The Starlight Xpress Universal Filter Wheel

Handbook for the SX Universal Filter Wheel - Issue 1, May 2009Handbook for the Starlight Xpress Universal Filter WheelThank you for your purchase of a Starlight Xpress Universal Filter Wheel. We hopethat 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 lesssophisticated designs:1) The wheel uses an internal sub-miniature DC motor drive to turn the filterplate. This consumes far less power than the more typical stepper motor andallows wheel operation directly from the USB input, thus eliminating thecumbersome power supply and extra power cable. The DC drive also producesa quiet and vibration-free filter translation and eliminates a significant amountof bulk and weight.2) The filter locations are encoded by 3 Hall-effect magnetic sensors, whichpermit up to 7 unique filter positions to be defined. The control software canspecify a particular filter without prior knowledge of the location of ‘position1’ – 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 2009optical sensors also prevents stray infrared light from entering the CCDcamera and causing strange image artefacts.3) Although USB operation is the normal mode, the extra RJ12 socket alsopermits serial port control or ‘handbox’ manual control. The Universal FilterWheel truly is ‘Universal’!4) The input and output adaptors are both removable and also may be oriented atany rotational angle to set the wheel and camera into optimum positions. Thestandard ‘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 32.5mmfilter positions and the other with five x 48mm filter locations. These areeasily swapped by removing 6 ‘thumbscrew’ fixings and simply dropping theplate into place. There are no gears or belt drives to engage and the plate dropsdirectly into contact with the motor drive drum. Easily done, even byflashlight!6) The ultra-slim design of the SXUFW minimises the loss of optical back focaldistance to only 29mm overall (including the T thread adaptors).Here is a simplified cross-sectional view of the filter wheelLoading the filters:Open the wheel by unscrewing the 5 small thumbscrews from around the periphery ofthe wheel chamber and the single large thumbscrew from the central pillar. Carefullylift off the side wall and put it in a safe place. You will now see the filter plate andyou can lift it off the centre bearing and place it down with the magnet screws facingupwards. 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 2009Installing the software:No drivers are required for the SXUFW. The USB input is an ‘HID’ device whichWindows recognises automatically, and the serial input does not use a special driver.Popular third-party software, such as AstroArt and MaximDL include the commandsets for the SXUFW, and the latest SX software can be used with the wheel. You mayalso 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 computerand will display a filter wheel control panel when executed. It may be found useful forboth testing the wheel and operating it when the camera software does not support theSX wheel protocols.Connecting up the wheel:USB control:If you are using USB control, then the only connection required is that between theUSB port on the wheel and a USB output on your computer. You may, of course, usea USB hub, if necessary – a powered hub is recommended to ensure that the wheelmotor has sufficient torque to operate reliably. When the wheel is first connected,Windows will display a message about ‘New hardware found’ followed by ‘SX filterwheel’. Shortly afterwards, the wheel will rotate twice as it calibrates and determinesthe 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 serialport. 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 wheelmotor and so the cable is modified to allow the connection of a small 9v battery at thePC end. Just clip a 9v radio battery (PP3 or R22) to the snap connectors and thenconnect the serial socket to the PC serial port. No power will be taken until the RJ12plug is inserted into the wheel socket. Disconnect the cable when not in use, or thebattery will be drained in a few hours.Serial control does not require any special drivers. Just determine the correct COMport number and operate the wheel using the control interface provided by thesoftware in use.- 3 -

Handbook for the SX Universal Filter Wheel - Issue 1, May 2009Manual Control:A manual control box is available from Starlight Xpress dealers. The kit includes anRJ12 cable to connect to the serial port of the wheel with the other end plugged intothe manual control box. The box contains a ‘AAA’ size battery clip for 4 cells and a10 position thumb-operated rotary switch (switch positions higher than the maximumnumber of filters will default to the highest number available – i.e. switch positions 8and 9 give filter 7 on a 7 aperture filter wheel). To install the batteries, unscrew thefour cross-head screws in the rear panel of the hand controller and lift it off. Thebattery 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 batterypack will be discharged.Starlight Xpress Universal Filter WheelCommunication ProtocolsInterfaces 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 currently5 or 7.Filter number: This is any number from 1 to (If a Filter Number higher than Total Filters is requested then the FilterNumber is set to )USB Protocol:The SX filter wheel uses a simple “Human Interface Device” protocol, so nospecial driver needs to be installed. The driver is an integral part of theWindows 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 sendan input report in response.The output report data is formatted thus:Description 1 st byte 2 nd byteSelect Filter New Filter number Zero (0)Request current filter number Zero ZeroGet Filter Total Zero One (1)The input report data is formatted thus:Response To: 1 st byte 2 nd byteSelect New FilterNew Filter number Total filtersorZero = filters movingRequest current filter number Current Filter number Total filters- 4 -

Handbook for the SX Universal Filter Wheel - Issue 1, May 2009Get Filter TotalorZero = filters movingCurrent Filter numberorZero = filters movingZeroNB: The ‘Get Filter Total’ command responds straight away with a “filtersmoving” message. However there is a delay of several seconds before theTotal Filters data is available to the “Request Current Filter Number”command. This is the time taken for the wheel to complete between one andtwo complete rotations. During this period the Total Filters will be reported aszero. 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 threecommands thus:Notes: Checksum is 8 bit addition of Header + Command + Data0xA5 is the hexadecimal number = decimal number 1650x20 is the hexadecimal number = decimal number 32Output Command / Data from PCDescription Header(1)Command(2)Data(3)Checksum(4)Select Filter 0xA5 1 0x20 4 = 1+2+3Request Current 0xA5 2 0x20 4 = 1+2+3FilterGet Filter Total 0xA5 3 0x20 4 = 1+2+3Input Data to PCDescription Header(1)Response(2)Data(3)Select Filter 0xA5 0x81 New FilterNumberRequest Current 0xA5 0x82 Filter NumberFilter+ 0x30Get Filter Total 0xA5 0x83 Total Filters +0x30Checksum(4)4 = 1+2+34 = 1+2+34 = 1+2+3Examples, (all characters expressed in hexadecimal):Select Filter Number 3:PC -> Filter Wheel, 0xA5, 0x01, 0x03, 0xA9Filter Wheel -> PC, 0xA5, 0x81, 0x03, 0x29Request Current Filter (which is 2):PC -> Filter Wheel, 0xA5, 0x02, 0x20, 0xC7Filter Wheel -> PC, 0xA5, 0x82, 0x32, 0x59- 5 -

Handbook for the SX Universal Filter Wheel - Issue 1, May 2009Get Filter Total (which is 7):PC -> Filter Wheel, 0xA5, 0x03, 0x20, 0xC8Filter Wheel -> PC, 0xA5, 0x83, 0x37, 0x2F (after delay)Note: The ‘Get Filter Total’ command has a delay of several seconds beforethe response is sent back. This is the time taken for the wheel to completebetween one and two rotations. When completed, filter 1 is selected. Do notsend any new requests until the response is received. Any data sent during thisperiod would be read but then discarded.- 6 -

The Starlight Xpress Universal Filter Wheel

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