e99a050.pdf

GENERAL INTEREST

super loco decoder

EEDTS Pro

for use with virtually any make of locomotive

The super loco decoder (ESLD) described in this article provides a

worthwhile alternative for model railway enthusiasts who want to make

their locomotives digital at reasonable cost. One of the benefits of build-

ing it yourself is that the design can be adapted to virtually any make of

locomotive. Another is that the loco decoder provides several additional

facilities that complete

the digital control of

the model railway.

Brief specification

Suitable for two-rail and three-rail systems

Suitable for d.c. and a.c. motors

Four functions; one of which is suitable for use as a preset flashing light

Brightness of headlights presettable

Design by H J Prince

Frequency of flashing light presettable

Locomotive detection by infra-red LED

Storage of movement and function settings for indeterminate period in case

of power-down

INTRODUCTION

A glance at the brief specification

shows that the super loco decoder is

suitable for universal applications. It

may be used with virtually all current

model railway systems, since a large

number of functions may be selected at

will and to personal requirements.

Some of these are selected by software

via a personal computer and the con-

trol unit described in the June 1999

issue of this magazine. The decoder

may also be used as a stand-alone unit,

in which case the loco addresses are set

with the aid of a diode matrix. For this

purpose, 16 preprogrammed loco

addresses are stored in EEPROM.

145027 Motorola combination and con-

sists of nine trits . The transmitter

(145026) has nine inputs that recognize

three levels: high (10, low (0), and open

(x). This information is available in ser-

ial form at the output, so that the out-

put signal consists of nine trits. In the

Märklin system, four trits are used for

loco addressing, one for switching the

headlights (FO) on and off, and four

for the speed and direction of travel.

Each trit consists of two bits that

represent the three levels: 00; 01; 11,

that is, 0, x, and 1, respectively. This

gives a total of 18 bits—see Figure 1 .

In the old format, the function-0

bit and the data bits for speed are

used in binary form only. This means

that up to 2 4 =16 steps may be set:

one for standstill, one for reversing

the direction of travel, and 14 for the

speed. When the data bits are used in

trinary form, 3 4 =81 combinations are

possible. If this figure is reduced by

the 16 steps in the old format, 65

remain, more than sufficient to con-

trol new functions.

Space does not allow all the relevant

tables to be shown. Briefly, it comes

down to each trinary word of four trits

representing speed, direction of travel,

and the status of one of the function

outputs (on/off). All combinations are

stored in tabular form in the decoder

IC. Provided that they coincide with

the data sent by the Märklin con-

trollers, all actions will be performed

smoothly and error-free.

DESIGN

In all model railway designs, compact-

ness is a first requirement, and the

decoder therefore uses a Type

PIC16F84 microcontroller, IC 1 . This

Microdevice I/O controller provides 13

I/O connections, RAM, EPROM, and

EEPROM. Together with a small num-

ber of surface-mount devices (SMDs),

it is therefore eminently suitable for

building a complete and compact

decoder.

The circuit diagram of the decoder

OLD AND NEW FORMAT

To understand how it is possible to

obtain several new functions with the

current Motorola format, it is necessary

to reflect on the composition of the

original format.

In the original format, each data

word has its origin in the 145026/

Elektor Electronics

10/99

Compatible with old and new Märklin format

Loco address programmable via personal computer or diode matrix

Top speed presettable

Rate of acceleration and deceleration presettable

is shown in Figure 2 . Diodes D 1 –D 4 in a

bridge arrangement, make the polarity

of the track voltage independent of the

supply voltage

The supply voltage is applied to IC 1

via resistor R 5 and the base-emitter

junction of transistor T 1 . It is kept

steady by zener diode D 9 . When there

is track voltage available, a current

flows through the base-emitter junc-

tion of T 1 , so that the transistor is dri-

ven into saturation which makes pin 2

(RA3) of IC 1 high. In the absence of

track voltage, the potential across

capacitor C 3 drops below the zener

voltage (5.1 V), which causes T 1 to be

cut off, whereupon the input of IC 1

goes low. After a certain period of time,

the program executes a power-down

routine and writes the data as to speed,

direction of travel, and function infor-

mation into EEPROM.

The clock for IC 1 is provided by a

4-MHz ceramic resonator, X 1 . It may

also be by a small quartz crystal, but a

resonator is smaller and less expensive.

Moreover, when a resonator is used,

capacitors C 1 and C 2 may be omitted.

Track information is applied to an

interrupt input of IC 1 via resistor R 3 .

