HandyAvi® - Meade® Telescope Control Tutorial

If you have a Meade® telescope and it is connected to your computer by an RS-232, i.e., Serial cable, you can use the "Telescope Controls" to control the telescope. Most new computers do not have an RS-232 connector so we use a USB/Serial adapter cable that plugs into a USB port on our computer and provides an RS-232 connector that can be connected via a cable to the telescope. There are many inexpensive USB/Serial adapter cables available for purchase on the internet.

Before attempting connection for the first time, you should select the proper COM port by selecting the HandyAvi menu item "Tools" and the subitem "Telescope Port...". If you have a COM port, it will appear in the pull-down item. Select the COM port that is connected to the telescope.

The telescope can then be connected either by clicking the "Display telescope controls" checkbox or by using the HandyAvi Tools menu submenu "Telescope Controls...

After connection is established you will see the LX-200 Controls panel.

First Telescope Tab - LX-200 Controls


First Telescope Tab - LX-200 Controls

The above image shows what you will see if the telescope port is working and the telescope is communicating properly with HandyAvi. If everything is "well" the RA and DEC fields will contain numbers. If the telescope is not responding for any reason, the RA and DEC fields will be blank.

Note that the telescope control window is a "modeless dialog window" so it can be left up and operated in concert with the camera controls.

Also Note that we currently have the telescope in "park" mode as described below.

Coordinates Section

"GET" gets the current RA and DEC from the telescope and displays them.

"GO" goes to the RA and DEC that are shown in the RA and DEC edit boxes. NOTE that the formats must be exactly as shown. You can enter any valid RA and DEC and then press "GO" and the telescope will slew to that position.

"HALT" stops the telescope motion immediately in case you notice that your camera is going to be crunched by the fork arms or your cables are stretching too much, or you simply change your mind about slewing to the selected coordinates.

Motion Section

The speed can be set to any of the four indicated Meade telescope-slewing speeds.

The NORTH, SOUTH, EAST and WEST push buttons are operated by using the left mouse button. These buttons work just like the buttons on the Meade keypad, i.e., the telescope will move in the direction indicated while the button is held down. Motion will stop when the button is released.

After motion has been completed, the coordinates are updated and displayed.

Park Section

The "Park" feature allows you to park the telescope i.e., holds it motionless. It does this by turning on guide mode then automatically holding the "East" button down. This stops the guide motor completely so that the telescope stops tracking the sky. Why use park?  If you want to leave the telescope set up for days on end so that you do not have to realign it every night, the Park mode prevents the cords from wrapping around the telescope as they would if the telescope continued tracking.

There is a time field so that you can "Park the telescope in 7200 seconds" for example.

When you click the Park box so that it is checked, HandyAvi will look at the time field and count down to zero before parking the telescope. If the time field is 0 or reaches 0 after counting down, the telescope will park immediately.

Normally, you would enter the time first then cause the Park check box to be checked.

When you uncheck the Park box, the telescope is placed in guide mode, the East button is released and the telescope again starts tracking the sky.

During "Park" the speed change buttons are "grayed out" (disabled) and the "Go" button is disabled but all other controls function normally so you can, for example, change focus or get a read-out of the telescope's RA and Dec.

The "Park" setting is remembered by HandyAvi. If you had it set when you exited HandyAvi, it will be set when you reenter HandyAvi.

If the telescope was parked, it will continue to be parked even if you exit HandyAvi.

Focus Section

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  Focus Control

This section allows you to operate the standard Meade focusing motor.

There are two basic focusing speeds, "slow" and ‘fast". You can choose which speed you are using by checking or un-checking the check box. (Experience has shown that during slow speed runs, the motor often bogs down and stops so use of the fast speed might be necessary.)

There are two "Stepped" modes (Slow - Stepped and Fast – Stepped) that allow you to use the Meade focuser in a much more controlled manner. When "stepping", HandyAvi transmits a motor-on, motor-off command of fixed duration.

If you hold the "IN" or "OUT" button down, the telescope will execute a series of stepped motions.

Step mode is highly recommended if you are using a standard Meade focuser with the LX-200.

Again, the counter attempts to indicate position. Each "step" provides a count of 2. This was to try to get a correlation between stepped and un-stepped focus position. Not entirely successful.

Note that the Meade focusing motor is not a stepper motor so it is almost impossible to tell accurately what the focus position is.

The two buttons, "IN" and "OUT" determine which direction the focusing motor is moving the eyepiece. They operate in the same manner that the NORTH, SOUTH, EAST, and WEST buttons do, i.e., the motor will run as long as the button is held down. The motor will stop when the button is released. Note that the button that was last pushed stays a little grayer than the other button. This will help you remember which direction you were going as you attempt to focus at 2:00 AM when your brain has shut down and the image download time (of certain CCD cameras) puts you to sleep while attempting to focus.

The counter attempts to show the position of the focusing control. The motor seems to take about one second to reach full speed in the "fast" mode. The motor seems to coast to a stop over a period of about three seconds if it was going at full speed. The algorithm HandyAvi is using does a simple linear interpolation using those numbers as an approximation. When a button is pressed, the PC time clock is accessed and the value is stored. When the button is released, the time clock is again accessed and the difference is taken yielding an elapsed time value accurate to 1 millisecond. The counter is based upon these elapsed times and the motor acceleration/deceleration values. More work on measuring acceleration/deceleration rates might make this more accurate but, at the moment, you should consider this number only a rough guide. It is very unlikely to provide accurate positioning information.

