GEM and Celestar 8 Hand Controllers
                                   

Hand Controller Project

This webpage documents construction of a hand controller for a homemade GoTo German equatorial mount (see the Large GoTo GEM Webpage). Instructions and wiring diagrams are provided to make this hand controller compatible with the Celestron Celestar 8 mount. The design requirements were to build a hand held control box with momentary push buttons for GEM drive motor direction and speed control. The total cost was about $10 and the project required a single afternoon.

Hand Control Box

The hand controller box is constructed from 3 mm transparent polycarbonate hobby plate and is 5 cm x 10 cm x 2.2 cm. I first glued the side pieces together with two component epoxy, forming two "L" shaped sections. It worked best to clamp the pieces onto a square dowel rod to give perfect right angle corners (below left photo). After the two "L" shaped side sections were completed, I glued them together to form a box (below right photo).

     

The basic control box parts are shown in the below left photo. The top and bottom are also constructed from 3 mm polycarbonate plate. I drilled 5 holes into the top plate to accept the momentary push buttons. I cut four 16 mm sections of 6 mm O.D. aluminum tube and threaded them to a M4 thread.  The threaded aluminum tube was epoxied into each corner of the side section box (below right photo) to accept the M4 machine screws that secure the top and bottom sections.

  

Wiring

The electrical components are 5 momentary push button switches, scraps of wire, and an 8 conductor coiled electrical wire. All electrical connections were soldered and insulated with heat shrink tubing. The electrical schematic is shown below. The four top buttons control the RA motors (white and green leads) and Dec motors (black and red leads). The fifth button (orange lead) controlls the speed. There is a common ground line (yellow) that runs through all 5 pushbutton switches. Closing any switch makes an electrical connection between the ground line and the particular motor function controlled by the switch.



The Completed Hand Controller

The completed hand controller is show in the below photos. Adding a RJ12 modular jack would make this controller compatible with the Celestar 8 mount (see the next web page section).
 

Celestar 8 Compatible Hand Controller

Before I give the Celestar 8 hand controller wiring diagram, here comes the usual warning: There is always a risk of damage with any home repair and maintenance of commercial equipment. It is always recommended to contact the manufacturer prior to performing any maintenance as this may void warranties and alter equipment performance. I assume no responsibility or liability for any damages resulting from what you may do to your own equipment. Anything you do is at your own risk, so be sure you know what you are doing and accept all risks prior to beginning.

Since the Celestar 8 hand controllers are becoming difficult to find, the following information may be useful to anyone wishing to build a Celestar 8 compatible hand controller. The Celestar 8 hand controller is a basic switch box with 4 momentary push buttons (below left photo), connected via a 6 conductor cord with a RJ12 modular jack (below right photo). The top and bottom buttons control the + Dec and - Dec, respectively. The right and left buttons control the + RA and - RA, respectively.

   

I traced the circuitry on my Celestar controller using a multimeter with a continuity setting (below left wiring diagram). I have drawn the wiring diagram using the same wire colors as are on the original Celestron RJ12 modular jack (below right photo). There is a common ground line (yellow) that runs through all 4 pushbutton switches. Closing any switch makes an electrical connection between the ground line and the particular motor function controlled by the switch. Note that only 5 of the 6 conductors are used (the blue wire is not used). The below diagram agrees with the Celestar 8 drive base socket wiring I found on the following website: Celestar 8 Hand Controller/Meade Pictor CCD Wiring Summary.

 

I have tested the following information by wiring my GEM hand controller to a RJ12 modular jack and it successfully controlled the Celestar 8 mount. Wiring a Celestar 8 compatible hand contoller is pretty easy. Construct a box with 4 push button switches and wire them as shown in the above Celestar 8 hand controller wiring diagram. The following RJ12 pin order is as shown in the above right photo (where the RJ12 conductors face toward you and the small plastic tab faces away):
1st pin from the left (white) connects to the + RA switch                       
2nd pin from the left (black) connects to the + Dec switch                      
3rd pin from the left (red) connects to the - Dec switch                          
4th pin from the left (green) connects to the -RA switch                          
5th pin from the left (yellow) is the common ground line to each switch    
6th pin from the left (blue) is not used                                                     

Be absolutely sure to connect each pin correctly. The blue (unused line) connects to a 5V line in the drive base socket. Incorrectly sending this line to one of the push buttons and back to the drive electronics could cause serious damage to the electronics!

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