Unihedron SQM-LU User Manual
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Unihedron SQM-LU User Manual

Sky quality meter - lens usb
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Sky Quality Meter – Lens USB
SQM­LU 
User manual

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Summary of Contents for Unihedron SQM-LU

  • Page 1 Sky Quality Meter – Lens USB SQM­LU  User manual...

  • Page 3: Table Of Contents

    Unihedron SQM-LU Users manual Table of Contents 1 Theory of operation..........................3 1.1 Quick start............................3 2 Specifications............................4 3 Hardware connections..........................5 2 Software development..........................5 4 Commands and responses........................6 4.1 Commands............................6 4.2 Response details..........................7 4.2.1 Reading request........................7 4.2.2 Calibration information request....................
  • Page 4 Unihedron SQM-LU Users manual Illustration Index Illustration 1: SQM-LU block diagram...................... 3 Illustration 2: Front and back of unit......................4 Illustration 3: Housing..........................20 Illustration 4: Example cover calibration....................21 Index of Tables Table 1: Command summary........................6 Table 2: Reading request response......................7 Table 3: Calibration information request response..................8...

  • Page 5: Theory Of Operation

    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.

  • Page 6: Specifications

    Unihedron SQM-LU Users manual 2 Specifications USB connection USB B connector (5m USB 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 to be ±10%...

  • Page 7: Hardware Connections

    . 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 be determined at connection time.

  • Page 8: Commands And Responses

    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.

  • Page 9: Table 1: Command Summary

    Unihedron SQM-LU Users manual Command Description Reading request Calibration information request Unit information request (note lower case “i”) zcalAx Arm Light Calibration command zcalBx Arm Dark Calibration command zcalDx Disarm Calibration command zcal5##### Manually Set Light Calibration Offset ###x zcal6#####...

  • Page 10: Response Details

    Unihedron SQM-LU Users manual 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: Column Value Description Indicates that a reading is being returned.

  • Page 11: Calibration Information Request

    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: Column Value Description Indicates that the calibration information is being returned.

  • Page 12: Light Calibration Command

    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.

  • Page 13: Dark Calibration Command

    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 “zcalBx” arms the dark calibration mode. Flipping the switch triggers the dark calibration and modifies the calibration values in the unit.

  • Page 14: Disarm Calibration Command

    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: Column Example value Description Calibration response is being returned. All calibration modes.

  • Page 15: Unit Information

    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. 00000003 11-18 Model number (8 digits).

  • Page 16: 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-LU. Executing the command “zcal5########.##x” manually sets the light calibration offset to the magnitudes value specified in “########.##”.

  • Page 17: Manually Set Light Calibration Temperature

    Executing the command “zcal6########.##x” manually sets the light calibration temperature to the value specified in “########.##”. The units are ºC. 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.

  • Page 18: 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 “#######.###”.

  • Page 19: Manually Set Dark Calibration Temperature

    Executing the command “zcal8########.##x” manually sets the light calibration offset to the value specified in “########.##”. The units are ºC. 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.

  • Page 20: Setting Interval Reporting Parameters

    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.

  • Page 21: Interval Reporting Period Setting

    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.

  • Page 22: Interval Setting Response

    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: Column Example value Description Interval settings from EEPROM and RAM are being returned.

  • Page 23: Electrical Connection

    Cover calibration Since the SQM-LU 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).

  • Page 24: Cover Maintenance

    Unihedron SQM-LU Users manual offset of -0.15 should be applied to all readings. Illustration 4: Example cover calibration Cover maintenance Keep the covering clean of dust, water, ice, and bird droppings. Revision 1.1 Page 22 Last modified: Jun 18, 2011...

  • Page 25: Default Settings

    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.

  • Page 26: Troubleshooting

    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\...
  • Page 27 Unihedron SQM-LU Users manual Revision 1.1 Page 25 Last modified: Jun 18, 2011...

  • Page 28: Company Contact Information

    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 Revision 1.1 Page 26 Last modified: Jun 18, 2011...

  • Page 29: Glossary

    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.

  • Page 30: Appendix A - Revision History

    Unihedron SQM-LU Users manual 11 Appendix A – revision history 11.1 Manual revision history Revision Description Initial product release. Troubleshooting d specification addition 11.2 Protocol revision history Revision Description Initial SQM-LE product release. Interval report (reading) includes serial number at end. SQM-LE 11.3 Feature revision history...

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