Sky Quality Meter – Lens USB SQM
Contents
1. Revision 1 2 Page 24 Last modified Jul 9 2011 Unihedron SQM LU Users manual 10 Glossary EEPROM Electrically Erasable Programmable Read Only Memory is a type of memory that retains its contents after the power has been removed This type of memory has a limited write erase cycle as well as a lifetime for data retention In the SQM LU the parameters in the micro controller can be written 1 million times and last for 100 years SQM LU Sky Quality Meter with lens and USB connectivity USB Universal Serial Bus Revision 1 2 Page 25 Last modified Jul 9 2011 Unihedron SQM LU Users manual 11 Appendix A revision history 11 1 Manual revision history 1 0 Initial product release 1 1 Troubleshooting and specification addition 1 2 Troubleshooting windows driver addition 11 2 Protocol revision history 3 Initial SQM LE product release 4 Interval report reading includes serial number at end SQM LE 11 3 Feature revision history 9 Initial SQM LE product release 10 Power up default reset for command busy SQM LE 11 Ability to manually sett calibration values SQM LE 12 Temperature averaging added SQM LE 13 Interval report feature added SQM LE 14 Interval report includes serial number Revision 1 2 Page 26 Last modified Jul 9 20112. Table 6 Disarm calibration response An example is zxdL 012345 Revision 1 2 Page 11 Last modified Jul 9 2011 Unihedron SQM LU Users manual 4 2 6 Unit information Unit information command ix provides details about the software in the microcontroller The format of the response is 0 i Indicates that the unit information response is being returned 2 9 00000002 Protocol number 8 digits This will always be the first 8 characters after the i response This value indicates the revision number of the data protocol to from the SQM LU The protocol version is independent of the feature version 11 18 00000003 Model number 8 digits The model value identifies the specific hardware model that the firmware is tailored for 20 27 00000001 Feature number 8 digits The feature value identifies software features independent of the data protocol 29 36 00000413 Serial number 8 digits Each unit has its own unique serial number 37 38 Carriage return Ox0d Line feed 0x0a Table 7 Unit information request response An example is i 00000002 00000003 00000001 00000413 Revision 1 2 Page 12 Last modified Jul 9 2011 Unihedron SQM LU Users manual 4 2 7 Manually set light calibration offset Calibration is done at the factory however in the case where calibration values must be restored or set to something else this command allows
3. Executing the command P X note upper case P sets the period of the timed interval reports to the EEPROM and RAM for booting and immediate use Executing the command p xX note lower case p sets the period of the timed interval reports to RAM only for immediate use The units are seconds For example p0000000360x sets the reporting time to once every 360 seconds 4 2 11 2 Threshold setting for interval reporting Executing the command T ZE note upper case T sets the threshold of the timed interval reports to EEPROM and RAM for boot and immediate use Executing the command t i ZE note lower case t sets the threshold of the timed interval reports to RAM for immediate use only magnitudes arcsecond magnitudes arcsecond The units are For example t00000016 00x limits reporting to values only over 16 00 Revision 1 2 Page 18 Last modified Jul 9 2011 Unihedron SQM LU Users manual 4 2 11 3 Interval setting response Either making the request Ix note upper case I or any request to set the interval report setting produces the following response 0 I Interval settings from EEPROM and RAM are being returned 2 12 0000000360s Interval period that was set into EEPROM 14 24 0000300360s Interval period that was set into RAM 26 37 00000017 60m Threshold value that was set into EEPROM
