Nexstar 60GT Telescope

© Brooke Clarke, N6GCE 2003



Tasco 60

Background

I wanted to check out what can be seen from locations near my house that's surrounded by trees up to 100 feet tall.  This Tasco StarGuide 60 scope was on eBay for $60 in a fixed price sale.  It is the same as the Celestron Nexstar 60GT scope except it has the manual 6 button hand controller, not the Go To hand controller.  The GT in the Celestron model number means Go To.

This scope is part of a family of scopes called the little or baby Nexstars.  The scopes are the:

Hand Controllers

HC

The simple 6 button "HC" Hand Controller has 6 buttons for:
There is also a RS-232 to TTL level converter so it can be used with the Celestron Star Guide software to make the Tasco Scope into a GoTo scope with the addition of a computer.  The RS-232 connector is a 4 Position 4 Place Modular connector (the stnadard phone line connector is a 4 position 6 place and will not fit).

When a computer is controlling the scope the "HC" hand controller probably just passes through the commands to the motor control PICs.  The PIC in the "HC" hand controller may just generate the 4 directional commands and control the LEDs, or it may have more capability

GT

The Nexstar scopes now sold come with the GoTo hand controller so that an external computer is not needed.  It has a LCD for prompts and a numeric key pad in addition to some special purpose keys.  A copmuter can be connected using the same cable as for the HC hand controller.

Original NexStar 60/80/114/4 GT and Tasco StarGuide - info about bugs in Tasco hand controller.
You can determine if you have the original model by the lack of the two-star and quick alignment options that were added to the new GT hand control.

DC Power

Main Mount

Factory AA batery Pack

8 AA Bat PackThe factory supplied battery pack holds 8 each AA cells.  This provides about 12 Volts for Alkaline cells and about 9.6 Volts for rechargable Ni-Cad or Ni-MH cells.  But the amp hour capacity is only good for a few hours.




10 D Cell Battery Pack

I make a battery adapter that holds 10 each D cells providing 15 Volts for Alkaline or 12 Volts for rechargable cells.  The Power Pole option (257477BA-PP) allows a cable with Power Pole connectors to be connected to the battery pack.  I made up a short Power Pole to 5.52.0 mm connector cable which connects to a Power Pole extension then to the scope.  These scopes are rated for 8 to 18 Volts input so this is well within specs.  (I have a few of the 5.5x2.0 connectors on a short cord if you need one they're for sale)

Finder Scope

Uses a CR2032   3 Volt Button Cell.

Inside

How It Works

Inside N60 ArmThe Az and El axis are rotated by DC gear head motors that have a 45 tooth wheel on the motor shaft.  A photo sensor with In phase and Quaderature outputs feeds back to the microcontroller the incremental change in position (2 degrees at motor shaft, 0.26" at scope or  an overall gear reduction of about 5 million, but the software structure limits the presision to 1/(2^16) or 19.77") and the direction of rotation.  The microcontroller has a Pulse Width Modulation output that is fed through an octal buffer and then on to a dual H-bridge driver that controls the Az and El motors.  The PWM has a 10 bit range so there are 10 possible motor speeds (spec says 4 slew, 4 tracking, and 5 multiples of tracking, so a timer prescaler is being used in addition to the PWM) . The motor controllers get their commands through the modular jack on the mount by means of the motor control protocol at TTL levels.

Main PCBBoth motor control chips are identical, but one has pin 15 tied to ground and the other has pin 15 tied to +5, so they will interpret commands differently.  There are separator characters in the commands to the motor controllers so that they can ignore the commands for the other axis.  When responding to commands there must be a delay in the El response to allow for the Az response to be sent.

The motor control microcontrollers have built in PWM and serial functions and so these do not take up any processor overhead leaving the uC free to do other things, like constantly calculate the new rates.

The board has 4 diodes that may be in a bridge configuration, and if this is connected to the input jack then the scope does not care about polarity or AC vs. DC power (have NOT tested this idea).  The Specifications say 8 to 18 Volts DC with tip Positive

Inside HC Hand CtrlrThe simple "HC" Hand Controller has a microcontroller that reads the buttons, drives the LEDs and sends the button commands to the motor controllers.  It also has a TTL to RS-232 level converter for transmit and receive data from a computer.  Since the level converter does not have any intelligence the protocol at the motor controller is the same for both.  The only new commands are those generated by the buttons on any of the hand controllers.




Ideas

The manual hand controller is the one needed for use with the Celestron Guide Star Software and the associated Arrows software.

Baader Planetarium NexStar Bracket - allows attaching a wide variety of Optical Tube Assemblies or Video cameras

Mintron 12V1-EX low light level CCTV camera can see about 3 to 4 star magnitudes fainter than the human eye.  The Rainbow CCTV lens H20X15M is a three motor (Zoom from 15 to 300 mm,  Focus and Iris ) allowing remote operation.
My Mintron Star Magnitude web site with a lot more about the Mintron and Watec cameras.

A replacement for the existing 60mm refractor may be the Stellarvue - Nighthawk AT1010.
TelevueAstro Physics, Orion - Short Tube 80, 80mm ED Apochromatic, Megrez 80, Borg, and others offer the short tube scopes with objective diameters near 80 mm.

Yahoo Groups

AstroGeeks hc Anywhere - Hand Control Anywhere
Baby Nexstar -
Nexstar -
VideoAstro - Web Page -
Satellitetracker -

Patents

6467738  Tripod-structure for telescopes  October 22, 2002 Celestron Int 248/164; 248/177.1; 248/188.6; 248/188.7; 359/430
D454899  Single fork arm telescope mount March 26, 2002 Celestron Int D16/132

Links

AstroGeeks - hcAnywhere allows a PC to replace the GoTo hand controller.
Ed's NexStar™ 11 GPS Etc., Astronomy Site -
Matthias Bopp, DD1US - Astronomy -
Ray's Brackets - similar idea to the Baader Brackets for this scope, allows better balance or diffferent OTAs to be used on the N5 or N8 scopes
Satellite Tracker by
Brent Boshart
nexstar11.comNexstar revealed - Internal views of a Nexstar 8GPS
Nexstar Resource Site -
NexStar Info: - has NexStar AUX Command Set and others
eBay seller bern-gs10 makes adapters for the Nexstar/Tasco 60 mm scope mounts that allow attaching other scopes, similar in function to the Baader Brackets, but lower in cost.
Brooke's Home Page

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