e021050.pdf

GENERAL INTEREST

Lighting and

Gearbox Control

for remote-control model lorries

Design by D. Dzida

The circuit described here uses a PIC microcontroller to take over the

complete control of the lighting and gearbox in a model lorry. It can also

be used with a fork-lift truck, excavator or similar type of vehicle.

Elektor Electronics

1/2002

GENERAL INTEREST

The problem with these kinds of remotely

controlled vehicles is that they have a large

number of functions, which normally means

that an expensive remote-control unit must

be used. The project presented here consists

of a small printed circuit board, featuring a

microcontroller from the popular Microchip

PIC family, which looks after the extended

functions. This involves a combination of

automatic function control and the decoding of

supplementary functions.

Technical data

Supply voltage:

5V (from receiver)

Current consumption:

less than 10 mA

(excluding lamp currents)

External supply voltage:

5–12V

Blinking rate:

ﬁxed, approx. 0.5 Hz

Gearbox servo travel:

adjustable using a trimpot

Trailer coupling servo direction of rotation:

selectable (left/right) using JP1

Maximum current per output:

0.3 A

Keyed output for control only (max. 10 mA)

Relays may be connected (only with ﬂyback diodes!)

The automatic functions are:

– turn indicators are automatically activated

when the vehicle is turned;

– the brake lights go on when the accelerator

is released;

Note regarding the maximum lamp current:

If the lamps are powered from the internal supply voltage (see Figure 5) using the

receiver–speed controller BEC, the maximum output current of the speed con-

troller BEC must not be exceeded!

+5V

R10

100 Ω

D 6

D 5

D 4

D 9

D 8

SERVO

K12

DRIVE

R11

(RECVR)

GEAR

+5V

R23

1k2

R24

1k2

R25

1k2

R26

1k2

R27

1k2

R28

1k2

R12

100 Ω

SERVO

TRAILER

COUPLING

100n

R22

(RECVR)

R13

TRAILER

COUPLING

RC7

RC6

RC5

RC4

RC3

RC2

RC1

RC0

MCLR

K13

IC2

(RECVR)

R14

MDX

HEADLIGHTS

IC1

BC817

+5V

RA0

RA1

RA2

RA3

(RECVR)

R15

KEY /

SWITCH

CHANNEL

RB7

D 1

D 2

4051

RB6

PIC16C57

RB5

RB4

(RECVR)

+5V

R16

RB3

HAZARD

FLASHER

RB2

TOCKI

RB1

R19

RB0

R29

1k2

R30

1k2

R31

1k2

OSC1

OSC2

SERVO

R21

R20

CONTROL

JP1

(RECVR)

TURN

INDICATOR

R17

22p

16MHz

L / R

K14

10k

STEERING

R32

100 Ω

R33

100 Ω

BC817

K10

D1 0

MOTOR

CONTROL

+5V

R34

R35

100n

OUT

K11

(RECVR)

THROTTLE /

BRAKE

MOTOR

CONTROL

IC1

D11

D12

R18

10 µ

16V

010204 - 11

Figure 1. Schematic diagram of the lighting and gearbox controller. The microcontroller evaluates the pulse signals from the remote

control receiver and generates the additional control signals for the lights and gearbox.

1/2002

Elektor Electronics

GENERAL INTEREST

BEC

The acronym ‘BEC’ simply stands for ‘bat-

tery eliminator circuit’. This is a circuit that

eliminates the need for a separate battery to

power the remote control by providing an

adequately processed (stabilised and decou-

pled) supply voltage from the motor battery

pack. In a model lorry, this BEC is built into

the speed controller (the motor controller

for the tractor). Such speed controllers

always include a BEC with a 5-V output volt-

age. In the case of special regulators for lor-

ries, this 5-V output can supply a heavier

load than a normal regulator for cars. The

amount of output current that can be sup-

plied by the regulator depends on the model

and ranges from 1 to 3 ampères.

HOEK1

010204-1

K10

R10

R11

R12

R13

R14

R22

K12

R23

R24

R25

R26

IC1

R15

R16

R17

R27

R28

R29

R30

R31

K13

IC2

R18

K14

JP1

R32

D10

R33

HOEK3

D11

R34

R35

D12

K11

– the back-up lights go on when the vehicle

moves in reverse.

Supplementary switches on the remote con-

trol unit can be used to switch on the dipped

beams, main beams, hazard ﬂasher, ﬂashing

lights on the driver’s cab, horn and additional

output channels.

