DS-SCX18.S - DESIGNER SYSTEMS

CNTRL15.03.13 Revision 1.01

Designer

Systems

.co.uk

PRODUCT DESIGN AND MANUFACTURING

18 Channel Servo Driver Shield

for Arduino™ and Raspberry-PI™

Technical Data

Features

 ArduinoTM UNO Shield

standard form factor for

simple integration into any

Arduino project

 Frees up the ArduinoTM IO

lines normally used for servo

control

 I2C interface for simple con-

nection to Arduino or Rasp-

berry-PI

 Dual on-board 5Volt 3Amp

regulators, with heatsinking,

for servo power with enable

jumpers

 Sixteen (16) level speed con-

trol for each servo

 Movement complete and

soft-start complete status for

each servo

 Global activation control

ensures all servos start mov-

ing together, important for

multi-legged robots

 I2C address links allow up to

four [4] shields to be used

together to provide up to 72

servos

 LVD, RoHS and WEEE

compliant product

Description

The Designer Systems DS-

SCX18.S is an eighteen [18] chan-

nel RC servo driver with advanced

servo control features.

Specifically targeted at the Ar-

duino UNO board user [all other

Arduino boards supported] and the

Raspberry-PI the SCX18.S fea-

tures high speed I2C communica-

tion for easy project integration

and smooth speed control.

Once connected each servo can be

positioned (with speed control),

enabled, reversed and soft-started

by simply writing a value to an

internal register over the connect-

ed I2C interface.

The SCX18.S caters for the major-

ity of servos by providing a wide

pulse width range of 0.50mS to

2.50mS with 8uS per step accura-

cy and also provides global activa-

tion of new servo position, soft-

start & movement complete regis-

ters for superior control.

The SCX18.S provides dual high

power regulators capable of sup-

plying 5V @ 3A to the connected

servos from an external Li-Pol or

Ni-MH battery pack of 7.2 to 8.4V

and features a disable link to allow

the use of low voltage battery

packs of 3.6 to 4.8V.

The on-board I2C pull-ups are

jumper configurable to allow dis-

connection when connecting to the

Raspberry-PI, which has its own

pull-ups.

Applications

The SCX18.S has applications

in robotics, including quadru-

ped, hexapod and octopod ro-

bots, process control & sensor

manipulation when used in con-

junction with standard RC ser-

vos.

Selection Guide

Description

Part Number

18 Channel Servo Driver Shield

SCX18.S

HS311 Standard hobby servo

HS311

Raspberry-PI, Arduino, NANO, UNO & MEGA are trademark.

DS-SCX18.S

CONTROL MODULES

INTERFACE 13.04.13 Revision 1.00

Power requirements

The DS-SCX18.S takes the power

necessary for operation (approx. 2-

25mA) from an external battery or

power adaptor or power from the

Arduino or Raspberry-PI board.

The SCX18 provides three PCB

pads, two marked ‘GND’ and one

marked ‘Vin’ in the same format as

that present on the UNO board,

which should be connected to nega-

tive and positive battery/power sup-

ply terminals respectively. The input

voltage range is 4.75 - 16VDC with

the internal circuitry being protected

against power supply reversal.

The two on-board servo regulators

provide a clean regulated 5V supply

for the connected servos at a maxi-

mum current of 3Amps each, the left

hand regulator powering servos 1 to

9 and the right hand regulator servos

10-18. The following table indicates

if a regulator needs to be enabled or

disabled dependant on supply volt-

age:

Status Battery pack/supply voltage

Disabled 3.6V to 4.8V

Enabled 7.2V to 8.5V

The servo regulators are enabled or

disabled with on-board double links

just above the regulator heat-sinks

which can be configured as follows:

Enabled (ON):

Disabled (OFF):

Refer to the voltage rating of the

servos you wish to use before con-

figuring the servo regulator.

Connection of the external supply -

battery / mains adaptor - to the

SCX18 module is through a two (2)

way pluggable screw terminal block

marked ‘3-8.5VDC @ 6A Max’.

Note: This supply is NOT reverse

connection protected but is

marked with a series of ‘+++++’

signs to denote positive.

I2C connection

The I2C connections are marked

‘SDA’ and ‘SCL’ and allow connec-

tion to the Arduino UNO board

‘ANALOG IN’ pins 4 and 5 or the

Rasperberry-PI GPIO port pins 3

and 5 (see Fig. 2.0) or another I2C

Master device.