4. A to USB B cable supplied USB FTDI VCP driver serial port emulator at 115200baud Physical Size 3 6 x 2 6 x 1 1 Meter precision Each SQM L is factory calibrated The absolute precision of each meter is believed tobe 10 0 10 mag arcsec The difference in zeropoint between each calibrated SQM L is typically 10 0 10 mag sq arcsec Power requirement 18mA from the 5V USB connection Operating temperature range 40 C to 85 C Temperature Accuracy 2 C maximum at 25 C Temperature update rate 4 3 seconds 256 samples taken at 60Hz then averaged Ee i D Siw Unihedron SQM LU Unihedron Illustration 2 Front and back of unit Revision 1 2 Page 4 Last modified Jul 9 2011 Unihedron SQM LU Users manual 3 Hardware connections The SQM LU requires one connection to a USB hub or a PC The maximum length cable per the USB specification is 15ft 3 meters 2 Software development The SQM LU communicates as a standard serial port device using the FTDI software drivers which are available for all major operating system platforms http ftdichip com The SQM LU uses the FTDI FT232R chip Once the driver is installed commands can be sent to the SQM LU using a serial terminal emulator to the serial communications port that the device routes to When connecting the SQM LU to a PC where the FTDI device driver is loaded the serial port label will
5. Cause Driver is not installed or the SQM LU is not connected Solution For Windows Check in the control panel for the device and allow Windows to install the driver or install the VCP driver provided on the CD You can also check that the unit is registered using the registry editor from the Start menu select Run then type in regedit and press OK For Windows XP and Windows 2000 look here for your device HKEY_LOCAL_MACHINE SYSTEM Enum FTDIBUS VID_0403 PID_6001 Serial_Number 0000 PortName For Windows 98 and Windows ME look here for your device HKEY_LOCAL_MACHINE SYSTEM Enum FTDIBUS VID_0403 PID_6001 Serial_Number 0000 PortName The Serial_Number is printed on the bottom of the unit The above will identify which COM port the SQM LU has been assigned If the SQM LU is plugged in the active COM port will show up in this list HK_LOCAL_MACHINE HARDWARE DEVICEMAP SERIALCOMM For Linux and Mac use 1lshal to determine which device the FTDI driver has attached the SQM LU to The CD contains a Perl script findftdi p1 to filter out the Ishal output Revision 1 2 Page 23 Last modified Jul 9 2011 Unihedron SQM LU Users manual 9 Company contact information Mailing address Unihedron 4 Lawrence Avenue Grimsby Ontario L3M 2L9 Canada Telephone 905 945 1197 Fax 905 945 6770 Website unihedron com Email info unihedron com
6. a new calibration value to be placed into the SQM LU Executing the command zcal5 x manually sets the light calibration offset to the ake wei he theming CO arcsecond The format of the response is 0 Z Calibration response is being returned 5 Manual Set Light Calibration Offset 4 15 00000017 60m Value that was set into EEPROM 16 17 Carriage return 0x0d Line feed 0x0a Table 8 Response for manual setting of light calibration offset An example is Z 5 00000017 60m Revision 1 2 Page 13 Last modified Jul 9 2011 Unihedron SQM LU Users manual 4 2 8 Manually set light calibration temperature Calibration is done at the factory however in the case where calibration values must be restored or set to something else this command allows a new calibration value to be placed into the SQM LU Executing the command zcalo t x manually sets the light calibration temperature to the value specified in The units are C Note The SQM LU records the temperature in a raw value with different resolution so the reply back may not be exactly the same as the value sent The format of the response is 0 Z Calibration response is being returned 6 Manual Set Light Calibration Offset 4 9 019 0C Value that was set into EEPROM 10 11 Carriage return 0x0d Line feed 0x0a Table 9 Response for manually setting of li
7. be determined at connection time Each SQM LU has a unique serial number usually with a prefix of FT This serial number can be used to identify the exact SQM LU device from other USB devices Interface Program overview Data commands are sent to the SQM LU and it responds with a string of characters A connection must be made to the serial port assigned to the SQM LU Revision 1 2 Page 5 Last modified Jul 9 2011 Unihedron SQM LU Users manual 4 Commands and responses The SQM LU accepts a sequence of characters as a command then executes those commands and usually provides a response of a sequence of characters 4 1 Commands Commands consist of a string of characters The