e012036.PDF

GENERAL INTEREST

Speed Controller

Duet (2)

part 2: construction, programming and the power units

Design by B. Stuurman

Part 1 presented an overview of the system. In part 2, we deal with the

construction of the SpeedControl unit, user programming with a PC (via

the RS232 interface) and ﬁnally the construction of the two power units:

SpeedPower 1 and SpeedPower 2.

Elektor Electronics

2/2001

GENERAL INTEREST

COMPONENTS LIST

+4-6V

red

D4 = high-efficiency-LED yellow

D5 = high-efficiency-LED green

D6,D7 = BAT85

T1,T5 = BC547

T2,T3,T4 = BC557

IC1 =ST62T60BB6, programmed,

order code 000070-41 (see Readers

Services-page)

R13

RxD

HOEK1

R12

TxD

Resistors:

R1,R4,R8,R13 = 10k Ω

R2 = 100k

R11

R10

Ω

R3,R7 = 2k Ω 2

R5,R6,R9-R12 = 1k

Ω

PWM

R15

BZ1

R14,R15 = 560 Ω

P1 = multiturn preset, vertical

mounting (e.g., Bourns 3386W)

R14

000070-1

Miscellaneous:

S1 = pushbutton, make contact

X1 = 4MHz quartz crystal

Bz 1 = AC buzzer

Ferrite suppressor coil

PCB:

- in combination with SpeedPower1:

order code 000070-5 ;

- in combination with SpeedPower2:

order code 000070-4

(see Readers Services-page).

F/B

HOEK3

Capacitors:

C1 = 220pF ceramic, lead pitch 2.5

C2 = 100 µ F 16V, radial

C3 = 100nF

C4,C5 = 18pF ceramic

Semiconductors:

D1 =zener diode 2V3

D2,D3 = high-efficiency-LED (3 mm)

SpeedControl

construction

needle inserted into the connection

for the reset signal at the IC socket.

Slowly increase the applied voltage.

The reset signal should remain Low

until around 3.7 V, where it should

immediately go High. From around

3.75 V onwards, it should track the

supply voltage. If this is all OK, you

Figure 4. SpeedControl printed circuit board

layout (scale 1:1)

The printed circuit board for the

SpeedControl unit is shown in Fig-

ure 4 . For economic reasons, this

board is only available in combina-

tion with one of the two SpeedPower

boards (see the Components List), so

the ﬁrst task is to saw apart the two

boards (if you so desire).

If you work calmly and carefully with

a ﬁne-tipped soldering iron and keep

to the components identified in the

Components List, you

shouldn’t have any prob-

lems assembling the cir-

cuit board. A servo exten-

sion cable that has been

cut in two can be used for

the connecting cable. It is

a good idea to fit a ferrite

toroidal core onto the

cable to the receiver, since

this will isolate the circuit

from high frequency sig-

nals from the receiver, and

the remaining length of

the cable will not degrade

signal reception.

When everything is fin-

ished, wait a bit before

placing the microcon-

troller in its socket. First

connect the SpeedControl

to an adjustable power

supply with a range of

0–6 V, and connect a volt-

meter between 0 V and a

Figure 5. Fully assembled SpeedControl unit.

2/2001

Elektor Electronics

GENERAL INTEREST

on until the voltage again drops

below the set-point value. In gen-

eral, the cutoff voltage is referenced

to the full-load battery voltage, for

which a value of 0.7 V per NiCd cell

is used (Sub-C, 1500–2000 mAh).

brake [parameter] The ‘brake’ com-

mand is intended for electric gliders

with folding propellers that are ﬁtted

with a SpeedPower 2 unit. As soon

as the control stick (or the trim) is set

to the ‘reverse’ position, the brake

FET is activated after a set time

delay. ‘Reverse’ to ‘forward’ always

has priority.

curve (linear) This switch command

alternates between a linear and an

exponential power curve. In the latter

case, the amount of power supplied

to the motor is a better match to the

position of the control stick.