Outputs RB 1 –RB 7 control the head-

lights, four functions, and an infra-red

LED respectively. These function out-

puts, whose total current must not

exceed 1.5 A, are buffered by IC 2 .

Diodes D 5 –D 8 are optional; they

form a matrix that serves to set the

loco addresses when the decoder is

used as a stand-alone unit. Depending

on the number, placement and posi-

tion of the diodes they identify one of

the loco addresses in a table in EEP-

ROM. This makes it possible for 16

loco addresses to be set without the

aid of external software or electronic

circuitry. Each address in the table

may be reprogrammed, which will be

reverted to later.

If, in accordance with Table 1, a

diode is soldered in one of the posi-

tions marked ‘D’ on the PCB, the loco

address associated with that position is

actuated. A number of addresses are

used in the central control of the

Märklin system and these are therefore

easily set.

The engine control driver may be

adapted for use with d.c. or a.c.

motors. That for d.c. motors is shown

at the lefthand top of Figure 2. Dar-

lington transistors T 4 and T 5 , and resis-

tors R 9 and R 10 , are not needed when

Märklin series motors are used. The

two stator windings of these are linked

to terminals M 1 and M 2 , while the

common armature winding is con-

nected to terminal M 3 . Diodes D 10 and

D 11 are connected with

reverse polarity to

quench the counter-

e.m.f. of the motor:

their cathodes are

Table 1

Table 1. The loco

addresses may be set

with the aid of a diode

matrix.

loco no. loco address diode 5678

––––

–––D

––D–

posed on a carrier of about 38 kHz and

is received by a standard infra-red

decoder mounted adjacent to, or on,

the track. After the address has been

processed (also by a PIC), it is trans-

ferred to the EEDTS Pro control unit.

The same principle as in the return sig-

nallers in the EEDTS and Märklin S88

systems is used. This makes it possible

to determine train-dependent track

sections. This infra-red loco address

return signaller will be reverted to in

the next instalment.

The current through the infra-red

LED is limited by a 2.2 k

––DD

–D––

–D–D

–DD–

–DDD

D–––

D––D

D–D–

D–DD

DD––

series resis-

tor. It is clear that the value of this resis-

tor influences the maximum distance

at which the engine is detected by the

infra-red receiver. When the value is

1.0 k

DD–D

DDD–

DDDD

, the engine is detected at a dis-

tance of about one metre (just over

3 ft). The type of LED is immaterial:

dependent on its position and applica-

tion a 3 mm or 5 mm may be used.

linked to terminal M 3 .

When a standard d.c. motor is used,

T 4 , T 5 , R 9 , and R 10 are needed. The

motor is connected to terminals M 1

and M 2 . Bear in mind that the polarity

of the diodes is the opposite of that

when a Märklin series motor is used.

FIRMWARE *

The application in which the decoder

is used is not processor-friendly. Vary-

ing contacts of the wheels and tracks

cause frequent glitches and interrup-

tions in the supply voltage. Since this

creates a real risk of mishaps, it is nec-

essary to guarantee correct and unin-

terrupted execution of the program in

all circumstances. To this end, a num-

ber of important registers is tested reg-

ularly for consistent performance.

When something goes wrong, the pro-

gram is re-initialized and all registers

are reset. The program progression is

shown in Figure 3 : at the left the main

LOCO ADDRESS

RECOGNITION

As already stated in the first part of this

series of articles, it is essential for a reli-

able time table to know which train

enters a station and when. The present

loco decoder transmits a signal by

means of an infra-red LED (shown in

dashed lines at the right of Figure 2)

that has the same address as that set in

the decoder. This address is superim-

* Strictly speaking, firmware is system software held in read-only memory (ROM).

Figure 1. Representa-

tion of a trinary data

word.

Elektor Electronics

10/99

R10

D10

D11

M1 M2

ACCOMMON

1N4001

D10

D11

1N4001

BC857C

MJD6039

47µ

16V

R12

5V1

AC version

DC version

D 12

RA1

RA0

IR-LED

MCLR

RA0

RA1

RA0

270k

IC1

RB0

RB1

RB2

RB3

RB4

RB5

RB6

RB7

IR-LED

PIC16F84

IC2

RA2

RA3

ULN

2004

RA4

REV FUNCTION

FWR FUNCTION

OSC1

OSC2

GND

R11

4MHz

10µ

16V

Tant.

22p

990071 - 12

Figure 2. Circuit diagram of the

super loco decoder. Expanding

the section around T 2 and T 3 with

T 4 , T 5 , R 9 , R 10 (see top lefthand)

renders the decoder suitable for

operation with d.c. engines.

flow, and at the right that of the inter-

rupt routine.