Once focus is achieved, the counter can be set to zero to provide at least some sense of where the focus position is/was.

There are two other focus types, "Slow Stepper Motor" and "Fast Stepper Motor". These are designed to accommodate a do-it-yourself stepper motor that is being used by the author of this section of the HandyAvi system. The Meade focus motor port on the LX-200, labeled "Focuser", puts out +19 Volts or -19 Volts depending upon which direction the Meade standard DC focusing motor should run. These voltages can be used instead as signals to control a stepper motor designed to replace the Meade DC motor. With a stepper motor, the focusing is precise and the counter will be completely accurate. (Newer Meade telescopes might have different focusing systems.)

Dynamic Focus Section

As the temperature drops, the telescope will shrink and the focus position will change… The Dynamic Focus control allows you to automatically compensate for the shrinkage by stepping the telescope focus any desired number of steps per hour.

Second Telescope Tab - Set Location, Time, Backlash and Tracking rate

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Location, Time, Backlash and Tracking rate settings

The above image shows the" Location and Time, Backlash, Tracking Rate" controls.

When one switches from "LX200 Controls" or "Objects" or "Sky Flats to "Location and Time, Backlash, Tracking Rate", the "Get" operation  of the first tab is automatically performed.

Telescope Location Section

Enter the coordinates of the current location of the telescope into the telescope. Type in the Latitude and Longitude then press "Set" to set the telescope's location into the telescope's internal memory.

Date Section

Enter the current date. Pressing "Set" then enters the data into the telescope. NOTE: Whenever "Set" is pressed, the telescope updates the planet positions. Mercury's position changes significantly from day to day so if the telescope is left set up for more than one day, pressing the "Set" button in the "Date" area will cause the planet positions to be updated and will allow Mercury and Venus in particular to be accurately found.

Time Section

Displays the current time and is updated every second by querying the telescope and displaying the results.

A new Local time can be entered in the edit box and then when "Set" is pressed, it will be entered into the telescope. HandyAvi also computes the corresponding sidereal time and enters that into the telescope also.

There is about a 1 second delay for the time setting operation so press "Set" one second early if you want to be within a second. Part of the delay is simply transmitting the data to the telescope.

Dec Backlash Section

The LX-200 has a Dec Backlash setting that can be from 0 to 100. The LX-200 software will not respond to this being set by HandyAvi but the newer GPS scopes will.

Tracking Rate Section

The LX-200 also has a Tracking Rate setting that can be set at a rate to track the Moon among other things. (The Moon moves slowly but noticeably against the background stars. If you are making images of the Moon, you might want to track it at the proper rate.) Again, the LX-200 software will not respond to this being set by HandyAvi but the new GPS scopes will.

Third Telescope Tab - Objects

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Objects tab

The above image shows the "Objects" tab.

Object Section

 Choose a catalog as shown below:

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Then enter an object number

"Get" will get the coordinates of the object and display them

"Go To" will cause the telescope to display the coordinates of the object and begin slewing to the object. Note that if you type in a number for an object that does not exist, the only indication will be that the RA and DEC will not change.

Note that the coordinates provided by a "Get" command are retrieved from the Telescope's data base.

Halt:  

Immediately stop the telescope's motion.

Sync:   

Causes the telescope's internal coordinate system to synchronize with the selected objects. (If your telescope is aligned and you somehow lost sync due to a power-off for example, you can locate and object in the sky, point the telescope at it, use the Object controls to select the object, "Get" its coordinates and then press "Sync". The telescope will now be able to use its internal coordinate system to go to other objects.)

About the catalogs

Note thathe catalogs are the ones stored in the Meade LX-200 telescope. They are:

List button  

Brings up an object list consisting of the Meade LX-200 guide stars followed by the NGC object catalog.

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Object list

This list is merely for convenience. Selection of an item does not currently drive the telescope.

Fourth Telescope Tab - Sky Flats

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Sky Flats Tab

Astronomers using CCD cameras designed for deep-space work often require frames called "Flats" which can be used to counteract tiny imperfections and dust particles within the optics train. There are several methods of making flats including constructing a light box, covering the scope with a tee shirt, etc. One method is to take a "sky flat". This is done typically during twilight. Frames are taken of empty sky and the background sky brightness is captured and the dust particles become visible in the captured frame. The captured frame can be used later to subtract out the dust particle contribution to images of deep-space objects.

The difficult part of taking sky flats is that the sky is not empty of stars and twilight may not last long enough. HandyAvi contains an algorithm for making sky flats.

To take sky flats:

Use the first tab (LX-200 Controls) to point the telescope at a region of the sky containing as few bright stars as possible. Set the Milliseconds field to the length of time that the telescope should move in "Center" mode.

The "Start" button sends a command to the telescope to set its speed to "Center" (as opposed to "Guide", "Find", or "Slew" speed).

The telescope will then move North, then East, then South, then West, then North, etc.

Each move will be for the number of milliseconds that were entered in the "Milliseconds" field. This will trace a square in the sky. The purpose is to cause the star background to move quickly so that the stars, if they are dim enough, will not leave visible trails. This will allow a sky-flat to be taken either during twilight - or anytime from light-polluted skies :-).

the "Stop" button stops the telescope's motion and returns its speed to "Guide" mode.