first character is the command type rx Reading request CX Calibration information request ix Unit information request note lower case 1 zcalAx Arm Light Calibration command zcalBx Arm Dark Calibration command zcalDx Disarm Calibration command ZCalS H H4 X Manually Set Light Calibration Offset ZCalOo H H4 xX Manually Set Light Calibration Temperature ZCal7 xX Manually Set Dark Calibration Time Period ZCal8 xX Manually Set Dark Calibration Temperature 0x19 Reset microcontroller see bootloader Hexadecimal value 19 Intel Hex firmware upgrade initiation see bootloader PHHHHHHHHEX Set period in seconds for interval reporting to EEPROM and RAM for
8. 0a Table 3 Calibration information request response An example is C 00000017 60m 0000000 000s 039 4C 00000008 71m 039 4C 0123456789 123456789 123456789 123456789 123456789 1234567 Revision 1 2 Page 8 Last modified Jul 9 2011 Unihedron SQM LU Users manual 4 2 3 Light calibration command Calibration of the SQM LU is done at the factory in a controlled light and temperature environment Executing the Light calibration command zcalAx arms the light calibration mode Flipping the switch to unlock triggers the light calibration and modifies the calibration values in the unit A calibrated light source of approximately 13 5fc is supplied to the sensor The format of the response is 0 Z Indicates that a Calibration response is being returned 1 A Light Calibration 2 a armed 3 L L Locked Wait for unlock before calibrating after Arm command firmware upgrades are disabled U Unlocked Calibrate immediately after Arm command Enable firmware upgrade 4 5 Carriage return 0x0d Line feed 0x0a Table 4 Light calibration response An example is zAaL 012345 Revision 1 2 Page 9 Last modified Jul 9 2011 Unihedron SQM LU Users manual 4 2 4 Dark calibration command Dark Calibration is done at the factory along with Light calibration and calibration temperature recording Executing the dark calibration command zc
9. 39 4C Temperature measured at light sensor in degrees C Leading space for positive value Leading negative sign for negative value 55 63 00000413 Serial number 8 digits Each unit has its own unique serial number 64 65 Carriage return 0x0d Line feed 0x0a Table 12 Interval report An example is r 06 70m 0000022921Hz 0000000020c 0000000 000s 039 4C 00000413 0123456789 123456789 123456789 123456789 123456789 123456789 12345 Revision 1 2 Page 17 Last modified Jul 9 2011 Unihedron SQM LU Users manual Interval reporting is available for sending timed reports to a listening program To prevent reports being sent during daylight when the meter is saturated with light a threshold value can be set Readings exceeding the threshold dark will be reported low readings too bright will be suppressed Due to the construction nature of EEPROM there is a limited number of times that this memory can be written to before it becomes unreliable In the case of the SQM LU the erase write cycle is 1 million times For this reason it is recommended that frequent parameter changes be done in RAM rather than in EPROM Only set the parameter to EEPROM when you want the unit to boot up with your setting See following sections for how to set EEPROM or RAM Loading firmware clears resets the micro controller effectively copying the EEPROM values into RAM 4 2 11 1 Interval reporting period setting
10. 39 50 00000017 60m Threshold value that was set into RAM 51 52 Carriage return 0x0d Line feed 0x0a Table 13 Response of viewing or setting interval reporting parameters An example response is I 0000000360s 0000000360s 00000017 60m 00000017 60m Revision 1 2 Page 19 Last modified Jul 9 2011 Unihedron SQM LU Users manual 5 Electrical connection The SQM LU uses a voltage regulator to bring the incoming USB 5VDC voltage down to 3 3VDC 6 Mechanical installation Unihedron sells an enclosure that is suitable for mounting either the SQM LE or SQM LU into You can read more about it including plans to build your own here http unihedron com projects sqmhousing Illustration 3 Housing 6 1 Cover selection If the unit is to be mounted in exposed location we recommend an acrylic dome Acrylic domes will last 2 3 years but eventually weather on the surface It is not clear that this will affect the reading much The best test would be to swap a weathered and new one back and forth when changing one out Presumably the main consideration would be to keep the domes clean every so often and to make sure that the mounting plane is painted black to that it doesn t reflect light back to the inside of the dome and then back into the meter Source of Acrylic domes http www globalplastics ca domes htm 6 2 Cover calibration Since the SQM LU is not weather proof it must be protected in some
