A wireless transistorized throttle control system for model trains and railroad compatible with computerized railroad CPU control
A hand-held throttle unit is shown this is not a DCC system




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Handheld Transmitter


Remaining Circuits

       Power Supply

       Personality Module 

       Momentum Capacitor

       Wave Shaping

       Power Amplifier






      Test Motor

      Part Lists for Throttle

      Linx RF Parts

      Wave Forms




  Part Info, Pinouts, Specs etc.




           Meters etc.

Prototyping Circuits

           Bench Top Power Supplies













This old-time 0-8-0 switcher has a booster truck under the tender for low speed switching. The scratch-built wooden hopper behind is actually a 1940's WW-II product to conserve steel.

A local switcher starts the day at Bobston


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.



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.



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.   


This scratch-built computer operated the block system for the North River Railway.  the 8051-based CPU can access up to 128K internal RAM and is interfaced to 256 lines of I/O.  The computer features a LCD readout, photo cells train detection, Stall motor switch machines.  Note the RS-232 interface for program downloads.

Computer for controlled block system


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:

§  Range of 300’ indoors using internal antennas - 1000’ with external.

§  Over 750 control channels possible

§  Personality modules to customize characteristics for engineers or  types of engine(s) with simple plug-in

§  No decoders or other modifications required to engines.  Will run both unmodified and DCC/DC modified engines

§  Will not harm brushless or permanent magnet DC motors

§  Simplified computer compatible interface for Accessory control

§  Anti-reverse lockout protection at running speeds to prevent jamming of gears.

§  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


a generic transistor throttle dissected into it functional parts. 



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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Hand-held throttle for model railroad train control features internal antenna, and rechargeable batteries.  The controls are for speed, direction and auxiliary functions.




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


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. 



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.


¬  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     ŕ mounted on their own prototyping board and screwed to the underside of the top cover.  



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.







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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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 ŕ           

counterpart, consists of  the receiver module (RX1) and an antenna (ANT).  Note the ground plane visible on the far side of the PC board.



See specifications for part pinouts.



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.




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   







This power transformer is for the cab throttle described in this article for model railroad train control.


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.  

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. 





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. 


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.


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.



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. 



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

Last update   7/26/2012