The DS-SCX18.S is fitted with pull-

up jumpers that can be configured to

provide the source current necessary

for I2C communication. The follow-

ing jumpers should normally be set

when using the UNO board, as long

as the I2C bus does not have existing

pull-up’s provided by another de-

vice. These jumpers MUST be

removed when using the Raspber-

ry-PI:

I2C communication

Up to four DS-SCX18.S modules

may be connected to the same UNO

/ Raspberry-PI board or I2C bus and

accessed individually using their

own individual address.

The address is configured with the

following jumpers:

The following table shows how the

jumpers are placed for the different

binary addresses:

Address xx A0 A1

00 (default) ON ON

01 OFF ON

10 ON OFF

11 OFF OFF

The binary address (xx) above is

used in conjunction with the device

ID 11101xxD to form the complete

device address i.e. if both jumpers

are left connected (default) then the

device address would be

1110100Dbinary.

The ‘D’ bit determines if a read or a

write to the SCX18 is to be per-

formed. If the ‘D’ bit is set ‘1’ then

a register read is performed or if

clear ‘0’ a register write.

To access individual registers a de-

vice write must be undertaken by the

I2C Master which consists of a Start

condition, device ID (‘D’ bit

cleared), register to start write, one

or more bytes of data to be written

and a stop condition (see Figure 1.0

for I2C write protocol).

There are 37 individual registers that

can be written within the SCX18

that control output as follows:

SCX I2C address

1. 1 1 1 0 1 X X 0

XX = SCX18 address

R0 U U B B B B B B

B..B = 0 to 37

U..U = unused on this implementation

Servo 1 position

R1 P P P P P P P P

P..P = Servo position 0 to 255 (0.5mS to 2.50mS)

Servo 1 control

R2 A B C D S S S S

A = Operate (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start control (0 – Disabled 1 – Enabled)

D = Speed control (0 – Disabled 1 – Enabled)

S..S = Servo speed value 0 to 15 (0 = slowest)

Servo 2 position

R3 P P P P P P P P

P..P = Servo position 0 to 255 (0.5mS to 2.50mS)

Servo 2 control

R4 A B C D S S S S

A = Operate (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start control (0 – Disabled 1 – Enabled)

D = Speed control (0 – Disabled 1 – Enabled)

S..S = Servo speed value 0 to 15 (0 = slowest)

Servo 3 position

R5 P P P P P P P P

P..P = Servo position 0 to 255 (0.5mS to 2.50mS)

Servo 3 control

R6 A B C D S S S S

A = Operate (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start control (0 – Disabled 1 – Enabled)

D = Speed control (0 – Disabled 1 – Enabled)

S..S = Servo speed value 0 to 15 (0 = slowest)

Servo 4 position

R7 P P P P P P P P

P..P = Servo position 0 to 255 (0.5mS to 2.50mS)

Servo 4 control

R8 A B C D S S S S

A = Operate (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start control (0 – Disabled 1 – Enabled)

D = Speed control (0 – Disabled 1 – Enabled)

S..S = Servo speed value 0 to 15 (0 = slowest)

Servo 5 position

R9 P P P P P P P P

P..P = Servo position 0 to 255 (0.5mS to 2.50mS)

Servo 5 control

R10 A B C D S S S S

A = Operate (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start control (0 – Disabled 1 – Enabled)

D = Speed control (0 – Disabled 1 – Enabled)

S..S = Servo speed value 0 to 15 (0 = slowest)

Servo 6 position

R11 P P P P P P P P

P..P = Servo position 0 to 255 (0.5mS to 2.50mS)

Servo 6 control

R12 A B C D S S S S

A = Operate (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start control (0 – Disabled 1 – Enabled)

D = Speed control (0 – Disabled 1 – Enabled)

S..S = Servo speed value 0 to 15 (0 = slowest)

SDA

SCL

PULL UP

ADDRESS

INTERFACE 13.04.13 Revision 1.00

Servo 7 position

R13 P P P P P P P P

P..P = Servo position 0 to 255 (0.5mS to 2.50mS)

Servo 7 control

R14 A B C D S S S S

A = Operate (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start control (0 – Disabled 1 – Enabled)

D = Speed control (0 – Disabled 1 – Enabled)

S..S = Servo speed value 0 to 15 (0 = slowest)

Servo 8 position

R15 P P P P P P P P

P..P = Servo position 0 to 255 (0.5mS to 2.50mS)

