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.

 

A WIRELESS THROTTLE

 

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This handy motor board simulated a running engine motor and computer connection during the development and assembly of the throttle.  Using this gave a much more realistic and practical proof that everything worked the way it was supposed to and to make final adjustments before installation.  Note the LEDs to the right used to test the auxiliary computer connections.  

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    xxxa 

     

     

PARTS LISTS -   Almost all parts shown here may be obtained from Digi-Key

                               or second-sourced from other vendors.

    

Key

Source

Website

Description

D

DigiKey

http://www.digikey.com/

Source for almost all parts for this project

L

Linx Technologies

http://www.linxtechnologies.com/

Vendor of RF modules and parts

R

Reynolds Electronics

http://www.rentron.com/index.html

Source for RF parts and kits

J

Jameco

http://www.jameco.com/ 

Assorted bargain parts and tools

         

    

Handheld transmitter   

       

PART

Source

Source #

Description

Use

B1

D

N705-ND

9v NiMH rechargeable battery

Main power

IC-1

R

CIP-8E

20-pin 8-bit encoder

Channel selector

IC-2

D

78L05ACZNS-ND

5v @ 100ma voltage regulator TO-92

Low power regulator

ANT

D

ANT-315-HETH-ND

Coil Antenna

Transmit signal

TX-1

D

TXM-315-LC-ND

Transmitter Module

Form signal for transmission

C1

D

P969-ND

47 µfd @ 10v Capacitor

Filter

C2

D

P966-ND

10 µfd @ 10v capacitor

Filter

SW9

D

EG1901-ND

SPDT slide switch

Power on/off switch

D1-D16

D

1N014BCT-NT

Small switching diode DO-35

Isolation

R1

D

150QBK-ND

150 ohm @ 1/2w  carbon resister

Battery protection

R2

D

560EBK-ND

560 ohm @ 1/8w carbon film resister

Voltage Drop

R3

D

770-101-R100KP-ND

9 x 100k resister network, common bus

Pull down to zero

SW1-8

D

EG1821-ND

12mm square Tactile switch

Function control

SW1-8

D

EG1080-ND

Key Cap

See catalog for colors

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

J1-J4

D

 

Jumpers

Device selection code

     

    

Throttle (Receiver)   

           

ANT

D

ANT-315-HETH-ND

Coil Antenna

Receive signal

RX-1

D

RXM-315-LC-ND

LINX Receiver Module

Tune signal for decoder

IC-1,2

D

296-1391-5-ND

LM324 Quad Operational Amplifier

Condition signals from decoder

IC-3

R

CIP-8D

20-pin 8-bit decoder

Split signal into 8 channels

IC-4

D

160-1364-5-ND

LTV846 4-channel Opto-Isolator

Computer interface

IC-5

D

78L05ACZNS-ND

5v @ 100ma voltage regulator TO-92

Receiver power supply

C2

D

P4669-ND

.33 µfd  capacitor

voltage filter

C3

D

P969-ND

47 µfd  @ 16v capacitor

Voltage filter

C1

D

P966-ND

10 µfd @ 10v capacitor

Filter

C4

D

399-4264-ND

.1 µfd disk

Local transients

D1,2,3

D

1N014BCT-NT

1N014  Small signal diode  DO-35

Filter polarity

R1

D

330KEBK-NT

330 ohm @ 1/8w carbon film resister

Voltage drop

R2

D

470KEBK-NT

470K @ 1/6w carbon film resister

 

R3

D

68KEBK-NT

68K  @ 1/6w carbon film resister

 

R7

D

33KEBK-NT

33k   @ 1/6w carbon film resister

 

R8

D

62J2893

680 x 5 resister array

 

R9

D

32K9620

1.5K x 9 resister array

 

T1

D

2N3904FS-ND

2N3904 small signal NPN transistor

 

J1-J4

D

 

Jumpers

Device selection code

 

 

 

 

 

 

 

 

 

 

R4

D

The value of these parts will vary depending

On the running characteristics desired.