A hardware reset results in a re-ini-

tialization of a number of configuration

registers in IC 1 . At power-down, the

relevant registers are stored in the EEP-

ROM. This is followed by the program

testing a number of registers whether

they have retained the correct setting.

If there is a discrepancy, the program

starts afresh and all registers are re-ini-

tialized.

Subsequently, the timers that pro-

vide regular processes, such as the F4

flashing rate, rate of acceleration and

deceleration, repetition time of the pul-

sating engine drive, and the dimming

of the headlights, are readjusted where

necessary. A wait loop determines the

flow time of the main loop and there-

fore the repetition time of the various

software timers.

At power-down, the settings of

speed, direction, and function then

current are written into the EEPROM,

but note that this applies only to those

registers that have been altered during

the operating period. This arrange-

ment prevents unnecessary writing

into the EEPROM every time the track

Start

Interrupt

Init

registers

IRled-

burst on

YES

Set

IR led

Set

Timer

Write speed and

function regs in

EEPROM

if not equal

Power

down

Y E S

Timer

interrupt

YES

Read

databit

YES

Timeout

Check

config regs

Raildata IRQ

Update bit counter

Update word counter

Shift bit in

Equal

YES

All

done

YES

Set timers

F4 timer

Velocity timer

IR burst timer

Powerdown timer

Compare data

Wait

Equal

YES

Setup

address

Ten

times

YES

Loco address

diode matrix

Speed

Look-up table

Calculate data

Loco address

Look-up table

Write setup regs in

EEPROM if not equal

Set speed and

function regs

Function

Look-up table

Figure 3. Program flow

of the loco decoder: at

the left, the main flow;

at the right, the inter-

rupt routine.

Set timer

Return int.

990071-13

Elektor Electronics

10/99

22p

AC-version

DC-version

990071-1

R11

IC1

FWR

REV

D10

IR-Led

Figure 4. Double-sided printed-circuit board for

the super loco decoder. The board has no provi-

sion for the infra-red LED and its series resistor.

Parts list

Resistors:

R 1 = 1.8 k Ω *

R 2 , R 5 , R 7 –R 11 = 10 k

voltage is interrupted. This lengthens

the life of the EEPROM appreciably.

Interrupt routines are started by a

leading or trailing edge of the data on

the rails of pin 6 of IC 1 or of the integral

hardware timer. Dependent on the

actual situation, all bits are clocked in

or the infra-red LED is driven. When

two data words are received, they are

compared with each other. If they are

identical, and the address is 79, a set-

up routine is started. Here again, writ-

ing to the EEPROM only takes place

when necessary. If the address is iden-

tical to the loco address, all data bits are

passed on and the various functions of

the decoder set.

the board, place the relevant SMD

component in the correct position and

heat the tinned pad again. When the

component sinks into the solder,

remove the soldering iron. Do not

move the component during the cool-

ing of the tin. When the tin has cooled

(blowing helps), solder the other ter-

minal of the component into place in a

similar manner. If necessary, re-heat

the first solder joint to make the tin

flow smoothly.

Solder all components in this man-

ner, starting, as always, with the pas-

sive ones and ending with the ICs. If

desired, IC 1 may be placed in a suitable

socket. Use one with turned pins.

However, if a socket is not used, the

finished board is significantly thinner

and this may be a great advantage in

smaller locomotives. Pay good atten-

tion to the polarity of diodes D 10 and

D 11 .

For the convenience of constructors,

the components side of the a.c. and d.c.

versions are shown

separately in Figure 4 .

Note that on the a.c.

R 3 = 270 k

R 4 = 270 Ω

R 6 = 47 k Ω

Capacitors:

C 1 , C 2 = 22 pF*

C 3 = 0.047 µF*

C 4 = 10 µF, 35 V*

C 5 = 47 µF, 10 V*

Semiconductors:

D 1 –D 4 , D 10 , D 11 = 1N4001*

D 5 –D 8 = LL4148*

D 9 = 5.1 V zener BZV55C*

D 12 = Infra-red LED LD261

T 1 = BC857C*

T 2 –T 5 = MJD6039*

Integrated circuits:

IC 1 = PIC16F84* (available pro-

grammed under Order No.

996523-1 —see Readers Services

toward the end of this issue)

IC 2 = ULN2004*

CONSTRUCTION

The decoder is best built on the dou-

ble-sided printed-circuit board shown

in Figure 4 . Building is not an easy job

for a beginner in electronic construc-

tion, since it involves surface-mount

components.

