Sky Quality Meter – Lens RS232 SQMLR User manual
Contents
1. 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 1 Page 16 Last modified Jan 3 2010 Unihedron SQM LR 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 LR Executing the command zcal8 x manually sets the light calibration offset to the value specified in The units are C Note The SQM LR 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 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 1 Page 17 Last modified Jan 3 2010 Unihedron SQM LR Users manual2. 4 2 11 Setting Interval reporting parameters For firmware feature 13 and above the SQM LR 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 LRs 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 0 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 54 039 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 Ox0a 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 1 Page 18 Last modified Jan 3
3. 2010 Unihedron SQM LR 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 LR 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 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 X note upper c
4. 5 00000017 60m Revision 1 1 Page 14 Last modified Jan 3 2010 Unihedron SQM LR 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 LR Executing the command zcalo t x manually sets the light calibration temperature to the value specified in The units are C Note The SQM LR 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 Light Calibration Temperature An example is z 6 019 0C Revision 1 1 Page 15 Last modified Jan 3 2010 Unihedron SQM LR 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 LR Executing the command zcal7 x manually sets the light calibration offset to the value specified in
5. Additional diodes may be used internally to raise this voltage range Example 4 diodes gives a voltage range of 8 17 8VDC 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 Unihedron Illustration 2 Unit photo Revision 1 1 Page 4 Last modified Jan 3 2010 Unihedron SQM LR Users manual 3 Hardware connections The SQM LR requires one connection to a RS232 port as well as DC power from the supplied AC adaptor The maximum length cable per the RS232 specification is 300ft 2 Software Development The SQM LR communicates as a standard serial port device Commands can be sent to the SQM LR using a serial terminal emulator to the serial communications port that the device is connected to Interface Program overview Data commands are sent to the SQM LR and it responds with a string of characters A connection must be opened to the serial port assigned to the SQM LR Revision 1 1 Page 5 Last modified Jan 3 2010 Unihedron SQM LR Users manual 4 Commands and Responses The SQM LR 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 A summary of all commands are
6. 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 1 Page 11 Last modified Jan 3 2010 Unihedron SQM LR Users manual 4 2 5 Disarm Calibration command The Disarm calibration command zca1Dx disarms calibration modes from being triggered by the unlock mode The format of the response is 0 Z Calibration response is being returned xX 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 Table 6 Disarm calibration response An example is zxdL 012345 Revision 1 1 Page 12 Last modified Jan 3 2010 Unihedron SQM LR 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 00000004 Protocol number 8 digits This will always be the first 8 characters after the i response This value indicates the revisio
7. temperature sensor are used to compensate the light sensor readings for various operating temperatures Commands sent from a PC through the RS232 cable to the RS232 interface are relayed to the microcontroller The microcontroller responds to commands by sending data strings to the RS232 interface which are then relayed to the PC Power Light sensor Microcontroller RS232 interface Data Temperature sensor Illustration 1 SQM LR block diagram 1 1 Quick start 1 Connect the SQM LR to your serial port using the supplied RS232 straight through 9 pin cable 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 or a serial terminal emulator set to 115200 baud to gather readings by typing rx Revision 1 1 Page 3 Last modified Jan 3 2010 Unihedron SQM LR Users manual 2 Specifications RS232 connection RS232 B connector 6ft 9 pin RS232 straight through cable supplied Physical size 3 6 x2 6 x1 1 Meter precision Each SQM LR is factory calibrated The absolute precision of each meter is believed to be 10 0 10 mag arcsec The difference in zeropoint between each calibrated SQM L is typically 10 0 10 mag sq arcsec Power requirement 19mA 5 2V 15 7VDC Note
