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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. Most 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 gray 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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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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