Servo 8 control

R16 A B C D S S S S

A = Operate (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start control (0 – Disabled 1 – Enabled)

D = Speed control (0 – Disabled 1 – Enabled)

S..S = Servo speed value 0 to 15 (0 = slowest)

Servo 9 position

R17 P P P P P P P P

P..P = Servo position 0 to 255 (0.5mS to 2.50mS)

Servo 9 control

R18 A B C D S S S S

A = Operate (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start control (0 – Disabled 1 – Enabled)

D = Speed control (0 – Disabled 1 – Enabled)

S..S = Servo speed value 0 to 15 (0 = slowest)

Servo 10 position

R19 P P P P P P P P

P..P = Servo position 0 to 255 (0.5mS to 2.50mS)

Servo 10 control

R20 A B C D S S S S

A = Operate (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start control (0 – Disabled 1 – Enabled)

D = Speed control (0 – Disabled 1 – Enabled)

S..S = Servo speed value 0 to 15 (0 = slowest)

Servo 11 position

R21 P P P P P P P P

P..P = Servo position 0 to 255 (0.5mS to 2.50mS)

Servo 11 control

R22 A B C D S S S S

A = Operate (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start control (0 – Disabled 1 – Enabled)

D = Speed control (0 – Disabled 1 – Enabled)

S..S = Servo speed value 0 to 15 (0 = slowest)

Servo 12 position

R23 P P P P P P P P

P..P = Servo position 0 to 255 (0.5mS to 2.50mS)

Servo 12 control

R24 A B C D S S S S

A = Operate (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start control (0 – Disabled 1 – Enabled)

D = Speed control (0 – Disabled 1 – Enabled)

S..S = Servo speed value 0 to 15 (0 = slowest)

Servo 13 position

R25 P P P P P P P P

P..P = Servo position 0 to 255 (0.5mS to 2.50mS)

Servo 13 control

R26 A B C D S S S S

A = Operate (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start control (0 – Disabled 1 – Enabled)

D = Speed control (0 – Disabled 1 – Enabled)

S..S = Servo speed value 0 to 15 (0 = slowest)

Servo 14 position

R27 P P P P P P P P

P..P = Servo position 0 to 255 (0.5mS to 2.50mS)

Servo 14 control

R28 A B C D S S S S

A = Operate (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start control (0 – Disabled 1 – Enabled)

D = Speed control (0 – Disabled 1 – Enabled)

S..S = Servo speed value 0 to 15 (0 = slowest)

Servo 15 position

R29 P P P P P P P P

P..P = Servo position 0 to 255 (0.5mS to 2.50mS)

Servo 15 control

R30 A B C D S S S S

A = Operate (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start control (0 – Disabled 1 – Enabled)

D = Speed control (0 – Disabled 1 – Enabled)

S..S = Servo speed value 0 to 15 (0 = slowest)

Servo 16 position

R31 P P P P P P P P

P..P = Servo position 0 to 255 (0.5mS to 2.50mS)

Servo 16 control

R32 A B C D S S S S

A = Operate (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start control (0 – Disabled 1 – Enabled)

D = Speed control (0 – Disabled 1 – Enabled)

S..S = Servo speed value 0 to 15 (0 = slowest)

Servo 17 position

R33 P P P P P P P P

P..P = Servo position 0 to 255 (0.5mS to 2.50mS)

Servo 17 control

R34 A B C D S S S S

A = Operate (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start control (0 – Disabled 1 – Enabled)

D = Speed control (0 – Disabled 1 – Enabled)

S..S = Servo speed value 0 to 15 (0 = slowest)

Servo 18 position

R35 P P P P P P P P

P..P = Servo position 0 to 255 (0.5mS to 2.50mS)

Servo 18 control

R36 A B C D S S S S

A = Operate (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start control (0 – Disabled 1 – Enabled)

D = Speed control (0 – Disabled 1 – Enabled)

S..S = Servo speed value 0 to 15 (0 = slowest)

Servo global enable register

R37 X X X X X X X X

X..X = Any value

Each control register consists of four

control bits and a four bit speed con-

trol value defined as follows:

Bit (A) 128decimal is the operate bit

which when set activates the servo

being controlled.

Bit (B) 64decimal is the reverse bit

which reverses the position value for

the servo being controlled.

Bit (C) 32decimal is the soft-start bit

which when set on servo first activa-

tion, see operate bit above, feeds

position pulses to the servo in a

ramping manner until position is

attained.