The following values are one possible combination

2.2K

15K

47K

Panic stop

R5

D

Service brake

R6

D

Acceleration

       

   

Throttle (Control)   

      

D-1

D

KBPC110-ND

3-amp Bridge Rectifier

Power Supply, DC

D-2,3

D

1N014BCT-NT

1N014  Small signal diode  DO-35

Pulse Generator

D5

D

1N014BCT-NT

1N014  Small signal diode  DO-35

Mix  Pulse strength

D-6,7

D

1N014BCT-NT

1N014  Small signal diode  DO-35

Reverse Lockout

D-8,9

D

1N014BCT-NT

1N014  Small signal diode  DO-35

Anti-surge, relay

C-1,2

D

P4671-ND

.47 µfd @ 50v Metallic Film Capacitor

Anti-surge, relay

C-3

D

P5169-ND

1000 µfd @ 35v Electrolytic capacitor

Power Supply, Filter

C-4

D

P5155-ND

470 µfd @ 16v  Electrolytic capacitor

Momentum

C-5

D

P4671-ND

.47 µfd @ 50v Metallic Film Capacitor

Pulse Timing  U2-B

C-6

D

P1280-ND

10 µfd bipolar capacitor

Spike suppression

U-1

D

296-1391-5-ND

LM324 Quad Operational Amplifier

Reversing Control

U-2

D

296-1391-5-ND

LM324 Quad Operational Amplifier

Wave Shaping

Q-1

D

2N3904FS-ND

2N3904 transistor

Adjust Cutoff point

Q-2,3

D

2N3904FS-ND

2N3904 transistor

Relay control

Q-4

D

497-2539-5-ND

TIP120  NPN Darlington transistor

Power amplifier

K-1,2

D

Z221-ND

12v @ 10amp  SPDT relay

Reversing control

LED-1

D

 

LED

Cutoff point adjust

R-1

D

10KEBK-NT

10k @ 1/8 carbon film register1

Cutoff adjust

R-2

D

U262R254B-ND

250K potentiometer     Violet

Frequency

R-3

D

U262R504B-ND

500K potentiometer     Brown

Strength

R-4

D

U262R105B-ND

1M potentiometer   Lt Blue

Duty cycle

R-5

D

U262R503B-ND

50K potentiometer    Orange

Reverse lock

R-6

D

U262R103B-ND

10K potentiometer       White

Cutoff point

R-7

D

1KEBK-NT

1k @ 1/8 w carbon film resister

Cutoff current limit, LED

R-8

D

150H-ND

150 ohm @ 1/2w  resister

Protection from relay coil

R-9

D

OF102JE-ND

1K @ 1/2w carbon resister

Protection from motor kickback

R-10

D

2.2KEBK-NT

2.2k @ 1/8 carbon film register1

Current limit, power transistor

R-11

D

22KEBK-NT

22k @ 1/8 carbon film resister

Reverse lock adjustment trim

R-12

D

47KEBK-NT

47k @ 1/8 carbon film resister

Feedback, direction flip-flop

R-13

D

47KEBK-NT

47k @ 1/8 carbon film resister

Current limit, cutoff

R-14

D

10MEBK-NT

10M @ 1/8 carbon film resister

Feedback, U2-A

R-15

D

15KEBK-NT

15k @ 1/8w carbon film resisters

Reverse lock adjustment trim

R-16,17

D

15KEBK-NT

15k @ 1/8w carbon film resisters

Current Limit, Direction op-amp

R-18,19

D

15KEBK-NT

15k @ 1/8w carbon film resisters

Current Limit, direction relay

R-20,21

D

100KEBK-NT

100K @ 1/8w carbon film resister

Voltage divider, U1-A

R-22,23

D

100KEBK-NT

100K @ 1/8w carbon film resister

Voltage divider, U1-B

R-24

D

100KEBK-NT

100K @ 1/8w carbon film resister

Bias, Reversing U1-B

R-25,26,27

,28,29,30,31

D

100KEBK-NT

100K @ 1/8w carbon film resister

Bias, direction U1-C and U1-D

R-32,33

D

100KEBK-NT

100K @ 1/8w carbon film resister

Pulse Generator

R-34,35

D

100KEBK-NT

100K @ 1/8w carbon film resister

Voltage Divider, Cutoff

R36

D

100KEBK-NT

100K @ 1/8w carbon film resister

Frequency Adjust trim

R-37,38

D

100KEBK-NT

100K @ 1/8w carbon film resister

Voltage Divider, U2-C

R-39

D

100KEBK-NT

100K @ 1/8w carbon film resister

Pulse Strength current limiter

R-40

D

100KEBK-NT

100K @ 1/8w carbon film resister

Speed current from U2-D

R-41,42

D

100KEBK-NT

100K @ 1/8w carbon film resister

Voltage Divider, U2-D

R-43

D

100KEBK-NT

100K @ 1/8w carbon film resister

Pulse strength trim

 

