
orange area on the bottom of this view is the copper cladding laminated to
the backside of the circuit board that acts as a ground plane. The pins jumper connections between both
sides of the board.
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ß The header strip between the two rows of diodes
connects to the pushbuttons on the box cover. The jumpers at the bottom assign a unique
code embedded in the transmitter’s signal.
Two capacitors flanking a voltage regulator are to the right.
One of two push-button clusters are à mounted on their own prototyping board and
screwed to the underside of the top cover.
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Circuit
description
This throttle uses a transmitter, receiver, and
other parts from LINX Systems.
These hybrid circuits are almost completely self-contained needing only an
antennae and power to transmit and receive a signal. Also, Be aware that there are several
chips similar to the encoder chip used here. Visit Reynolds Electronics
for several RF projects and parts.
Almost all of these parts are also available at DigiKey.
The encoder chip (IC-1) combines the status of
the eight switches (SW1 through SW8) and (D1 through D8) to a single signal
that leads to the transmitter. Diodes
(D9-D16) provide connect the rest of the circuit to the battery power. Resister network (R3) holds the inputs
each input low unless pulled high by the press of any button. This saves power when no button is
pressed. The remaining eight diodes pull a corresponding input of IC-1 low.
A 9-volt battery supplies about 7 volts under normal
loads. IC-2 further drops this to
the 5 volts required by the decoder while capacitor C1 prevents any
transient changes. This voltage
passes through each switch as it is pressed, then passes through a diode
(D9-D16) to a resister (R2) whose value is selected such that about 3 volts
to power the transmitter module (TX1).
Capacitor C2 again removes any transient changes of voltage.
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TRANSMITTER / CONTROL CIRCUIT
See specifications for part pinouts.
The four jumpers (J1 through J4) provide a unique
four-bit device address. Eight
jumpers would expand this to an eight-bit address for a possible 256 throttle
devices. There are also three
different frequencies available to provide control for over 750 trains
simultaneously.
See PARTS LIST
for transmitter for parts and additional information.
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OVERVIEW
OF RECEIVER AND THROTTLE CIRCUIT BOARD
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The board above is the other half of the wireless
throttle. The schematic below shows the receiver portion of this
circuit. It receives the signal and
splits it into individual channels to control the train speed, direction,
and auxiliary functions.
The receiver, like its transmitter à
counterpart, consists of the receiver module (RX1) and an antenna
(ANT). Note the ground plane visible
on the far side of the PC board.
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See specifications for part pinouts.
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Circuit
description
The antenna (ANT) provides a signal to the
receiver module (RX1) which in turn presents a data signal to the decoder
(IC-3). The decoder separates the
data into eight channels each of which connects to the input of one of the
eight Operational Amplifiers (IC1 and IC2).
Note that several similar decoders are available and operate in a
slightly different manner. One type
(A) presents a signal that appears as a train of square pulses when a high
signal is present at that channel.
The other type (B) changes with the level of the signal. Both will work by a simple change of
resister values in the personality module but here it the problem. If you are running a train using the type
(B) decoder, and for any reason the
signal is lost as in a weak battery, the throttle may be left in the
acceleration mode with the train speeding up to full speed.
Opto-isolator (IC-4) has four channels and
completely separates outputs meant for computer interface from any
circuitry of the throttle. Resister
networks (R8 and R9) limit the power and protect all the inputs and outputs
of the isolator from excessive current.
Two amplifiers lead to the throttles reversing
circuits. Three more lead directly
to opto-isolator (IC4) used to isolate the auxiliary computer signals. Two
more amplifiers lead to the personality module that controls the speed of a
train. Notice that the acceleration
amplifier is the one that uses the (+) input to (IC3). All other amplifiers use the (-)
lead. Also, note the direction of
the diodes leading to the personality module.
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The last amplifier leads both to the personality
module and to the fourth input of opto-isolator through the resister (R7)
and transistor (T1).
IC-5 further drops the 18 volts from the power
supply to the 5 volts required by the decoder. Capacitors C2 and C3 suppress any
transient changes. Resistors (R2)
and (R3) form a voltage divider that supplies 2.5 volts to one side of each
amplifier. The output of each
amplifier as the decoder’s signal passes this value.
The value of resister (R1) is such that it will
drop the five volts from (IC05) to about 3 volts. C1 prevents any transients of this
voltage.
The four jumpers (J1 through J4) provide 16
unique device addresses but as with the transmitter, using eight jumpers
will allow the control of 256 devices.
Three frequencies available expand this to a total of control over
750 trains simultaneously.
See PARTS LIST
for transmitter for parts and additional information.
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The personality module is a “surf board” or
Single-row In-line module (SIM) card.
Several cards, each with slightly different resisters, are easily
unplugged and interchanged allowing the rapid change of the how the
throttle performs.
It is, of course, possible to have one card for each
engine or for each operator.
Practical experience has show that is not necessary. A more reasonable approach is to have one
for very light engines, another for medium engines, and a third for double heading. A forth may be kept to virtually eliminate
any momentum effects.
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Remaining throttle circuits
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The transformer portion of this throttle is
elsewhere in a special fire-resistant cage along with the other
transformers that power the railroad.
The basic requirement is simply a transformer that will supply about
16 to 20 volts AC at an amp and a quarter.
I use one that provides 20 volt/amps (watts) of power.
See more on POWER
SUPPLIES.