11. Sky Quality Meter Lens USB SQM LU User manual Unihedron SQM LU Users manual Table of Contents l Theory of Opie EE 3 dA OOE E EE 3 DSCC ELC ANIONS cst eras aac ade se cares occa eeu cde cette EE sal teen gue aie E wedded A een eS 4 ER ek 5 nee E ET 5 A Commands and rESPONSES eege A elen dere E a AiE 6 EK eeneg 6 SE 7 er EE 7 4D 2 Ca libration information EIERE eegen E E E Eug 8 42 ds APNE calibration COMMA WEE 9 42 4 Darke calibration command eeni E R E A a E E 10 4 2 5 Disarm calibration command DEE 11 A DO Unit informatio E 12 4 2 7 Manually set light calibration offer 13 4 2 8 Manually set light calibration Temperature 14 4 2 9 Manually set dark calibration time period 15 4 2 10 Manually set dark calibration temperatur 16 4 2 11 Setting interval reporting Parameters sic 4 0c scecceiacedsacscecaseeeacescesepcedhaaacesaeesenaessagecesdendenancsans 17 4 2 11 1 Interval reporting period ETS 18 4 2 11 2 Threshold setting for interval reportng 18 42 11 3 interval setting E 19 SA HAKO eebe E 20 EE E Tee EE 20 6l WT EE 20 GD E EEN 20 6 3 EEN 21 T Default EE 22 Ree e ee 23 EREECHEN 24 WO GLOSS EE 25 11 Appendix A TevisiOm DistOry cis cciyssciavssseastinsdvenceessgeecaasiusatecs sunecdensuedcans iden dotvsncceea Leaedaas Wuauecs aaecuanges 26 HL Manual revision history ices ves secavacecesaacescsdewausseedenvcuds AER 26 11 2 Protocol r yision DIStONY eisena suaecehasdequaes sue OR E ARTE AEN dE 26 113 Feat
12. alBx arms the dark calibration mode Flipping the switch triggers the dark calibration and modifies the calibration values in the unit Dark calibration is performed in a completely dark environment Check a reading to ensure that the period is correct after entering the dark environment it could take a few minutes to collect an accurate dark period A dark period of only a few seconds is too small The format of the response is 0 Z Calibration response is being returned 1 B Dark Calibration 2 a Armed 3 L L Locked Wait for unlock before calibrating after Arm command firmware upgrades are disabled U Unlocked Calibrate immediately after Arm command Enable firmware upgrade 4 5 Carriage return 0x0d Line feed 0x0a Table 5 Dark calibration response An example is zBaL 012345 Revision 1 2 Page 10 Last modified Jul 9 2011 Unihedron SQM LU Users manual 4 2 5 Disarm calibration command The Disarm calibration command zcalDx disarms calibration modes from being triggered by the unlock mode The format of the response is 0 Z Calibration response is being returned 1 x All calibration modes 2 d Disarmed 3 L L Locked Wait for unlock before calibrating after Arm command firmware upgrades are disabled U Unlocked Calibrate immediately after Arm command Enable firmware upgrade 4 5 Carriage return 0x0d Line feed 0x0a
13. booting and immediate use Firmware feature 13 D HHHHHHHHEX Set period in seconds for interval reporting to RAM for immediate use Firmware feature 13 THHHHHHHEX Set threshold in mag arcsec for interval reporting only to EEPROM and RAM for booting and immediate use Firmware feature 13 tHHHHHHHEX Set threshold in mag arcsec for interval reporting only to RAM for immediate use Firmware feature 13 Ix Request interval settings note upper case T Firmware feature 13 Table 1 Command summary Revision 1 2 Page 6 Last modified Jul 9 2011 Unihedron SQM LU Users manual 4 2 Response details 4 2 1 Reading request The Reading request rx commands the SQM LU to provide the current darkness value as well as all variables used to generate that result The format of the response is 0 r Indicates that a reading is being returned 2 8 06 70m Reading in magnitudes per square arc second Leading space for positive value Leading negative sign for negative value A reading of H Om means that the light at the sensor has reached the upper brightness limit of the unit 10 21 0000022921HZ Frequency of sensor in Hz 23 33 Q000000020Cc Period of sensor in counts counts occur at a rate of 460 8 kHz 14 7456MHz 32 35 46 0000000 000s Period of sensor in seconds with millisecond resolution 48 54 039 4C Temperature measured at light senso