Using a soldering

iron with a small solder

tip, tin a single pad on

Miscellaneous:

X 1 = 4 MHz resonator (see text)

PC B Order no. 990071-1 (see Read-

ers Services toward the end of this

issue)

Figure 5. Auxiliary cir-

cuit intended for man-

ual adaptation of the

registers.

* Surface-mount version

20V

1N4001

BD560

Vdd

22k

8...16V

IC1

10k

145026

1N4001

GND

BC109

1N4001

GND

220µ

25V

8V2

100µ

16V

BD560

20V

220µ

25V

1N4001

990071-14

Elektor Electronics

10/99

Table 2. Programming

table for setting up the

decoder.

Table 2

Trit 98765

LLLL0

program loco address

MMM01

program maximum speed

AAA0X

program rate of acceleration/deceleration

version transistors T 4 and T 5 as well as

resistors R 9 and R 10 are not used, but

that two wire bridges are put in their

place. Connecting the motors has

already been described earlier.

In Märklin locomotives, the head-

lights and frontal signals are usually

interlinked at one side of the body of

the locomotive. This arrangement may

be kept for the present decoder. It

should be noted, however, that in the

case of two-rail operation the intensity

of the lights may be affected, depend-

ing on the polarity of the rails. It is,

therefore, better to supply the lamps

and other users connected to the func-

tion outputs from the +V terminal

(M 3 ).

Finally, note that no provision has

been made on the board for the infra-

red LED and associated resistor: these

should be mounted elsewhere. This

should, of course, be done in such a

manner that the diode points in the

direction of the infra-red decoder.

SSS11

program brightness of headlights

KKK1X

program flashing rate of function 4

loco addresses

data settings

LLLL

MMM

AAA

SSS

KKK

0000*

1111

000

0001

111X

001

000X

11X0

00X

0010

11X1

010

0011

11XX

011

001X

1X00

01X

00X0

1X01

OX0

00X1

1X0X

0X1

00XX

1X10

0XX

0100

1X11

100

0101

1X1X

101

010X

1XX0

10X

0110

1XX1

110

0111

1XXX

111

SETTING UP

Five registers have been reserved in

the EEPROM to set the following

functions: the loco address, the maxi-

mum speed, the rate of acceleration

and deceleration, the brightness of the

headlights, and the flashing rate of

function 4.

The registers are set by a combina-

tion of data bits at loco address 79.

Since this applies to all loco decoders,

make sure that there is only one loco-

motive on the track, otherwise all loco-

motives are programmed with the

same settings. Possible loco addresses

and data settings are shown in Table 2 .

When trit 5 is 0, a loco address will

be programmed according to data trits

6–9. When trit 5 is x (01) or 1 (11), the

other registers can be programmed:

which ones depend on trit 6. All this is

arranged by the EEDTS Pro software.

Where stand-alone working is

wanted, the registers may be adapted

with the aid of the auxiliary circuit

shown in Figure 5 . This is based on a

Motorola 145026 (transmitter) that is

permanently set to address 79. There is

no ready-made printed-circuit board

for the auxiliary circuit, so this will

have to be built on a small piece of pro-

totyping board or similar.

The data trits can be set with five

miniature 3-position switches in accor-

dance with the codes shown in Table 2.

When the push-button switch is

pressed, the data appear at the output

in serial form and the loco decoder is

programmed with the set value. When

the loco address is being set, the value

011X

X000

11X

01X0

X001

1X0

01X1

X00X

1X1

01XX

X010

1XX

0X00

X011

X00

0X01

X01X

X01

0X0X

X0X0

X0X

0X10

X0X1

X10

0X11

X0XX

X11

0X1X

X100

X1X

0XX0

X101

XX0

0XX1

X10X

XX1

0XXX

X110

XXX

1000

X111

1001

X11X

100X

X1X0

1010

X1X1

1011

X1XX

101X

XX00

10X0

XX01

10X1

XX0X

10XX

XX10

1100

XX11

1101

XX1X

110X

XXX0

1110

XXX1

XXXX*

*) cannot be set on Märklin equipment

in the loco table is superseded by that

set with the diode matrix. In principle,

it is, therefore, possible to supersede all

values in the table by soldering all

diode combinations once.

The decoder may be supplied by

the ±20 V line from the EEDTS booster

amplifier or by a mains adaptor with a

secondary alternating voltage of

8–16 V.

[990071]

Elektor Electronics

10/99

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