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Looking near the right, middle of the schematic
above we see that power from the transformer connects to the main rectifier
shown here in the top center. The
large capacitor to the right raises and filters the DC to a more constant
22 volts with no load and about 18 volts while running a train. There is no further regulation for the
throttle power.
Mounting rectifier with the throttle circuitry
insures that crossed wires from the transformer will not cause any damage.
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The 470-µfd capacitor, above the rectifier in the
schematic, provides the momentum simulation of a train. The personality module increases or
decreases the charge (voltage) on this capacitor and in turn, this charge
is reference by the remaining parts of the throttle to determine the final
speed of the train.
Push-button throttles require a capacitor but the
size can be smaller. 470 µfd is
large enough to keep the train moving for half an hour before it coasts to
a stop.
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Conditioning,
in the context of this throttle, applies to the waveforms
used to improve the starting of a train. All four operational amplifiers of
(IC-U2) in the schematic are used superimpose just
enough of a DC pulsing current on the basic control signal from the
momentum section to smoothly start a train.
These pulses dwindle in magnitude as the train accelerates and
diminish to nothing ad a ‘cutout’ point once the train is moving. A LED is provided as a visual way to
monitor this pulse and cutout point
Four different adjustments modify the pulsing
current to match the characteristics of an engine.
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Circuit
description
All four operational amplifiers of IC-U2) shape
the control waveform. Amplifier D
measures, amplifies, the charge of the momentum capacitor and reduces the discharge
of the capacitor. (2) 100K resisters
tied to pin 12 improve the sensitivity of the amplifier.
Amplifier B produces a starting pulse using two
diodes, two 100k resistors and a 1M potentiometer. The arrangement of the diodes permit
varying the duty cycle of the pulse from 0 to 100% as the potentiometer’s
setting changes. The 2.2K resister
and 500K potentiometer nearby controls the magnitude of this signal from
Amplifier B and connects through a diode and 100k Resistor to amplifier
C. The diode holds this signal to a
half-wave AC and is mixes it with the signal from amplifier D.
Amplifier C mixes the signals from B and D to
form the composite waveform that powers and engine to a slow start.
Amplifier A controls the point at which the
starting pulse fades to pure DC as the engine increases speed. The throttle setting (capacitor charge)
from gate D, Pin 2, is compared to a desired set point through a 10K
potentiometer and a 10K resister.
The result connects through a 100K resister to pin 5 of gate B.
The 47K resister connected to amplifier A, the
2N3904 transistor, 1k Resister and the LED form a visual indication of when
the starting pulse is active.
For a discussion of propulsion power wave forms
and how they can affect the operation of a locomotive, click HERE
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Most circuitry in the throttle uses only tiny
amounts of current typically in the range of .001 amps or less. A typical engine can use anywhere from
.20 to .50 amps
The power amplifier in this project is simply a Darlington [power] transistor. This type of transistor is actually an
integrated circuit that contains more than one transistor to provide more
power than otherwise possible plus a bit of support circuitry to make the
device more rugged electronically.
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There are many alternate methods of boosting the
power to drive a train. DCC and
other circuits use SCRs instead of transistors. This has the advantage of required a much
smaller heat sink but at the penalty of being much harder on motors. Both voltage regulators and current
regulators can give a much more precise control of the voltage applied to
the rails however in my opinion the preciseness is wasted and only causes
other problems. These include the
complexity of the circuits with the added cost of the parts.
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The anti reverse control circuit insures that an
engine traveling at full speed in one direction can not be jammed into
reverse yet allow a slow moving switcher to immediately reverse over and
uncoupling ramp to “kick” a stubborn coupler apart. This protects the drive train of a
locomotive and the draft gear on cars.
One input of amplifiers C and D of IC-U1 connect
to a10K potentiometer, a 15k resister, and a 22k resister. This determines the voltage level at
which reverse locking takes place.
Reversing of trains will not occur once the track voltage exceeds
this level.
The other input connects through 100k resisters
to a direction signal, the train speed, and to a constant voltage. BOTH the train’s speed and either the
forward or reverse direction signal must be present to pull the input down
low enough for the amplifier to pass a signal to amplifier B.
The six resisters around amplifier B form a
“flip-flop” circuit that controls the direction of a train. It “remembers” whether amplifier C or D
last sent a signal and outputs a signal through the 15k resistor and
transistor to a relay. Amplifier A
simply reverses the output from B.
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The use of using Twin relays for reversing over
one has many advantages. A relay is
similar to a motor in that it requires a comparatively large amount of
current to operate and can cause spikes of current dangerous to solid-state
circuits. The main problem however is
that they also draw current that can drop the power supply voltage down a
tenth of an amp or so. While that
may not sound like much, using a single relay to control the direction of a
train can enough to cause a noticeable difference when running forward or
reverse.
Using two relays, with exactly on operating at
all times, insures a constant drain on the power supply, only half the
maximum current is used constantly, hence, much smaller relays can be
used.
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Each relay coil has a .47 µfd capacitor and diode
across it to dampen out the voltage spikes generated by any large inductive
load. The 150-ohm resister further
dampens these spikes.
The 10-µfd capacitor and 1K resister leading
through the contacts to the tracks suppress power surges from and to the
engines especially when they run over dirty track.
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Model Railroading is fun in Connecticut.
Bob Van Cleef, MMR
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