Bit (D) 16decimal is the speed control

enable bit which when set applies

the speed value 0 to 15, contained in

the four bits (SSSS) 1,2,4,8 decimal , to

the servo being controlled.

Once all the required position &

control registers have been set a

write to the R37 (Global enable reg-

ister) must be made to activate all

the new positions.

Example.

To set the first nine servos to new positions

with servos 1 to 4 running at speed 0 and

servos 5 to 8 running at speed 5 in reverse

mode, first write:

Byte 1 (SCX18 Adr) 11101000binary

Byte 2 (Register 0) 0decimal

Byte 3 (Register 1) 30decimal

Byte 4 (Register 2) 144decimal, 90hex

Byte 5 (Register 3) 35decimal

Byte 6 (Register 4) 144decimal, 90hex

Byte 7 (Register 5) 40decimal

Byte 8 (Register 6) 144decimal, 90hex

Byte 9 (Register 7) 45decimal

Byte 10 (Register 8) 144decimal, 90hex

Byte 11 (Register 9) 127decimal

Byte 12 (Register 10) 213decimal, D5hex

Byte 13 (Register 11) 130decimal

Byte 14 (Register 12) 213decimal, D5hex

Byte 15 (Register 13) 140decimal

Byte 16 (Register 14) 213decimal, D5hex

Byte 17 (Register 15) 150decimal

Byte 18 (Register 16) 213decimal, D5hex

then to activate write:

Byte 1 (SCX18 Adr) 11101000binary

Byte 2 (Register 0) 37decimal

Byte 3 (Register 37) 0decimal

To read the status registers a device

write then read must be undertaken

by the OOPic / I2C Master. The

write consists of a Start condition,

device ID (‘D’ bit cleared), register

to start read and a Stop condition.

This is followed by a read, which

consists of a Start condition, device

ID (‘D‘ bit set), followed by data

from the status register and termi-

nated with a Stop condition (see

Figure 1.1 for I2C read protocol).

Status registers

There are 18 registers that can be

read within the SCX18 as follows:

SCX I2C Address

1. 1 1 1 0 1 X X 1

XX = SCX18 address

Servo 1 status

R0 A B C D 0 0 0 0

A = Operation (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start (0 – Complete 1 – In-progress)

D = Movement (0 – Complete 1 – In-progress)

Servo 2 status

R1 A B C D 0 0 0 0

A = Operation (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start (0 – Complete 1 – In-progress)

D = Movement (0 – Complete 1 – In-progress)

Servo 3 status

R2 A B C D 0 0 0 0

A = Operation (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start (0 – Complete 1 – In-progress)

D = Movement (0 – Complete 1 – In-progress)

Servo 4 status

R3 A B C D 0 0 0 0

A = Operation (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start (0 – Complete 1 – In-progress)

D = Movement (0 – Complete 1 – In-progress)

Servo 5 status

R4 A B C D 0 0 0 0

A = Operation (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start (0 – Complete 1 – In-progress)

D = Movement (0 – Complete 1 – In-progress)

Servo 6 status

R5 A B C D 0 0 0 0

A = Operation (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start (0 – Complete 1 – In-progress)

D = Movement (0 – Complete 1 – In-progress)

INTERFACE 13.04.13 Revision 1.00

Servo 7 status

R6 A B C D 0 0 0 0

A = Operation (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start (0 – Complete 1 – In-progress)

D = Movement (0 – Complete 1 – In-progress)

Servo 8 status

R7 A B C D 0 0 0 0

A = Operation (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start (0 – Complete 1 – In-progress)

D = Movement (0 – Complete 1 – In-progress)

Servo 9 status

R8 A B C D 0 0 0 0

A = Operation (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start (0 – Complete 1 – In-progress)

D = Movement (0 – Complete 1 – In-progress)

Servo 10 status

R9 A B C D 0 0 0 0

A = Operation (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start (0 – Complete 1 – In-progress)

D = Movement (0 – Complete 1 – In-progress)

Servo 11 status

R10 A B C D 0 0 0 0

A = Operation (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start (0 – Complete 1 – In-progress)

D = Movement (0 – Complete 1 – In-progress)

Servo 12 status

R11 A B C D 0 0 0 0

A = Operation (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start (0 – Complete 1 – In-progress)

D = Movement (0 – Complete 1 – In-progress)

Servo 13 status

R12 A B C D 0 0 0 0

A = Operation (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start (0 – Complete 1 – In-progress)

D = Movement (0 – Complete 1 – In-progress)

