Gemini's New Features in Level 4

Gemini Supports Custom Mounts

The user can setup the gearing parameters of his mount: the gear ratios and direction of spur gear and worm gear and the servo motor encoder resolution. The step resolution can reach from a tenth of an arcsec per step (servo motor encoder tick) up to 2.5 arcsec/step. Resolutions can be set independently for RA and DEC axes.

With this new feature, Gemini can be retrofitted to many German Equatorial Mounts, f.i mounts with 359:1 Byers gears, Vixen or Astrophysics mounts. Existent servo motor/encoder combinations can often be used, eliminating the need for mechanical adapting the Gemini motor assembly, but custom cables will be necessary.

These data can be set under the Setup->Mount Parameters->Mount Type menu point with the new mount type selection "Custom Mount". Selecting this type, the submenus "RA Spur:", "RA Worm:", "DEC Spur:", "DEC Worm:", "RA M.Enc:" and "DEC M.Enc:" are accessible. Only integer values are accepted. Directions can be selected by setting the sign of the worm gear ratio.

Remote Hand Controler functionality

Gemini can now be used without the hand controler being attached. All outputs and button presses can be routed over a serial channel. A HC emulation is available for PDAs or for aftermarket software like the GCC.

A second serial channel is available

The DB15 HC port can be equipped with aftermarket adapters to work as a second serial line. Adapters can be made for RS232, USB devices, Bluetooth, Ethernet or WLAN. This second serial line works indepentendly form the standard RS232 port and can be used for HC emulation or PC control.

Supporting the Horizontal Coordinate System

The new Level 4 software supports the usage of horizontal, that means Azimuth and Elevation coordinates. These coordinates can be used for queries and GoTo operations over the serial line (see Serial Command Set below) as well as by means of the hand controler.

The HC main menu item "RA/DEC Coord." is now called "Coordinates" and contains the additional submenu items "Az/El Display" and "Enter Az/El".

Selectable Serial Port Transmission Rates

Gemini L4 allows to set several transmission rate values for the serial (RS232) port, from 4800 up to 38400 bit/s, under the Setup->Communication->RS232 speed menu point. The default value is 9600 bit/s.

Selectable GPS transmission rate

The GPS speed can be set to 4800 or 9600 bit/s using Setup->Communication->GPS Rx speed menu point. The default value after a reset is the standard NMEA 0183 speed of 4800 bit/s.

By setting the GPS receiver transmission rate, Gemini's startup process is accelerated, because the other rate doesn't have to be probed. Also, the query result message display can by interrupted by pushing the menu button.

Reduced Main Menu point selection available

After having set up Gemini and aligning the telescope or building a pointing model, some of the menu points are rarely used. The new "Reduced Menu" mode only displays the main menu items mainly used while observing: Object Database, Show Information, GoTo, RA/DEC Coordinates and Identify while scrolling downwards (with the DEC- button). Scrolling upwards with DEC+, Align Telescope is additionally included to allow to refine the pointing model. The other main menu items, Setup, Object Search, Show Date/Time and GuideTo are suppressed. At any time it is possible to switch back to Full Menu Mode using the Quickmenu feature.

Redesigned Quick Menu selection

To accelerate the Quick Menu access and to offer more selections the Quick Menu feature was redesigned:

Parking the OTA

The telescope can be parked at any "Home Position" by either the hand controller or serial control. The home position defaults to the CWD (Counterweight Down) position.

Even after setting the Home Position, parking at the CWD position is still possible since this option is offered as an additional menu point in the Quick Menu and available as as serial line command (:hC#).

Further, the Quick Menu allows to stop tracking at any arbitrary position. For example, after pointing the OTA downwards to stop dewing.

More Alignment Stars, with Proper Motion taken into account.

The number of Alignment Stars has been extended to 49. Especially more southern hemisphere objects are now included:

The coordinates of these stars are stored with subarcsecond precision. Since some bright nearby stars have a significant proper motion these motion values are also stored and included into the calculation to achieve highest alignment accurateness.

Extended Serial Line Protocol

The Level 4 serial command set was extended not only to reflect the additions for new and custom mounts, but also includes commands necessary for dome control and other operations. :GA# and :GZ# commands are supported to query the azimuthal coordinates. The hour angle the mount is pointing at can be obtained using the new :GH# command. The side of the mount the OTA is can be asked for with :Gm while :GS# now delivers the sidereal time.

Extended Identify interface

The interface to the Identify function within Gemini was extended to remember the results of the latest Identify run. Now the user can decide to use

Extended Safety Limits Handling

The physical positions of the Safety Limits are automatically derived from the mount settings. They default to 114 degrees on the left (motor) side and to 123 degrees on the right side, with respect to the startup (CWD) position.

To avoid accidentely setting the safety limits, another submenu point "Confirm to Set" was added as a submenu of "Setup->Mount Parameters->Set Safety Limits".

Additionally, a second submenu point "Reset to Defaults" was introduced there to allow to reset only the Safety Limits to their default values (both left and right) without having to reset all the other Setup values.

Selectable PC Synchronization Behaviour

Gemini accepts two different kinds of Sync commands over the serial line. The LX200 protocol :CM# command shifts the internal coordinate system to reflect the latest position correctly, "Synchronizing" it to an object. On the other hand, the additional ":Cm# command uses the detected positional difference to enhance the internal pointing model. The software running on a connected computer can choose between both.

Since there are still some software packages on the market not supporting the Additional Align feature, Gemini's software now allows to set the way :CM# and :Cm# commands are interpreted. The Setup->Communication menu point now contains a "Sync or Align" submenu. "Sync Only" selects Gemini's standard behaviour as described above, while "Sync <-> Add. Al." swaps the functionality of both commands, allowing to enhace the pointing model even with PC software not supporting this explicitely.


PEC data can be up- and downloaded

The number of PEC guiding pulses can be limited.

Pulse Guiding

There is an additional guiding possibility available: moving a predefined distance or time. It is offered in 3 varieties:

Alternatively used Encoder Port

Over the years, only a small percentage of Gemini users connected axis encoders. Axis encoders are now set offline by default. The 4 digital (TTL) inputs bits can be used alternatively to connect to custom hardware. Their state can be checked and set using the extended serial line protocol.

This feature adds additional possibilities for an unattended robotic telescope, f.i. by adding end switches.

Last modified: Nov 09, 2005