
Gemini Users Manual 2
1.2 Features
1.2.1 Physical Features
The Gemini Astronomical Positioning System is a professional level computer-to-servo
device for controlling a German Equatorial telescopic mount (GEM). It consists of four
components: (1) A computer board housed in a flat aluminum panel box to be attached by
screws to the pier of your GEM mount; (2) A right ascension servo motor connected
mechanically to the mount's RA shaft, and electrically to the Gemini computer via a
cable; (3) A declination servo motor (identical to the RA motor) connected mechanically
to the mount's Dec shaft, and electrically to the Gemini computer via a cable; and (4) a
Hand Controller with buttons, switches, and an 16 character LED display connected to
the Gemini computer via a serial cable. A fifth component, though essential, is not
provided as part of the Gemini package. It is a 12 to 18 volt D.C. power source that may
be either a storage battery or a well-regulated power supply.
1.2.2 Operational Features
The following is a list and brief description of Gemini's operational features:
Setup Features
(a) Hand Controller Setup
The user chooses one of three movement control modes; they are (1) Visual Mode for
centering and slewing, (2) Photo Mode for centering and guiding, and (3) All Speeds
Mode for centering, slewing, and guiding.
(b) Mount Parameter Setup
The user selects the mount's tracking, slewing, centering, guiding and GoTo speeds, sets
a TVC value if any, trains and activates the Periodic Error Control (PEC) function,
selects the type of mount being used, sets safety limits for the mount's RA movement,
and sets the mount's home position for parking.
(c) Encoder Setup
If accessory RA and Dec axis encoders are installed, the user inputs their resolution, and
can test them or turn them on and off. Alternatively, end switches can be connected to
the encoder port and configured to physically limit the mounts motions.
(d) Alarm Timer Setup
The user can set a timer for an audible alarm to sound. The alarm can be turned on and
off. The buzzer can also be set to be silent.
(e) Date and Time Setup
The user inputs the current UTC date and time. Alternatively, the UTC date and time can
be automatically set by a GPS receiver in the Geographic Location Setup described
below.
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