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 flat 

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 flat 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 encoders are installed, the user inputs their resolution, and can 

turn them on and off. 

(d) Alarm Timer Setup 

The user can set a timer for an audible alarm to sound.  The alarm can be turned on and 

off.  

(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. 

(f) Restore Default Function 

The user can restore all setup items to their default values. 

Gemini Users Manual 

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