beep (high) This sets the volume of

the beep to ‘loud’ or ‘soft’.

freq [parameter] (2 kHz) This allows

the frequency of the PWM signal to

be set to four different values.

fail [parameter] (1 s) The combina-

tion of this command and the ‘safe’

command forms the ‘fail-safe’ provi-

sion of the SpeedControl. The ‘fail’

command can be used to specify the

maximum interval allowed for receiv-

ing no pulses (or bad pulses) before

reducing the motor power to zero.

header

S OUT

S IN

GND

9-way sub-D socket (female) solder

connector; attach shell after assembly

Remove pin and enlarge hole to 1.4-mm

∅

D9-connector

000070 - 2 - 13

4-pin header, solder connections.

Finish with heat-shrink tubing.

Figure 6. RS232 cable for communicating with a PC.

can insert the microcontroller in its socket.

The ready-made circuit board for the Speed-

Control is shown in Figure 5 .

then restarted via Speed.ht.

In order to enter the programming

mode, you must set the trimpot to

the ‘program’ position and then

switch on the power while pressing

the pushbutton. The SpeedControl

unit will then announce itself with

the message ‘command?’ on the PC

monitor. Now you can enter com-

mands. If an incorrect command or

incorrect parameter is entered, a

beep is generated and a message

appears on the screen. You can exit

this situation by pressing the Escape

key. If you type the command ‘?’ fol-

lowed by the Enter key, the com-

mand set is displayed as illustrated

in Figure 7 . Only lower-case letters

may be used for entering commands.

If the parameter is omitted, the cur-

rently active setting is displayed.

Programming

Before going any further, it’s helpful if you

ﬁrst match the SpeedControl to the transmit-

ter using the three-point timing setup, and in

particular the setup described in Example 2

of the first part of this article. Once this has

been done, you can test the operation of the

‘forw/back’ output.

After this test, the receiver and the Speed-

Control can be switched off. Set trimpot P1 to

the ‘speed’ position and hold the pushbutton

down while switching on the power. Now

you can test the operation of the trimpot. Its

behaviour should be essentially the same as

that of the control stick of the transmitter.

If no programming has been carried out,

default values are used. The microcontroller

copies these value from the ROM to the EEP-

ROM when it is first started up. A ‘virgin’

EEPROM cell contains either 00h or FFh.

After the values have been copied, the ‘test

cell’ contains 08h, so the program knows that

the EEPROM has already been written. In the

descriptions of the commands, the default

values are shown in parentheses.

A special cable is needed to allow the Speed-

Control to communicate with a PC. The

schematic of this cable is shown in Figure 6 .

The three loopback connections trick the

RS232 interface into being able to function

with only three leads (‘gnd’, ‘in’ and ‘out’). In

addition, you will need a terminal emulator,

such as the Windows accessory HyperTermi-

nal program. If you don’t use Windows, an

‘old-timer’ communications program, such as

ProComm, is perfectly usable. Set the proto-

col parameters to 19200 baud, 7 data bits, no

parity and 2 stop bits. With HyperTerminal,

you can save these settings on the desktop

under the name ‘Speed.ht’ (for example). In

our case, the new settings took effect only

after HyperTerminal had been stopped and

Commands

reptest (on) This switch command

enables or disables testing the repe-

tition interval (pulse rate). Disable

this test only if the repetition inter-

val of the transmitter is highly unsta-

ble. Note that this command dis-

ables the test, so to restore the orig-

inal setting, the command must be

issued twice. This applies to all

switch commands!

cutoff [parameter] This command is

used to set or disable the cutoff volt-

age. This is indispensable if the sup-

ply voltage for the receiver, servos

and SpeedControl is taken from the

BEC of a power unit, so that there is

no separate battery for the receiver.

When the supply voltage drops

below the set-point value, the motor

voltage is switched off. The power

supply to the motor can be restored

by putting the control stick in the

neutral position, and it will remain

Figure 7. The SpeedControl

command set.