 

   

Miscellaneous

 

 

D

V1044-ND

Vector 8001 circboard pattern “D”

Project board

 

D

V1055-ND

Vector K24 Test pins

Optional or as required

 

D

A94120-ND

20-pin IC socket

IC-1

 

 

 

 

 

 

D

929974-01-36-ND

Sip female Header*

connect buttons to board

 

D

929834-02-36-ND

Sip male Header*

Jumpers, connections

 

D

S9003

Jumpers

Device addressing

 

D

S1122-36-ND

Right angle header*

Battery connection to charger

 

D

HS135-ND

Heat sink*

Power Amplifier Transistor

 

D

PC51-ND

Blank Copper Clad PC Board *

Transmit & receive modules

 

D

Various

Assorted #6 screws*, nuts and washers

 

 

*  modified

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xxxa    

    

           

   

FURTHER INFORMATION

 

Most vendors supply both pictures, specifications sheets that contain pinouts and electrical information on how to use a given part as shown in the following sample PDF files:

 

        CIPP-encoder/decoder chips 

        Linx  long range Receiver

        Linx  long range transmitter

        Reynolds RF Transmitter and Receiver

 

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xxxa      

     

   

The Linx Technologies family of modules includes matching radio frequency transmitters and receivers that are perfectly suitable for model railroad use along with antennas, evaluation kits and a number of support products.

 

These 3-volt hybrid modules are extremely rugged, easy to use, an excellent value for the price and designed specifically for battery power.

 

    

These modules use surface mounting technology for direct soldering to a PC board about the size of a TV remote control.  Linx specifications state that there should be a backplane surface or layer of copper cladding behind this circuit for optimum operation.  Reynolds Electronics uses Linx products in many of its products and sells these modules already mounted on a backplane along with several additional products used in these throttle circuits.

 

  

    

The only other component required to make a complete transmitter is the antenna.  Be sure to read the Linx specifications for the layout of the ground plane, Transmitter Module, and antenna.    A plain #22 wire cut to the right length works quite well in a normally sized train room but it is a bit crude.  Here are three other forms antennas that are common and easily used.

 

    

The traditional monopole external antenna will yield the maximum range of up to 3000 feet outside and about half that indoors.

 

 

  

    

This antenna mounts directly on the PC board like any other component and gives performance similar to a monopole.  It is a bit more directions however you will never know it in a train room

     

       

Wound Coil antennas do not quite have as much range as others but are very inexpensive and work extremely well in a train room.  Hint: do NOT bend or distort the coil in any way.  

 

     

           

This receiver daughter board shows the relationship of the antenna to the receiver module.  This board started as a blank double-clad PC board. The backside is blank behind the antenna and completely solid behind the receiver. 

 

Use a knife to cut the groves in the copper cladding to form the pads and traces as required and peel away the excess cladding.  Widen these groves a triangular file as required.

 

This process may be a bit slow and tedious compared to etching the design but is faster when only two or three parts are required and avoids using hazardous chemicals and everything that goes with them.          

 

 

 

 

    

Linx Technologies offers these self-contained evaluation boards to demonstrate how easy it is to interface additional components the transmitter and receiver modules.

 

 

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xxxa 

    

      

Propulsion Power Wave Forms

 

The most vexing problem in model railroad operation is the transition of a locomotive from a standing to a slow speed start.  A locomotive, all too often, will remain static as the throttle advances to a certain point and then suddenly jump to life.  Flywheels can help but there is not always room for one, especially in small locomotives.  Steam engines are especially prone to this situation because of the added friction of the running gear and side-rod motion.  The following explains several electrical solutions designed to overcome this problem. 

       

 

The diagram to the right shows the performance of a typical locomotive running on pure Direct Current (DC).  Note how the speed remains zero until it suddenly jumps to running speed.  This is true for all DC motors to one extent or other due to the unequal magnetic forces exerted on the stators as each passes the stationary permanent magnets of the motor.  A slight increase of voltage also causes a speed-up of the motor.  Once the motor is running, the speed becomes closer in proportion to the track voltage applied.

