Last updated: 25 May 2006
Subject:	LNT Summary Update
Sent:	Thursday, May 25, 2006 11:18:51
PE Series LNT Q&A Summary
What is the LNT?
It is an electronic module that provides several related 
functions intended to reduce required user input during AutoStar 
initialization and `scope alignment:
1) A battery powered clock to provide time/date, similar to 
    an internal PC clock;
2) Sensors to automatically detect Level and North;
3) A SmartFinder, consisting of a lens, LED, and optical fiber
    that projects a dot onto the lens.
It is securely attached to a bracket that is mounted on the OTA, 
with a cover that holds the SmartFinder lens and optical fiber.
The cover is attached with spring-loaded screws that allow it to
be adjusted to align the SmartFinder with the 'scope optical axis.
How does the LNT work?
The module has a serial data interface with the AutoStar via the 
`scope wiring thru the HBX port, and is powered by the `scope 
power source.  The clock has its own battery and maintains time 
when the power is turned off.  The sensors are an array of 
accelerometers and magnetometer that can determine orientation 
with respect to the Earth.
When power is applied, the AutoStar goes through its own 
initialization, including checking whether or not an LNT is 
present. If so, the AutoStar will;
1) Download and store the current time/date from the clock.  Note 
    that once time is loaded from the LNT, the AutoStar maintains
    its own clock and no longer uses the LNT clock while powered on;
2) Modify the menu tree to include LNT functions and options.
If the Auto align option is selected, Autostar performs the following;
1) Initialize the sensor array;
2) Drive the OTA until data from the sensors indicate it has 
    detected North in the horizontal  plane, and the point where it is
     perpendicular to the gravitational field, relative to the center of
     rotation of the array.  In the absence of other influences, this would
     be Level and Magnetic North relative to the Earth;
3) Correct the data for True Level and True North using 
    previously stored values and save the results for the current 
4) Drive the OTA in the AZ axis while monitoring any variation of 
    Level and calculate a Tilt coefficient, then save the result 
    for the current session;
5) Determine the position of the AZ full CCW stop, which was initially
    set by the user, relative to North; this is used to determine which
    way to slew without hitting a stop during GOTO's;
6) Turn on the SmartFinder dot and proceed with a standard 
    alignment with star positions calculated using parameters from 
    the preceding steps and stored site information;
7) When alignment is completed successfully, turn off the Dot. 
 & nbsp;  Any corrections obtained will be temporarily saved in the 
    AutoStar for the current session.
NOTE: If Autostar does not detect the LNT clock, it will default
to 8:00PM on the last date that was set and request user input.
Most of the LNT functions will not be available, with the possible
exception of the Smartfinder dot.  The most common cause, besides
outright failure, is a dead or dislodged LNT battery.  See Appendix D
of the Manual for info on replacing it.
From this point on the LNT serves no purpose except to turn the 
Dot on and off via the AutoStar "0" (Light) key. Note that any 
corrections determined during the process are only saved for the 
current session. When power is turned off, they are lost unless 
a Park Scope is used.  The only semi-permanent corrections are 
those obtained during Calibrate Sensors, which are saved until 
the AutoStar is Reset, or the Calibration is performed again.
What are the advantages of the LNT?
1) The user only has to set the internal clock once, the first 
    time the system is used.  After that, the AutoStar will have 
    the correct time whenever power is applied.  It should be 
    remembered that the internal clock will have some drift, 
    similar to a PC clock, and should be checked/reset 
    periodically for really accurate time;
2) Physical setup of the telescope is much less critical.  There
    is no defined "Home" position as with the AT series. Since 
    the LNT will determine Level and Tilt, the mounting surface or
    tripod head and OTA need not be perfectly level.  Also, 
    orientation of the base can be somewhat arbitrary. I suggest 
    the base be oriented so the full CCW stop is somewhere on 
     the West side. This is so the LNT does not detect the South 
    magnetic pole and give a false null as it slews CW during 
    initialization. This has caused problems in some versions of 
    the Autostar firmware.
3) The SmartFinder provides a much larger FOV, but no magnification,
    so star alignment is somewhat simplified.
Does the LNT have any disadvantages?
Although the concept of the LNT is good, its implementation 
leaves something to be desired, especially the SmartFinder.
1) In the original version of the LNT, the optical fiber that 
    projects the Dot onto the lens was not always oriented 
    properly so the Dot wasn't visible.  A later version appears to
    be a bit better, but its position is still not very precise and there
    may not be enough adjustment to align the Finder.
2) Also in the early version, the Lens could be easily inserted 
    the wrong way, so again no Dot was visible.  This also was 
    corrected in the later version but the position of the fiber 
    can still cause problems;
3) The SmartFinder Lens is very susceptible to external forces.
    A small bump can disturb the alignment and a sharp blow can
    break it off.  I also understand it will not fit into a standard Meade
    hard case without modification of the insulating foam;
4) The SmartFinder requires an on-axis eye position as opposed 
    to the right-angle view finder on the AT series, and there is 
    some parallax shift;
5) The LNT mounting bracket interferes with proper installation 
    of the LPI camera so it can only be inserted +/- 90 deg. or a 
    full 180 deg. from the normal position.  The resulting image 
    on a PC screen can be confusing;
6) A shortcoming, rather than a disadvantage, is that the 
    Instruction Manual for the PE gives no comprehensive 
    instruction as to the prerequisites for using the LNT for the 
    first time, and there are several:
a) The local time/date/daylight saving should be set accurately;
b) The observing site lat/lon/time zone must be set; these value s
    are used to provide approximate correction for local magnetic
    deviation, which can be as much as 20 degrees depending on 
    geographic location;
c) A Motor Calibration and Drive Training should be 
d) Calibrate Sensors must be performed.  The previous steps 
    should be completed first, since they all affect the 
    accuracy of values obtained during the procedure.  These 
    values will become correction coefficients used after the LNT
    determines local Level/North.
After all the preceding setup steps are complete, scope power
should be cycled off/on and time/date/site location parameters
verified. There have been several reports of Autostar "forgetting"
the values when shut down.
If a reasonable amount of care is taken during the setup steps,
GOTO errors should be minimized.
Please note I am not affiliated with Meade and the preceding info was
determined entirely through my own analysis.  Any corrections and/or
additional info on the subject will be welcome and appreciated.
Regards to all,
Mike Hogan

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