Amateur Telescope making

A Printed Circuit Board (PCB) design for Mel Bartels' Alt/Az drive system

NOTE 1:
This PCB Layout does NOT include the new added feature of field rotation! For a description of my fieldrotation daughterboard go to my Fieldrotation page.
NOTE 2:
Many people asked me to sell them one of my circuit boards. I do NOT manufacture or sell those boards! It is actually quite easy to make them. I however will be happy to answer any question about the process of building one.
NOTE 3:
Neither PCB's manufactured using my design nor the design itself may be sold. The use of the content of this page for any kind of publication needs the agreement of Mel Bartel's and myself.


Also see my CompuDob page that displays my 6" Computerized Dobsonian telescope


Preface

I assume that the reader is familiar with the basic process of etching printed circuit boards. If not, I recommend to look through the reference section at the end of this page.

The reader has to take all necessary safety precautions while handling the chemicals for PCB etching!
Those include: Rubber Gloves, glasses to protect the eyes, apron, suitable and well-ventilated working area.


Materials needed

You can also expose the artwork on the board. In that case you will need a photosensitized copper board and all the chemicals to develop the board.


Layout

Download the 120k ZIP file with the Postscript/Acrobat files and unpack it to a directory on your hard disk.

The archive contains the following files:

ARTWORK.PS / ARTWORK.PDF
is the unmirrored Artwork files in postscript/Acrobat format

MIR-ART.PS / MIR-ART.PDF
is the mirrored Artwork files in postscript/Acrobat format

SILK.PS / SILK.PDF
is the unmirrored Silkscreen files in postscript/Acrobat format

MIR-SILK.PS / MIR-SILK.PDF
is the mirrored Silkscreen files in postscript/Acrobat format

ALTAZ.JOB
is the JOB file for the PADS-PCB program. If you have PADS-PCB you can edit the Artwork.
Important:
If you are using Toner transfer paper then you must use: ARTWORK.PS or ARTWORK.PDF and MIR-SILK.PS or MIR-SILK.PDF
If you want to expose the artwork on photosensitized board then you must use: MIR-ART.PS or MIR-ART.PDF and SILK.PS or SILK.PDF
To view or print these files, you will need: Acrobate reader or Ghostscript , which view and print postscript files on any computer or printer.

Images

Artwork The artwork unmirrored
(for the PCB, only use the supplied high resolution .PS Postscript file. This one is a low resolution .GIF file)
(Click on the small icon to see larger image)
  • The artwork includes a large surface-area groundplane for better circuit stability. The ground traces across the board are broader for the same reason.
  • Above the transistor pads are the big 3mm mounting holes for the heatsinks. There is enough space on the board to mount the transistors/voltage-regulator + TO220 heatsinks horizontally.
  • For offboard connections I used single row straight PCB plugs.
Silkscreen The silkscreen unmirrored
(for the PCB, only use the supplied high resolution .PS Postscript file. This one is a low resolution .GIF file)
(Click on the small icon to see larger image)
  • The black lines are jumper wires.
  • PP2,PP3 etc. stands for connections to the referring pin of the parallel Port
  • M1 is the output to the Altitude Motor. M2 is the output to the Azimuth Motor.
  • The long 8-pin connector is the out/input to/from the handpad.
  • +12V and GND are the pins for offboard voltage and ground connections, like the 12V connection to the stepper motors and the ground connection to the parallel port.
  • On some diode symbols, the line to mark the cathode is missing. However the square pad marks the cathode.
Schematic The schematic
(Click on the small icon to see larger image)
  • Pin 7 and 14 of the Hex inverter are of course connected to Ground (pin7) and +5V (pin14). They don't appear on the circuit because the PCB software handles all Ground/Power connections by itself.
  • The color coding for the handpad cable is my invention. You can of corse use whatever colors you want for the handpad wires.
The following photographs show the ready assembled PCB board.
PCB bottom side (photograph) The bottom side gives a little impression about the quality of etching that can be achieved by using Iron-on-Foil.
(Click on the small icon to see larger image)
PCB top side with components (photograph) The top side shows the spacing of the assembled components.
(Click on the small icon to see larger image)
The next two photographs show my version of the handpad.
(Click on the small icon to see larger image)
Handpad topview
Handpad wiring
I used a momentary On-Off-On switch for the Init-button .
This is a picture of my electronic-box design.
(Click on the small icon to see larger image)
Electronic box Using the single row PCB-plugs for the offboard connections you can provide for clean wiring and avoid mistakes.

Reference

Reading:
How to computerize a Dobsonian Telescope by Mel Bartels
Making Printed Circuit Boards by Jan Axelson. ISBN 0-8306-3951-9
Electronic prototyping: Tips and Pitfalls
Iron-on toner transfer papers:
DynaArt's toner transfer paper
Press-n-Peel film
TEC-200 film
Surplus electronic components:
Greenweld
Software:
Electronic design/CAD software

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© 1996 Contact Berthold Hamburger