Servo 14 status

R13 A B C D 0 0 0 0

A = Operation (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start (0 – Complete 1 – In-progress)

D = Movement (0 – Complete 1 – In-progress)

Servo 15 status

R14 A B C D 0 0 0 0

A = Operation (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start (0 – Complete 1 – In-progress)

D = Movement (0 – Complete 1 – In-progress)

Servo 16 status

R15 A B C D 0 0 0 0

A = Operation (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start (0 – Complete 1 – In-progress)

D = Movement (0 – Complete 1 – In-progress)

Servo 17 status

R16 A B C D 0 0 0 0

A = Operation (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start (0 – Complete 1 – In-progress)

D = Movement (0 – Complete 1 – In-progress)

Servo 18 status

R17 A B C D 0 0 0 0

A = Operation (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start (0 – Complete 1 – In-progress)

D = Movement (0 – Complete 1 – In-progress)

Firmware version

R18 M M M M V V V V

M..M = Firmware major revision number 1-15

V..V = Firmware minor revision number 1-15

Bit (A) 128decimal is the operate bit

which when set indicates that the

servo is operational.

Bit (B) 64decimal is the reverse bit

which when set indicates that posi-

tion values written to the servo will

be reversed.

Bit (C) 32decimal is the soft-start bit

which when set indicates that soft-

start is in progress.

Movement complete determination

Bit (D) 16decimal is cleared to indicate

if the current servo movement has

completed.

This indication is not derived from

mechanical or electrical feedback

from the servo being controlled but

is a function of the current servo

speed selected and position.

When the slowest servo speed (0) is

selected the determination of

movement completion is at its best.

This is because the positional

change of the servo between its cur-

rent and final position has been split

into many sub-positions which must

be attained before the final position

is reached. These many sub-

positions ensure that the mechanical

position closely relates to the posi-

tion requested by the pulse width

and therefore the determination of

final position (movement complete)

will closely relate to mechanical

position. As servo speed is increased

the error between mechanical posi-

tion and pulse width position in-

creases and movement completion

accuracy is degraded.

Electrical Characteristics (TA = 25oC Typical)

Parameter

Minimum

Max

mum

Units

Notes

Supply Voltage (Servo power)

3.8

Supply Current (Servo power)

2x 2800

Supply Voltage (on

board VCC)

4.75

Supply Current (on

board VCC)

I2C pull

up resistance

4700



C speed

400

kHz

Absolute Maximum Ratings

Parameter

Minimum

Max

mum

Units

Notes

Supply Voltage (Servo power

)

0.5

+30

Supply Current (Servo power

)

4.5

Environmental

Parameter

Minimum

Max

mum

Units

Operating Temperature

Storage Temperature

Humidity

Dimensions

Length

56.25mm, Width 53.5mm, Height 15

Weight

Immunity & emissions

See statement on page 8

Notes:

1.Servo voltage below 5V requires that the servo regulator be disabled (see above).

2.Voltages above 6-12V may require force cooling of the heat-sinks if servo load is high.

3.Values given are based on maximum and minimum loading for each regulator.

4.Values given are for servos being not driven and driven.

5.Value given is based on maximum and minimum loading.

INTERFACE 13.04.13 Revision 1.00

Calculating binary bit values:

The registers used above use the binary notation to allow the control of servo operation, reversal, soft-start & speed selection. Each regis-

ter is made up of eight (8) bits, which can be set or cleared to produce the desired operation, the individual bits having a value associated

with them as follows:

128 64 32 16 8 4 2 1

If we take for example one of the servo control registers we can see it is made up of four (4) separate bits A, B, C & D plus a four bit

value SSSS:

Servo 1 control

R1 A B C D S S S S

A = Operate (0 – Servo disabled 1 – Servo enabled)

B = Reverse (0 – Servo normal 1 – Servo reversed)

C = Soft-start control (0 – Disabled 1 – Enabled)

D = Speed control (0 – Disabled 1 – Enabled)

S..S = Servo speed value 0 to 15 (0 = slowest)

Each bit is defined to control a particular function for the servo it controls, so if for example we wanted to enable servo 1 we would need

to set bit ‘A’ which controls the servo operation. We know from the bit values defined above that the value associated with the ‘A’ bit is

128, so by writing this value to register 1 we can enable servo 1. If we need to enable additional functions such as the speed control - ‘D’

- as well as the servo enable, the value of this bit is added to the value written to the register i.e. 128 + 16 = 144. In addition we could

also add a speed value of 5 that would make the total value 128 + 16 + 5 = 149.