14. esecsseeeeeeeeneeeeeenes 19 Revision 1 2 Page 2 Last modified Jul 9 2011 Unihedron SQM LU Users manual 1 Theory of operation The SQM LU measures the darkness of the night sky to provide readings of magnitudes per square arc second through a USB connection A light sensor TSL237 provides the microcontroller with a light level and readings from the temperature sensor are used to compensate the light sensor readings for various operating temperatures Commands sent from a PC through the USB cable to the USB interface are relayed to the microcontroller The microcontroller responds to commands by sending data strings to the USB interface which are then relayed to the PC Light sensor Temperature sensor Data Power Microcontroller USB interface Illustration 1 SQM LU block diagram 1 1 Quick start 1 Your computer must have the FTDI VCP driver installed You can get the most updated driver for your operating system from here http ftdichip com Drivers VCP htm 2 Ifyou are using Windows then download and install the latest Knightware SQM Reader from www knightware biz sqm Follow the instructions for installing and using that software 3 If you are using Windows Linux or Mac you can use the Perl scripts supplied on the CD Revision 1 2 Page 3 Last modified Jul 9 2011 Unihedron SQM LU Users manual 2 Specifications USB connection USB B connector 5m USB
15. ght calibration temperature An example is z 6 019 0C Revision 1 2 Page 14 Last modified Jul 9 2011 Unihedron SQM LU Users manual 4 2 9 Manually set dark calibration time period Calibration is done at the factory however in the case where calibration values must be restored or set to something else this command allows a new calibration value to be placed into the SQM LU Executing the command zcal7 x manually sets the light calibration offset to the value specified in The units are in seconds The format of the response is 0 Z Calibration response is being returned 7 Manual Set Light Calibration Offset 4 15 0000300 000s Value that was set into EEPROM 16 17 Carriage return 0x0d Line feed 0x0a Table 10 Response of manually setting dark calibration time period An example is Z 7 00000300 00s Revision 1 2 Page 15 Last modified Jul 9 2011 Unihedron SQM LU Users manual 4 2 10 Manually set dark calibration temperature Calibration is done at the factory however in the case where calibration values must be restored or set to something else this command allows a new calibration value to be placed into the SQM LU Executing the command zcal8 x manually sets the light calibration offset to the value specified in The units are C Note The SQM LU records the temperature in a raw
16. r in degrees C Leading space for positive value Leading negative sign for negative value 55 56 Carriage return 0x0d Line feed 0x0a Table 2 Reading request response An example is r 06 70m 0000022921Hz 0000000020c 0000000 000s 039 4C 0123456789 123456789 123456789 123456789 123456789 123456 Future revisions of this reading string will only modify reported values beyond position 54 Characters 0 to 54 may be considered stable Revision 1 2 Page 7 Last modified Jul 9 2011 Unihedron SQM LU Users manual 4 2 2 Calibration information request The calibration information request cx returns all data about the specific light sensor in the unit required for to calculate a reading The format of the response is 0 C Indicates that the calibration information is being returned 2 13 00000017 60m Light calibration offset in magnitudes per square arc second 15 26 0000000 00Qs Dark calibration time period in seconds with millisecond resolution 28 34 039 4C Temperature in degrees C measured during light calibration Leading space for positive value Leading negative sign for negative value 36 47 00000008 71m Offset of light sensor based on manufacturing category 49 55 039 4C Temperature in degrees C measured during dark calibration Leading space for positive value Leading negative sign for negative value 56 57 Carriage return Ox0d Line feed 0x
