Starlight Xpress SX User Manual

Handbook for the SX Universal Filter Wheel - Issue 1, May 2009

Handbook for the Starlight Xpress Universal Filter Wheel

Thank you for your purchase of a Starlight Xpress Universal Filter Wheel. We hope
that you will enjoy using this advanced SX unit, which offers many unique features.
This handbook will help you to put it into operation and to understand its capabilities.
Please read it carefully.

Description:

The SX Universal Filter Wheel has several important advantages over older and less
sophisticated designs:

1) The wheel uses an internal sub-miniature DC motor drive to turn the filter

plate. This consumes far less power than the more typical stepper motor and
allows wheel operation directly from the USB input, thus eliminating the
cumbersome power supply and extra power cable. The DC drive also produces
a quiet and vibration-free filter translation and eliminates a significant amount
of bulk and weight.

2) The filter locations are encoded by 3 Hall-effect magnetic sensors, which

permit up to 7 unique filter positions to be defined. The control software can
specify a particular filter without prior knowledge of the location of ‘position
1’ – so the filters can never get out of sequence. The lack of any infrared

- 1 -

Handbook for the SX Universal Filter Wheel - Issue 1, May 2009

optical sensors also prevents stray infrared light from entering the CCD
camera and causing strange image artefacts.

3) Although USB operation is the normal mode, the extra RJ12 socket also

permits serial port control or ‘handbox’ manual control. The Universal Filter
Wheel truly is ‘Universal’!

4) The input and output adaptors are both removable and also may be oriented at

any rotational angle to set the wheel and camera into optimum positions. The
standard ‘T’ thread adaptors may be replaced with other versions for ‘SCT’
thread etc. simply by unscrewing three fixing bolts.

5) Two interchangeable filter plates are available – one with seven x 32.5mm

filter positions and the other with five x 48mm filter locations. These are
easily swapped by removing 6 ‘thumbscrew’ fixings and simply dropping the
plate into place. There are no gears or belt drives to engage and the plate drops
directly into contact with the motor drive drum. Easily done, even by
flashlight!

6) The ultra-slim design of the SXUFW minimises the loss of optical back focal

distance to only 29mm overall (including the T thread adaptors).

Here is a simplified cross-sectional view of the filter wheel

Loading the filters:

Open the wheel by unscrewing the 5 small thumbscrews from around the periphery of
the wheel chamber and the single large thumbscrew from the central pillar. Carefully
lift off the side wall and put it in a safe place. You will now see the filter plate and
you can lift it off the centre bearing and place it down with the magnet screws facing
upwards. Your filters may now be screwed into the plate from the magnet screw side,
placing them in the desired numerical order according to the engraving on the plate.
Assemble the wheel by reversing the sequence of operations above.

- 2 -

Handbook for the SX Universal Filter Wheel - Issue 1, May 2009

Installing the software:

No drivers are required for the SXUFW. The USB input is an ‘HID’ device which
Windows recognises automatically, and the serial input does not use a special driver.
Popular third-party software, such as AstroArt and MaximDL include the command
sets for the SXUFW, and the latest SX software can be used with the wheel. You may
also use a simple Windows ‘Console’ program, which is provided on the CD ROM.
This program, ‘SX Filter Wheel.exe’, may be copied into a folder on your computer
and will display a filter wheel control panel when executed. It may be found useful for
both testing the wheel and operating it when the camera software does not support the
SX wheel protocols.

Connecting up the wheel:

USB control:

If you are using USB control, then the only connection required is that between the
USB port on the wheel and a USB output on your computer. You may, of course, use
a USB hub, if necessary – a powered hub is recommended to ensure that the wheel
motor has sufficient torque to operate reliably. When the wheel is first connected,
Windows will display a message about ‘New hardware found’ followed by ‘SX filter
wheel’. Shortly afterwards, the wheel will rotate twice as it calibrates and determines
the number of filter positions available. It is now in position 1 and ready to use.

Serial control:

The SXUFW requires a special RJ12 cable that must be used to connect via the serial
port. This is available from Starlight Xpress dealers, if you wish to use serial control.
The serial port of a PC cannot supply sufficient power to operate the filter wheel
motor and so the cable is modified to allow the connection of a small 9v battery at the
PC end. Just clip a 9v radio battery (PP3 or R22) to the snap connectors and then
connect the serial socket to the PC serial port. No power will be taken until the RJ12
plug is inserted into the wheel socket. Disconnect the cable when not in use, or the
battery will be drained in a few hours.

Serial control does not require any special drivers. Just determine the correct COM
port number and operate the wheel using the control interface provided by the
software in use.