Figure 1.0 (I2C write protocol)

START

ACK

SCX18 ADDRESS REGISTER

ADDRESS

01 1 1A1 A0

R / W=0

ACK

DATA

BYTE

STOP

Multiple bytes may be written before the ‘STOP’ condition. Data is written into registers starting at ‘REGISTER ADDRESS’, then ‘REGISTER AD-

DRESS’ +1, then ‘REGISTER ADDRESS’ +2 etc.

Each byte transfer is acknowledged ‘ACK’ by the SCX18 until the ‘STOP’ condition.

Figure 1.1 (I2C read protocol)

START

ACK

SCX18 ADDRESS REGISTER

ADDRESS

ACK

DATA

BYTE 1

STOP

START

ACK

GPM ADDRESS

NACK

DATA

BYTE 2

01 1 1 A1 A01

R / W=0

01 1 1A1 A0

R / W=1

‘DATA BYTE 1 & 2’ are register values returned from the SCX18. Each byte written is acknowledged ‘ACK’ by the SCX18 , every byte read is

acknowledged ‘ACK’ by the I2C Master. A Not-acknowledge ‘NACK’ condition is generated by the I2C Master when it has finished reading.

INTERFACE 13.04.13 Revision 1.00

Figure 2.0 (Connection Schematic for Arduino UNO or Raspberry-Pi I2C communication)

SDA

SCL

PULL-UP

ADDRESS

SDA SCL

www.arduino.cc

RESET

3V3

5V Gnd Vin 0 1 2 3 4 5

ANALOG INPOWER

Raspberry Pi

with speed control

18 Channel Servo Driver

DS-SCX18.Shield

SV V+GND

++++

@6A Max

OFFON

DV070_V1.00.01

3 - 8.5VDC

CN1

D1 C2

R5 C7 C6

R2 C4 C3

OFFON

++++

5V@3A Max

BLACK

RED

YELLOW

GREEN

INTERFACE 13.04.13 Revision 1.00

53.50

56.25

15.00

SDA

SCL

PULL-UP

ADDRESS

with speed control

18 Channel Servo Driver

DS-SCX18.Shield

SV V+GND

++++

@6A Max

OFFON

DV070_V1.00.01

3 - 8.5VDC

CN1

D1 C2

R5 C7 C6

R2 C4 C3

OFFON

++++

5V@3A Max

Revision History:

1.00 Release version

Mechanical Specifications – Units millimetres

INTERFACE 13.04.13 Revision 1.00

WEEE Consumer Notice

This product is subject to Directive 2002/96/EC of the European Parliament and the Council of the Euro-

pean Union on Waste of Electrical and Electronic Equipment (WEEE) and, in jurisdictions adopting that

Directive, is marked as being put on the market after August 13, 2005, and should not be disposed of as

unsorted municipal/public waste. Please utilise your local WEEE collection facilities in the disposition and

otherwise observe all applicable requirements. For further information on the requirements regarding the disposition of

this product in other languages please visit www.designersystems.co.uk

RoHS Compliance

This product complies with Directive 2002/95/EC of the European Parliament and the Council of the Eu-

ropean Union on the Restriction of Hazardous Substances (RoHS) which prohibits the use of various

heavy metals (lead, mercury, cadmium, and hexavalent chromium), polybrominated biphenyls (PBB) and

polybrominated diphenyl ethers (PBDE).

Apparatus name / model number DS-SCX18.S Manufacturer Designer Systems, 11 Castle Street, Truro, Cornwall

Conformity via Generic Standard EN61000-1 TR1 3AF, United Kingdom

Generic Standard EN61000-3 Description of apparatus Robotic interface peripheral

Conformity criteria For use only within commercial, residential and light industrial applications

We certify that the apparatus identified above conforms to the requirements of Council Directive 2004/108/EC & 2006/95/EC

Signed. Date 20/6/13

Having made this declaration the CE mark is affixed to this product, its packaging, manual or warranty.

The information appearing in this data sheet is believed to be accurate at the time of publication. However, Designer Systems assumes no responsibility arising from the use of the infor-

mation supplied. The applications mentioned herein are used solely for the purpose of illustration and Designer Systems makes no warranty or representation that such applications will be

suitable without further modification, nor recommends the use of its products for application that may present a risk to human life due to malfunction or otherwise. Designer Systems reserves

the right to alter its products without prior notification.