17. ure revision gt eegene eege san Waa a aan a ea Nee dees 26 Revision 1 2 Page 1 Last modified Jul 9 2011 Unihedron SQM LU Users manual Illustration Index Illustration 1 SQM LU block Dia crannies 55ec cis erg Kat egdefteggg Eege Edert 3 Uilustration 2 Prone and back GREEN 4 TUT Ce ene 20 Illustration 4 Example cover Cal reegen orbe eebe e Un lendis 21 Index of Tables Table T Command summary iesch 6 Table 2 Radia reguest TE SP edd 7 Table 3 Calibration information request TESPOMS i352 eege eege Ree eee hewn 8 Tabl 4 Light calibration REH eege ee Eeer 9 Table 3 Dark calibration TespOmse ine e a ER AE EA E EAA RERE GE NR Esi 10 Table 6 Disarm calibration TESPONSE 4 sccssexesucscesssvaccatavcseiansaesdieesstavevas saseuedssutecensdacduanaaven dee sdecestaweteusandes 11 Table 7 Unit information request TespONSe we cessccsssssscedaceveusreakystesescoeevalexssdeensubecsedaxey ea leuueaceadagecceussedeceedans 12 Table 8 Response for manual setting of light calibration offset ee eee esseceeeeeereeeneeceeceeeeeeneeenaeens 13 Table 9 Response for manually setting of light calibration temperature eee eee eeeeeeseceeeeeeeeeeeeees 14 Table 10 Response of manually setting dark calibration time period 15 Table 11 Response for manually setting of light calibration temperature eee eee ese eeeceteeeeeeeeeeees 16 able Te EE EE eebe Eege 17 Table 13 Response of viewing or setting interval reporting Darameterg cee eee e
18. value with different resolution so the reply back may not be exactly the same as the value sent The format of the response is 0 Z Calibration response is being returned 8 Manual Set Light Calibration Offset 4 9 019 0C Value that was set into EEPROM 10 11 Carriage return 0x0d Line feed 0x0a Table 11 Response for manually setting of light calibration temperature An example is z 8 019 0C Revision 1 2 Page 16 Last modified Jul 9 2011 Unihedron SQM LU Users manual 4 2 11 Setting interval reporting parameters For firmware feature 13 and above the SQM LU is capable sending timed interval reports Each interval report is the same as the reading request report except that the serial number feature 14 and above is attached at the end so that numerous reporting SQM LUs can be distinguished from each other The format of the interval report is 0 r Indicates that a reading is being returned 2 8 06 70m Reading in magnitudes per square arc second Leading space for positive value Leading negative sign for negative value A reading of H 00m means that the light at the sensor has reached the upper brightness limit of the unit 10 21 0000022921HZ Frequency of sensor in Hz 23 33 Q000000020Cc Period of sensor in counts counts occur at a rate of 460 8 kHz 14 7456MHz 32 35 46 0000000 000s Period of sensor in seconds with millisecond resolution 48 54 0
19. way from the elements A plastic dome is recommended This may reduce the incoming light by about 15 20 Because a covering will reduce the incoming light the resultant reading will be darker higher magnitudes per arcsecond value The offset determined by a simple light experiment should be subtracted from the reading A pending firmware edition will allow for built in manual offset Apply this subtraction offset as a negative value i e if you measured 16 60 outside the covering then 16 75 under the dome then an Revision 1 2 Page 20 Last modified Jul 9 2011 Unihedron SQM LU Users manual offset of 0 15 should be applied to all readings Uniform lighting condition Ce Weatherproof covering SQM LE Offset 16 75 16 60 0 15 Illustration 4 Example cover calibration 6 3 Cover maintenance Keep the covering clean of dust water ice and bird droppings Revision 1 2 Page 21 Last modified Jul 9 2011 Unihedron SQM LU Users manual 7 Default settings The FTDI interface has not been altered from its default There should be no reason to alter the FTDI chip settings The baud rate is defined by the VCP driver side when a terminal program connects to the SQM LU Revision 1 2 Page 22 Last modified Jul 9 2011 Unihedron SQM LU Users manual 8 Troubleshooting Reading too bright too hot inspect lens for IR filter Problem Cannot get a reading
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