8. 19 4 211 3 Interval setting TESPOMSE iii ridad A aida dana 20 AZAR TS AUG rate SUING rie 21 424121 Restoring the baud rate t gatle tensed eco 21 4 2 13 Baud rate Switch Stats iis cjescsvcsavasdavecoessceassuedisdacaconnpavaatasycanecessneeeda iar iii i esini i 22 5 Electrical conection pct inicios 23 Mecanica Installations oee A E E E Re DN E E a A ah RE de 23 OL COVE Select a E TEAR EE A O a e a AE TERASE I 23 6 2 Cov t calibrat A e e a as nce el alana e Coe aoea 23 6 3 Cover malntenante sisisi anpii erin an ai 24 O T E 25 o roubles hootinS nr en o de A 26 9 Company contact inform tion ossessi siiis ninia a a aa e i nii pin aaie 27 WOO S SEA Was es rcs a ic ne Cu erties ea E a a cs acd a a ates nal ase duds du esa EE EE E 28 Wy APPEROTEA Revision History ecne ennn Gacasies da 29 PGT Manual Reviston ITS CODY gcc cs e eaee ce ns a a bs sce svc Sega eaee aves 29 112 Protocol revision DIS LORY das iii 29 11 3 Feature revision Dti add ias 29 Revision 1 1 Page 1 Last modified Jan 3 2010 Unihedron SQM LR Users manual Illustration Index Illustration 1 SQM LR block MAT shsds cana tOtien aedasndecvdetesfechaancneeete 3 Tll stration 2 Unit PO Ss a 4 ISTMO O EE E EE A E E E 23 Illustration Example cover calor di oleo 24 Index of Tables Table 1 Command Summary ascii id italia 7 Table 2 Reading reg est response nannies ln a it iS 8 Table 3 Calibration information request response essesssesssseee
9. Sky Quality Meter Lens RS232 SQM LR User manual Unihedron SQM LR Users manual Table of Contents Theory Of Operational diab aida asian ain anode 3 Wed QUICK Starts cect E E coves ETE E E aos Lasse anek E E eas T A E Dleesat 3 Specifications ee re r a a a a a e cus nee who gehs 4 A ESE 5 7 SoftWare Development ect erosi e ee tis 5 4 Commands and Responses ninia tica ES e ESE ESE EE RT codes 6 A Commands Aea stes dd a a e te e os a do 6 AL RESPONSE eo o dr ld 8 4 2 1 REAdIME TEQUES En reis 8 4 2 2 Calibration information LEQUES atodos rl 9 4 2 3 biet Calibrati n Command A cleaver ee ese ad ene waa 10 4 2 4 Dark Calibration COMMON A RA 11 4 2 5 Disarm Calibration COMME ti as 12 4 2 6 Unit IO Manson 13 4 2 7 Manually Set Light Calibration DiiS dessa ns gus quvteowaeenezs 14 4 2 8 Manually Set Light Calibration Temperature oooonnnnnnnccnonnnonncnonnnanonono nono ncnonnnnnnnnnn cono ncnnncnnnos 15 4 2 9 Manually Set Dark Calibration Time PerlOd oooooonnncccnnnoccnoncccnonanononcnononccononoconnnocnnnnccnnnncnnns 16 4 2 10 Manually Set Dark Calibration Temperature oooococnnococnoncccnnnccnnoncnononcconnncnononononnncnconnccnnnnss 17 4 2 11 Setting Interval reporting Par dmMeer ss aa ieadcalsdeapuate vagy eeoaneevasaaqessseasss Qos anions 18 4 2 11 1 Interval reporting period IO A A a bit 19 4 2 11 2 Threshold setting for interval reportiNg cocnnocccnoncccnnaccnnoncnononanonnnanononccnnnnnnnnnnccnnn naciones
10. ase T sets the threshold of the timed interval reports to EEPROM and RAM for boot and immediate use Executing the command t i X 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 1 Page 19 Last modified Jan 3 2010 Unihedron SQM LR 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 00000003605 Interval period that was set into EEPROM 14 24 00003003605 Interval period that was set into RAM 26 37 00000017 60m Threshold value that was set into EEPROM 39 50 00000017 60m Threshold value that was set into RAM 51 52 Carriage return 0x0d Line feed Ox0a Table 13 Response of viewing or setting interval reporting parameters An example response is I 0000000360s 00000003605 00000017 60m 00000017 60m Revision 1 1 Page 20 Last modified Jan 3 2010 Unihedron SQM LR Users manual 4 2 12 Baud rate setting To change the baud rate with software submit the command baud x where is a 10 digit number repre