Figure 2. Printed circuit board track layout and component layouts for the copper

and component sides of the single-sided circuit board.

Lamp current

The current consumption of the circuit with

no lamps connected is less than 10 mA. Each

of the nine outputs connected to the transis-

tors can switch a maximum of 300 mA,

which altogether yields (9

Furthermore, the gearbox servo

can be sequentially shifted up or

down using a switch or the control

stick (just like a real Porsche, but

with only three gears…).

Finally, there is a trailer function,

0.3 A) = 2.7 A!

This amount of current can only be provided

by an external power source (wired as

shown in Figure 6).

If the internal 5-V supply voltage is used

(wired as shown in Figure 5), the 5-V output

of the vehicle’s speed controller must supply

not only the current for the remote control

receiver and the servos, but also the total

lamp current. Consequently, if there are

many lamps, a speed controller that can pro-

vide 1.5 A or more should be used. The fol-

lowing is a suggestion for the lamp selection

(5 V / 40 mA lamps):

dipped beams:

6 ×

40 mA

240 mA

main beams:

80 mA

160 mA

brake lights:

4 ×

40 mA

160 mA

back-up lights:

40 mA

80 mA

blinkers:

6 ×

40 mA

240 mA

hazard ﬂashers:

40 mA

80 mA

switched channel:

1 ×

80 mA

—————————————————–—————–

Total lamp current:

1.04 A

Figure 3. Top view of the prototype circuit board.

Elektor Electronics

1/2002

GENERAL INTEREST

K5, K6, K7, K9 and K11, respectively. From

there, they reach inputs X0–X6 of the multi-

plexer (IC1), and from the multiplexer they

arrive at port pins RA0–RA3 of the PIC micro-

controller (IC2). The 4051 CMOS multiplexer

could in principle be omitted, but then a

larger and more expensive PIC would be

needed.

The signals for the functions that are

directly controlled by the remote controller

(motor and steering) are not only passed on

to the microcontroller, but are also looped

directly through to output pin headers for

connection to the steering servo (K8) and the

motor speed controller (K10).

Port pin RB0 of the microcontroller is con-

nected to jumper JP1. This jumper selects the

direction of rotation of the servo for the trailer

coupling. The amount of travel of the gear

servo can be set using trimpot P1, which is

connected to port pin RB1.

By programmed processing of the various

input signals, the microcontroller generates

control signals for two servo outputs (K1:

gearbox servo and K3: trailer coupling servo)

and eleven switched outputs that are avail-

able on pin headers K12, K13 and K14. Nine

switched outputs are implemented as open-

collector outputs using external transistors

(T1–T9), while two output pins (of K14) are

directly connected to port pins RC3 and RC4.

Table 1 presents a summary of the connec-

tors with their designations and functions. If

you are interested in the software that

processes the signals in the PIC microcon-

troller, you can download it from the Free

Downloads page on the Elektor Electronics

website.

Each of the switched outputs is provided

with a LED that indicates the output state

(D1–D9 and D11). LED D10 has a special

function. After the supply voltage is

switched on, some of the signals from the

microcontroller are first calibrated (such as

the signals for the turn indicators, brake

lights and back-up lights). The control stick

must not be moved while this is happening.

LED D10 is illuminated only after the initial-

isation has been successfully completed

(which can take up to four seconds) in order

to indicate that the circuit is ready to be

used. LED D12 is connected to a switched

channel that is not currently used (K14/3)

and thus does not presently have any func-

tion. However, the author intends to use this

output to support an infrared link between

the tractor and the trailer.

COMPONENTS LIST

D10 = LED, 3mm, green, high

efficiency (low current)

T1-T9 = BC817

IC1 = 4051 SMD

IC2 = PIC16C57, programmed,

order code 010204-41

Resistors:

R1-R9,R20,R34,R35 = 2k

R10,R12,R21,R32,R33 = 100 Ω

R11,R13-R19,R22 = 10k

R23-R31 = 1k Ω 2

P1 = 10-turn preset, horizontal

mounting

Miscellaneous:

JP1 = 2-way pinheader with jumper

K2,K4-K7,K9,K11 = servo connection

cable

K1,K3,K8,K10 = 3-way pinheader

K12,K13,K14 = 5-way pinheader

X1 = 16MHz quartz crystal

PCB, order code 010204-1

Disk, project source code ﬁles, order

code 010204-11

Capacitors:

C1,C2 = 22pF

C3,C5 = 100nF

C4 = 10 µ F 16V radial

Semiconductors:

D1-D9,D11,D12 = LED, 3mm, red,

high efficiency (low current)

in which a single servo operates the

coupling to the tractor and the asso-

ciated support legs on the trailer.