Modern motors have skewed stators and better magnets that surround the motor to reduce, but not eliminate, this effect.

 

 

     

 

Using the unfiltered alternating current (AC) of a Transformer converted to DC is better than pure DC as the uneven pulses of current tend to help the motor start turning.  The use of a full wave rectifier offers an improvement over pure DC that is slight but noticeable.  The only penalty is that the motor may run slightly warmer than pure DC

 

 

 

This circuit shows the result of using a half wave rectifier.  The spaces between the wave peaks give a stronger “kick” to get the motor started.  This yields much smoother operations at slow speeds and in addition helps by burnishing the rails and removing dirt from between the railhead and wheels of a locomotive.  All this however is at the penalty of generating noticeably more heat in the motor and a great deal of wear between the gears and drive train within a locomotive not.  Running an engine at normal speeds with this type of power also causes excessive heat and can damage the motor’s magnets.

  

 

   

Early Transistor throttles were a throwback to pure DC, operationally speaking and motors again had the same problem of overcoming slow starts.  Then, as time passed, small amounts of AC ripple injected into the DC again brought back improved starts.  Transistor throttles however can cause several problems when a locomotive hits a bit of dirt on the tracks. 

 

The first problem with transistors in throttle circuits occurs when they act to vary current to maintain a given voltage. Rapid fluctuations in voltages occur as dirt causes the contact between the rail and wheels is lost or regained.  The transistor in turn causes great changes in current that is strong enough to sometimes burn small pits in the railhead. Second, this same lost of contact works in reverse from the motor.   A motor can be a generator such that when the wheels again contact the railhead, high voltage spikes generated by the motor can damage the transistor.  Another problem can be the heat a transistor generates.  A transistor generates the most heat when “half on” or about a track voltage of six volts. 

 

The realism of the throttle and braking action involved overcome these drawbacks.

 

 

Silicon Controlled Rectifier (SCR) circuits add new factors into the equation of an ultimate throttle.  This waveform is either 0v or 12v with the widths of each wave varying from extremely narrow for a stationary engine to almost full width for top speed.  This is ideal as far as the electronics are concerned because the SCRs generate very little heat, thus almost no heat sinks are required.  A DCC system decoder presents this waveform to the engine’s motor.

 

 

Unfortunately, there are several drawbacks.  The inductive load of a motor coupled to the rapidly changing voltages at the edges of each square wave produce high spikes of voltage and current, especially on dirty track.  These spikes are quite damaging to the permanent magnet of any DC motor.  A good motor can last thirty years or more before the magnets wear out however this waveform destroys them in less than three.

 

This waveform also causes pitting of the railhead especially on dirty track thus aggravating an already problematic situation.

 

A complete SCR throttle

 

 

 

    

This chart represents the complex waveforms of a generic DCC system.  The actual voltage across the rails is a modified, 12-volt waveform with only (2) possible widths allowed and representing four bytes of digital information.   Two of these bytes select a device while the other two determine to what extent

 

The decoder of an engine translates speed information and using a series of pre-programmed tables, it then outputs a voltage such that the locomotive smoothly increases its speed at a constant rate as the throttle is advanced.

 

 

 

 

 

Note that within the first jump of speed the strength and frequency of an additional waveform modifies the waveform to improve the DC component of the motor voltage to provide a smooth start.

 

   

There is one further point to consider about the speed table of a DCC throttle.  The purpose of the table is to have the motor increase in speed in direct proportion to a potentiometer used to control speed.  Some throttles use simple pushbuttons and resisters to control the speed.  On this type of throttle, the effect of the speed table is irrelevant as the engineer simply pushes a button to increase of decrease a locomotive to the desired speed.

    

       

This throttle presents a varying amount of voltage to the tracks as in a common throttle but it has a special circuit to start an engine.  This replaces the complex programming of the receiver and the associated equipment and learning curve of DCC.  Control settings for the frequency, duty cycle, strength and the point at which it fades to pure DC all vary the waveform imposed on the pure DC control voltage. 

All waveforms are AC avoiding the problems inherent with a square wave circuit.  The push-button control and a personality module eliminate the need for any speed tables.

 

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Bob Van Cleef, MMR

Last update  08/03/2012