Elektor Electronics

2/2001

GENERAL INTEREST

safe (resume) The options for this

command are ‘resume’ and ‘go neu-

tral’. If the motor power has been set

to zero in response to a ‘fail’ condi-

tion and the ‘resume’ option is

selected, normal operation will be

resumed as soon as control pulses

are again received. If the ‘go neutral’

option is selected, the control stick

must ﬁrst be set to the neutral posi-

tion before normal operation is

resumed.

log (off) If ‘log’ is active, bad pulses

are recorded in the ‘logbook’. This is

a 16-bit counter that provides an

indication of the reliability of the link.

The logging function costs a lot of

extra time in the controller, so it

should normally be disabled.

IC3

L4940V5

+5V

BEC

+7V2 / 12V

100n

10µ

100n

16V

Re1

re1

STPS

3045CT

Re2

47µ

16V

BAT

re2

–M

IC1

IC2

470 Ω

PWM

470 Ω

F/B

680 Ω

BC547

IRL2203N

HCPL2630

TC4426CPA

22n

BE C

0 V

Diagnostic commands

000070 - 2 - 15

Figure 8. Schematic diagram of the SpeedPower 1.

wd (on) This can be used to enable

or disable the digital microcon-

troller’s watchdog timer. If the

watchdog times out, the microcon-

troller is reset. When the watchdog

is disabled, the command processor

in the main program loop is enabled

and we can examine all memory

locations in the microcontroller and

modify them as desired.

mem [parameter] (off) This com-

mand, followed by a hexadecimal

address, causes the content of the

selected memory location to be dis-

played on the screen, updated

approximately three times per sec-

ond (exit with the Escape key).

put [parameter] The parameter byte

is written to the memory location

speciﬁed by the ‘mem’ command.

SpeedPower 1

The schematic diagram of the SpeedPower 1

unit, which has forward/reverse capability, is

shown in Figure 8 . The 5-V voltage regulator

(IC3), which also supplies power to the BEC,

is a low-drop type that can supply 1.5 A. With

page [parameter] 0 = EEPROM

page 0, 1 = EEPROM page 1, 2 =

RAM page 2.

The diagnostic commands can be

used to restore the default values.

This is done as follows. First enter

‘mem 00’ to select memory address

00h. Next, enter ‘page 0’ to select

EEPROM page 0, and then enter ‘put

00’ to write the byte 00h to that

address. Complete each entry with

the Enter key. When the SpeedCon-

trol is again switched on, the default

values will again be written to the

EEPROM.

GAT2

000070-3

HOEK3

IC3

+7,2V / 12V

BEC 5V

M+

PWM

F/B

RE1

M-

BEC 0V

RE2

HOEK1

GAT1

COMPONENTNS LIST

SpeedPower 1

Semiconductors:

D1 = STPS3045CT

D2 = BAT85

T1 = BC547

T2,T3 = IRL2203N

IC1 = HCPL2630

IC2 = TC4426CPA

IC3 = L4940V5

Resistors:

R1 = 680 Ω

R2,R3 = 470

Ω

R4,R5 = 2k Ω 2

R6 = 1

Ω

R7 = 100k Ω

R8 = 15

Miscellaneous:

Re1, Re2 = relay, Fujitsu 51ND06-N

(Conrad Electronics #505099-11)

PC1-PC9 = solder pin

PCB, order code 000070-5 (in

combination with SpeedControl –

see Readers Services page)

Ω

Capacitors:

C1 = 10µF 16V radial

C2,C3 = 100nF

C4 = 47µF 16V radial

C5 = 22nF

Figure 9. Printed circuit board layout for the

SpeedPower 1.