This double function is specially

designed to be used with a Tamiya

lorry trailer kit. If only the trailer cou-

pling is needed, this function can

naturally also be used with other

model lorries.

updates or extensions. The circuit,

which is shown in schematic form in

Figure 1, assumes the use of a bat-

tery eliminator circuit (BEC) provid-

ing a regulated supply voltage of 5 V.

The microcontroller evaluates the

signals from seven output channels

of the remote-control receiver. At

each of these outputs, the receiver

provides the well-known pulse-

width modulated signal whose pulse

width ranges from 1 to 2 ms (1.5 ms ±

0.5 ms). These signals, which control

the gearbox, dipped/high beam,

switched channel, hazard flasher,

steering and motor (‘gas’) functions,

are connected to pin headers K2, K4,

Circuit operation

The heart of the controller is a

Microchip PIC16C57 clocked at

16 MHz. The version in the DIL28

package is used, since this makes it

easier to carry out possible software

Construction and use

Fitting the components to the printed circuit

board (Figure 2) requires some special atten-

Figure 4. The SMD components are ﬁtted on the bottom side of the circuit board.

1/2002

Elektor Electronics

GENERAL INTEREST

Table 1. Summary of connections

and functions

K12'

La1

La2

La3

Gearbox: K1 & K2

K1: Gearbox servo connection (only for a 3-speed gearbox)

K2:

La4

Connection for the cable from the receiver ‘gearbox’ output.

Function on the remote control unit: rocker switch with three positions:

up / off / down

La5

K13'

La6

Function:

The amount of servo travel to the left or right of the middle position can be set

using P1. Any change in the setting of P1 becomes effective only after the power

is next switched on. When the power is switched on, the servo always moves to

the middle position (second gear).

La7

La8

K14'

La9

• rocker switch ‘up’ once

servo moves forward

one position (e.g. from second gear to third

gear).

• rocker switch ‘down’ once servo moves

backward one position (e.g. from second gear to

ﬁrst gear).

1 st gear

3 rd gear

010204 - 12

2 nd gear

010204 - 14

Figure 5. Lamp connections when using the

internal supply voltage.

Trailer coupling: K3 & K4

K3: Connection for the trailer coupling servo (for a Tamiya lorry with electrically

operated support legs – see text)

K12'

K4:

Connection for the cable from the receiver ‘trailer coupling’ output.

Function on the remote control unit: rocker switch with three positions:

up / off / down

La1

La2

Function:

• rocker switch ‘up’ servo moves to position 1 (in this position, the support

legs are lowered until a limit switch on the trailer is tripped).

• rocker switch ‘off’

La3

La4

servo moves to position 3 (if the back-up light is not on,

the coupling cannot be opened!).

• rocker switch moved to ‘down’ AND back-up lights ON servo moves to

position 2 (in this position, the support legs are lowered until a limit switch on

the trailer is tripped).

After the rocker switch has been released (it

returns automatically to the middle position),

the servo moves to position 4. The trailer

coupling is now open and the tractor can sep-

arate from the trailer. The trailer coupling

remains open until the switch is again moved

to the ‘up’ position (to raise the support legs

and close the trailer coupling).

La5

K13'

La6

BT1

La7

La8

K14'

La9

Pos 4

Pos 1

Pos 2

Pos 3

010204 - 15

010204 - 13

Dipped beam / main beam: K5

K5: Connection for the cable from the receiver ‘dipped beam / main beam’ output.

Function on the remote control unit: toggle switch with three positions:

up / off / down

Figure 6. Lamp connections when using an

external voltage source (5–12 V).

Function:

• toggle switch set to ‘up’ all lights out (K12/3&4)

•toggle switch ‘off’

tion. Although the circuit board is single-

sided, components are mounted on both

sides. IC1 (a 4051 in an SMD package) is sol-

dered to the copper side. Particular care is

necessary in ﬁtting transistors T1–T9, which

are also mounted on the copper side. For ﬁt-

ting the components on the component side,

it is best to start with the wire bridges.

Attentive readers will probably notice that

dipped beam on (K12/3)

• toggle switch ‘down’

dipped beam and main beam on (K12/3&4)

Switched / keyed channel: K6

K6:

Connection for the cable from the receiver ‘ switched/keyed channel ’ output.

Function on the remote control unit: rocker switch with three positions:

up / off / down

Elektor Electronics

1/2002

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