11. e for data retention In the SQM LR the parameters in the micro controller can be written 1 million times and last for 100 years SQM LR Sky Quality Meter with lens and RS232 connectivity RS232 Recommended Standard 232 used for serial data communication Revision 1 1 Page 28 Last modified Jan 3 2010 Unihedron SQM LR Users manual 11 AppendixA Revision history 11 1 Manual Revision history 1 0 Initial product release 1 1 Troubleshooting d specification addition 11 2 Protocol revision history Initial SQM LE product release Interval report reading includes serial number at end SQM LE E 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 SOM LE 13 Interval report feature added SQM LE 14 Interval report includes serial number 15 Baud rate setting for SQM LR Revision 1 1 Page 29 Last modified Jan 3 2010
12. fied Jan 3 2010 Unihedron SQM LR Users manual 7 Default settings The SQM LR comes with a factory default communication rate setting of 115200 baud This can be changed by software of set back to the default by an internal hardware jumper See section ____ for details Revision 1 1 Page 25 Last modified Jan 3 2010 Unihedron SQM LR Users manual 8 Troubleshooting Problem Reading too bright too hot Cause IR filter may have come loose Solution Ensure that you can see a blue coloured filter in the lens Problem Loss of communication Cause 1 Baud rate may have been changed 2 Wrong cable used Solution 3 Examine the baud rate settings on page 21 4 Make sure you are using a straight through cable for testing Revision 1 1 Page 26 Last modified Jan 3 2010 Unihedron SQM LR 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 Revision 1 1 Page 27 Last modified Jan 3 2010 Unihedron SQM LR 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 lifetim
13. l 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 LR is not weather proof it must be protected in some 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 Revision 1 1 Page 23 Last modified Jan 3 2010 Unihedron SQM LR Users manual 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 offset of 0 15 should be applied to all readings Uniform lighting condition AAA 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 1 Page 24 Last modi
14. n number of the data protocol to from the SQM LR The protocol version is independent of the feature version 11 18 00000005 Model number 8 digits The model value identifies the specific hardware model that the firmware is tailored for 20 27 00000014 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 0x0d Line feed 0x0a Table 7 Unit information request response An example is i 00000004 00000005 00000014 00000413 Revision 1 1 Page 13 Last modified Jan 3 2010 Unihedron SQM LR 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 a new calibration value to be placed into the SQM LR Executing the command zcal5 x manually sets the light calibration offset to the magnitudes value specified in 4444444 The units are OOO 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
15. o 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 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 1 Page 10 Last modified Jan 3 2010 Unihedron SQM LR 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 zca1Bx 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 B Dark Calibration 2 a Armed 3 L L Locked Wait for unlock
16. seen in the following table Revision 1 1 Page 6 Last modified Jan 3 2010 Unihedron SQM LR Users manual 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 zcal5 _ Manually Set Light Calibration Offset HHX ZCalo Manually Set Light Calibration Temperature HHX zCal7 Manually Set Dark Calibration Time Period HHX zCal8 Manually Set Dark Calibration Temperature HHX 0x19 Reset microcontroller see bootloader Hexadecimal value 19 a Intel Hex firmware upgrade initiation see bootloader PH HHHHHHX Set period in seconds for interval reporting to EEPROM and RAM for booting and immediate use Firmware feature 13 DHHHHHHH HX 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 tHHHHHHAFEX Set threshold in mag arcsec for interval reporting only to RAM for immediate use Firmware feature 13 Ix Request interval settings note upper case I Firmware feature 13 baud Change the baud rate HHEX Bx Return the status of the baud rate switch Table 1 Command summary Re