2/2001

Elektor Electronics

GENERAL INTEREST

two standard servos, the average current

consumption from the BEC is around 150 to

250 mA, but if reception is lost and the servos

start to jitter, the current consumption can

rise to as much as 1.2 A, and the receiver

must continue to work reliably under these

conditions. The PWM and ‘for/back’ signals

are electrically isolated by a dual digital opto-

coupler (IC1). IC2 is a dual inverting driver for

power MOSFETs. Each output can source or

sink 1.5 A, and the voltage can range from 0 V

on the ground lead (pin 3) to the supply volt-

age (pin 6). The inputs are TTL compatible.

One driver output (pin 7) is used to control

two power MOSFETs wired in parallel (T2 &

T3), while the other output controls a switch-

ing transistor (T1) that activates the relay. A

pair of Schottky diodes in a dual package is

connected across the MOSFET outputs to

handle ﬂyback currents, along with the ‘snub-

ber’ network (R8 & C5) that protects the

MOSFETs. The circuit is designed such that

the motor cannot run in the absence of an

input signal.

Figure 9 shows the printed circuit board for

the SpeedPower 1. This is supplied in combi-

nation with the SpeedControl circuit board,

and it can be separated from the latter board

if desired. The same remarks apply to the

assembly of this board as for the SpeedPower

board. The current-carrying tracks are laid

out extra wide, and if necessary they can be

IC3

L4940V5

+5V

BEC

+7V2 / 12V

+ M

47µ

16V

100n

4V7

R11

100n

STPS

3045CT

MTP50P03HDL

–M

547

BAT85

IC1

IC2

470 Ω

PWM

R10

470 Ω

F/B

BAT85

IRL2203N

HCPL2630

TC4428CPA

47µ

16V

22n

BE C

000070 - 2 - 16

Figure 10. Schematic diagram of the SpeedPower 2.

electrically ‘beefed up’ by soldering

lengths of copper wire on top.

Finally, fasten the interconnecting

cables and BEC cable. If the distance

between the power unit and the

receiver is greater than 20 cm, it is a

good idea to ﬁt a ferrite toroidal core

on the BEC cable, close to the

receiver.

the SpeedPower 1 unit; it has an

inverting and a non-inverting stage.

When ‘for/back’ is not active, output

pin 6 of the optocoupler (IC1) is

High, which blocks diode D1. The

‘PWM’ signal reaches the non-invert-

ing driver, which controls the power

MOSFETs, via the inverting driver

and diode D2. When ‘for/back’ is

active, output pin 6 of the optocou-

pler is Low, so that diode D1 con-

ducts. Input pin 4 of the optocoupler

remains Low, and consequently also

the gates of T2 and T3.

The base of T3 is connected to a

ﬁxed voltage of 3 V. When ‘for/back’ is

Low, the emitter of T1 is connected

M+

M-

SpeedPower 2

HOEK2

R10

BEC 5V

Figure 10 shows the schematic dia-

gram of the SpeedPower 2 unit,

which includes a brake FET. The

power MOSFET driver IC2 is a dif-

ferent type than the driver used in

PW M

F/B

000070-2

R11

BEC 0V

HOEK4

IC3

COMPONENTS LIST

SpeedPower 2

Semiconductors:

D1,D2 = BAT85

D3 = zener diode 4V7

D4 = STPS3045CT

T1 = BC547

T2 = MTP50P03HDL

T3,T4 = IRL2203N

IC1 = HCPL2630

IC2 = TC4428CPA

IC3 = L4940V5

Resistors:

R1,R2,R3 = 470 Ω

R4 = 330

Ω

R5,R6 = 2k Ω 2

R7 = 39

Ω

R8,R11 = 1 Ω

R9 = 560

Ω

R10 = 15 Ω

Miscellaneous:

PC1-PC9 = solder pin

PCB, order code 000070-4 (in

combination with SpeedControl –

see Readers Services page)

Capacitors:

C1,C4 = 100nF

C2,C5 = 47µF 16V radial

C3 = 22nF

Figure 11. Printed circuit board layout for the

SpeedPower 2.

Elektor Electronics

2/2001

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