- 3 -

Handbook for the SX Universal Filter Wheel - Issue 1, May 2009

Manual Control:

A manual control box is available from Starlight Xpress dealers. The kit includes an
RJ12 cable to connect to the serial port of the wheel with the other end plugged into
the manual control box. The box contains a ‘AAA’ size battery clip for 4 cells and a
10 position thumb-operated rotary switch (switch positions higher than the maximum
number of filters will default to the highest number available – i.e. switch positions 8
and 9 give filter 7 on a 7 aperture filter wheel). To install the batteries, unscrew the
four cross-head screws in the rear panel of the hand controller and lift it off. The
battery holder may then be lifted out and fitted with four AAA cells.
Please be sure to disconnect the hand controller when it is not in use, or the battery
pack will be discharged.

Starlight Xpress Universal Filter Wheel

Communication Protocols

Interfaces available:

(a) USB: 1.1 or 2.0
(b) Serial Port: 9600 baud, 8 data bits, no parity, 1 stop bit.
(c) Manual Switch: Select filter using digital switch box.

General parameters:

Total Filters: This is the number of filters fitted on the wheel, and is currently

5 or 7.

Filter number: This is any number from 1 to <Total Filters>

(If a Filter Number higher than Total Filters is requested then the Filter
Number is set to <Total Filters>)

USB Protocol:

The SX filter wheel uses a simple “Human Interface Device” protocol, so no
special driver needs to be installed. The driver is an integral part of the
Windows PC operating system.
Communications between the PC & filter wheel is by input and output reports
(referenced to the PC). These reports are both of a fixed length of two bytes.
The PC sends the output report and the filter wheel, about 1ms later, will send
an input report in response.

The output report data is formatted thus:

Description 1st byte 2nd byte

Select Filter New Filter number Zero (0)
Request current filter number Zero Zero
Get Filter Total Zero One (1)

The input report data is formatted thus:

Response To: 1st byte 2nd byte

Select New Filter New Filter number

or
Zero = filters moving

Request current filter number Current Filter number Total filters

Total filters

- 4 -

Handbook for the SX Universal Filter Wheel - Issue 1, May 2009

Get Filter Total Current Filter number

NB: The ‘Get Filter Total’ command responds straight away with a “filters
moving” message. However there is a delay of several seconds before the
Total Filters data is available to the “Request Current Filter Number”
command. This is the time taken for the wheel to complete between one and
two complete rotations. During this period the Total Filters will be reported as
zero. When this command is completed filter 1 is automatically selected.

Serial Port Protocol:

The SX filter wheel implements a four-character format, which has just three
commands thus:

Notes: Checksum is 8 bit addition of Header + Command + Data
0xA5 is the hexadecimal number = decimal number 165

0x20 is the hexadecimal number = decimal number 32

Output Command / Data from PC

Description Header

Select Filter 0xA5 1 0x20 4 = 1+2+3
Request Current
Filter
Get Filter Total 0xA5 3 0x20 4 = 1+2+3

Input Data to PC

Description Header

Select Filter 0xA5 0x81 New Filter

Request Current
Filter
Get Filter Total 0xA5 0x83 Total Filters +

Examples, (all characters expressed in hexadecimal):

Select Filter Number 3:
PC -> Filter Wheel, 0xA5, 0x01, 0x03, 0xA9
Filter Wheel -> PC, 0xA5, 0x81, 0x03, 0x29

Request Current Filter (which is 2):
PC -> Filter Wheel, 0xA5, 0x02, 0x20, 0xC7
Filter Wheel -> PC, 0xA5, 0x82, 0x32, 0x59

or
Zero = filters moving

Zero
or
Zero = filters moving

(1)

Command

(2)

Data

(3)

Checksum

(4)

0xA5 2 0x20 4 = 1+2+3

(1)

Response

(2)

Data

(3)

Checksum

(4)

4 = 1+2+3

Number

0xA5 0x82 Filter Number

4 = 1+2+3

+ 0x30

4 = 1+2+3

0x30

- 5 -

Handbook for the SX Universal Filter Wheel - Issue 1, May 2009

Get Filter Total (which is 7):
PC -> Filter Wheel, 0xA5, 0x03, 0x20, 0xC8
Filter Wheel -> PC, 0xA5, 0x83, 0x37, 0x2F (after delay)

Note: The ‘Get Filter Total’ command has a delay of several seconds before
the response is sent back. This is the time taken for the wheel to complete
between one and two rotations. When completed, filter 1 is selected. Do not
send any new requests until the response is received. Any data sent during this
period would be read but then discarded.

- 6 -