Designer Systems DS-SCX18.S Manual Download Page 2

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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.

C connection

The I

C 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 I

Master device.

The DS-SCX18.S is fitted with pull-
up jumpers that can be configured to
provide the source current necessary
for I

C communication. The follow-

ing jumpers should normally be set
when using the UNO board, as long
as the I

C bus does not have existing

pull-up’s provided by another de-
vice.

These jumpers MUST be

removed when using the Raspber-
ry-PI:

C communication

Up to four DS-SCX18.S modules
may be connected to the same UNO
/ Raspberry-PI board or I

C 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

00 (default)

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
1110100D

binary

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
I

C 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 I

C write protocol).

There are 37 individual registers that
can be written within the SCX18
that control output as follows:

SCX I2C address

XX = SCX18 address

Register address
R0

B..B = 0 to 37
U..U = unused on this implementation

Servo 1 position
R1

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

Servo 1 control
R2

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