17. senting the delay value relating to the baud rate This delay value can be calculated as follows Delay 14 7456e6 4 Baudrate 1 For example to obtain the delay value for a baud rate setting of 9600 baud Delay 14 7456e6 4 9600 1 383 Therefore the command is baud0000000383x There is no response to this command because the unit will have changed baud rate and an instant response to your computer will be unreadable You must reopen your serial communication connection at the new baud rate By default the SQM LR is shipped with the ability to accept baud rate changes A jumper on the circuit board can be used to force the baud rate to 115200baud after power up See the next section for using this jumper 4 2 12 1 Restoring the baud rate In the case where the unit may not be communicating you can force the baud rate to 115200baud as follows 1 Remove the power and data connection from the unit 2 Open the unit by removing the bottom 4 screws Be careful not to allow the lens or lens plate cover to fall out or get dirty 3 Position the jumper block over the 115200 jumper pins 4 Test the communication by reconnecting the power and data then open a serial communication link at 115200 baud and type in the rx command Revision 1 1 Page 21 Last modified Jan 3 2010 Unihedron SQM LR Users manual 4 2 13 Baud rate switch status To determine the status of the baud rate switch without opening the
18. sers 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 000s 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 0x0d Line feed Ox0a 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 1 Page 9 Last modified Jan 3 2010 Unihedron SQM LR Users manual 4 2 3 Light Calibration command Calibration of the SQM LR 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 t
19. ssresseessersseeessetsssressttsseesseeesseeesseesseesst 9 Table 4 Light Calibration response sssesseessesssesssesesseeessresseessersseeessteesseesseesseesseeessseesstesseesseesseeeessets 10 Table 5 Dark Calibration response tai ini 11 Table Gs Disarm calibration response drn o ao 12 Table 7 Unit information request TESPONSE rs 13 Table 8 Response for Manual setting of Light Calibration OffS t oooooncccnnncccnoncccnoncccnnncnonnnnncnnnncnnnnnnos 14 Table 9 Response for Manually setting of Light Calibration Temperature oooocnnccnnnnnnonononnnonnnonnncnnncnnno 15 Table 10 Response of Manually setting Dark Calibration Time PeriOd ooonnccnncninnnnnocononcconnnonnncnnncnnos 16 Table 11 Response for Manually setting of Light Calibration Temperature oooconnncnnononoccnnoncnoncnannnnnnno 17 Table 12 Interval report ui daran aida aretes cie 18 Table 13 Response of viewing or setting interval reporting parameterlS oooococnoncccnonccnnoncnonnnccnnnnccnanancnns 20 Table 14 Response of viewing or setting interval reporting parameters ooocooccnnonnnocononnnonncnnnncnnncconcnnnnos 22 Revision 1 1 Page 2 Last modified Jan 3 2010 Unihedron SQM LR Users manual 1 Theory of operation The SQM LR measures the darkness of the night sky to provide readings of magnitudes per square arc second through an RS232 connection A light sensor TSL237 provides the microcontroller with a light level and readings from the
20. unit the Bx command can be sent The response is as follows 0 0 O is returned when the jumper is OFF This position indicates that the baud rate can be changed in software as described on page 21 1 is returned when the jumper is ON This position forces the SQM LR to 115200 baud after power up or reset 1 2 Carriage return 0x0d Line feed Ox0a Table 14 Response of viewing or setting interval reporting parameters An example response is 0 Revision 1 1 Page 22 Last modified Jan 3 2010 Unihedron SQM LR Users manual 5 Electrical connection An AC DC adaptor is provided The SQM LR uses a voltage regulator to bring the incoming DC voltage down to 3 3VDC The lowest voltage at the input should be 4 5VDC 3 3 1 2VDC For remote applications a deep cycle Lead Acid 6VDC battery can be used The SQM LR unit is NOT protected against over voltage above 15V The SQM LR unit is protected against reverse polarity connection 6 Mechanical Installation Unihedron sells an enclosure that is suitable for mounting either the SQM LR 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 wil
21. vision 1 1 Page 7 Last modified Jan 3 2010 Unihedron SQM LR Users manual 4 2 Response details 4 2 1 Reading request The Reading request rx commands the SQM LR 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 O 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 54 039 4C Temperature measured at light sensor in degrees C Leading space for positive value Leading negative sign for negative value 55 56 Carriage return 0x0d Line feed Ox0a 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 1 Page 8 Last modified Jan 3 2010 Unihedron SQM LR U
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