Meade LX200 CLASSIC Uživatelský manuál stáhnout pdf (Strana 2)

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Figure 1. Use of the RS-232 port

do something, but some return information (e.g.,

current pointing position or OTA temperature) to

the external device.

Commercial software packages such as Meade’s

Autostar Suite, as well as shareware and freeware

applications (e.g., Cartes du Ciel, Iris and

GuideDog) can generate commands for the

LX200GPS, sent over the serial connection. For

instance, in Cartes du Ciel, a user can select an

object or point in the sky with the cursor, and

command the telescope to slew to that object.

Unfortunately, not all of the MTSCP commands

are implemented correctly in all versions of the

LX200GPS firmware. For instance, the command

:SBn# (where n is a single ASCII digit between 1

and 9) is supposed to set the baud rate of the

connection between the LX200GPS and the

external device. However, I have found that

issuing this command to a scope running firmware

1.6b destroys the connection with the telescope

(that had been working perfectly). Once this

command is issued, communication with the

telescope cannot be reestablished until the

telescope is rebooted by powering it off and on

again.

The MTSCP commands that are needed for

guiding applications are those that set the tracking

rate and slewing rate, and those that move or stop

the telescope. These are presented in Table 1.

Problems with MTSCP

As indicated by the fourteen-page listing of the

MTSCP offered by Meade, the command set is

robust, offering the opportunity to perform most

of the handbox commands remotely. If all

commands worked as they are described by

Meade, the MTSCP would be adequate for

developing guiding and autoguiding software.

Unfortunately, such has not been the case. Web

Dove, Dan Johnson, I and others have tested

many of the commands with firmware versions

1.6b, 2.0i and 3.0d and found that a number of the

commands either don’t work as they are described

in the MTSCP, cause complete loss of

communication with the telescope until it is

rebooted (power down and power up again), or

don’t work at all. Following is a description of the

problems that may affect guiding operations

(slewing and guiding commands).

East and West Movement Commands Reversed

In at least one firmware version (1.6b, I think), the

commands to move east or move west at the

current slew rate (:Me# or :Mw#) are reversed.

Commanding an eastward slew produces a

westward slew instead.

Increment/decrement Tracking Rate Doesn’t

Work

As described in the MTSCP, the commands :T+#

and :T-# are supposed increase or decrease the

tracking rate of the telescope. Based on a model

where a 60.0 Hz synchronous motor causes

perfect sidereal tracking, these commands are

intended to increase or decrease the tracking rate

by 0.1 Hz. In my testing of firmware 2.0i and

3.0d, these commands had no effect. In fact, none

of the commands below the horizontal line in

Table 1 have any discernable effect on a

LX200GPS running either firmware 2.0i or 3.0d.

Tracking Pauses After Slew Command

In versions 1.6b and 2.0i (and probably earlier

versions), there is a slight pause of the sidereal

tracking (the RA drive) immediately following

execution of the :Me# or :Mw# command.

The

pause is short, just a few hundred milliseconds.

Nonetheless, it causes an apparent eastward drift

of the target of several arcseconds. (This effect

has been described as “ruberbanding” because a

guide star behaves as if it is attached to a rubber

band stretched from the east side of the FOV.)

This is not a concern for visual use, but is a big

Because each :Md# command is followed by a :Qd#

command at the end of the intended slew interval, it is likely

that the pause actually follows the :Qd# command.

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