Altitude-Azimuth Controller




Below are some images of a Alt/Az controller I made for computer controlled tracking of my telescope. The controller was designed by Mel Bartel's. He created the software and the original circuit. That circuit has been replaced with a new circuit design that has a doubled sided printed circuit board available from him separately or in kit form. Follow the link below to Mel's site where all pertinent info. on the controller can be found. The other board in the controller enclosure is the current limit circuit contributed by Jean-Charles Vachon.

Mel Bartel's Web Site

Click on an image to enlarge...Back to return.

Since I built the first controller I have built two more with some minor changes. I have added a rotary switch to the meter so one can switch between reading current and voltage. I removed the current limit control board since I am now using twelve volt stepper motors. This has been replaced with a board that holds the DC/DC converter and four voltage limiting resistors. These resistors keep the voltage across the field derotator motor at the 9.2 volts specified for my particular bipolar stepper motor. This is to keep the current limits required with in the motors current requirements but not drawing any more than required as would be the case running the motor straight from a twelve volt source. The MC7439 runs hot enough, as it is, with out carrying the burden of dissipating unneeded excess power as heat.

I made a change in the connector for the limit switches due to a lack of ready availability for the bayonet style connector used on the first controller. I added a reversed biased diode across the twelve volt input connector in case of an accidental reversal of the battery connections. This is conjunction with a fuse in the connecting power cord should prevent any major disasters.
Below are some images of the changes made.


The next row of images has a picture of my test set up. The next two are rear and side views with the cables connected. The last two are images of the flexible shaft couplers I obtained from Jameco Electronics. I used 13/16 dia. heat shrink tubbing to keep them together while allowing the parts full freedom of movement.




To the right are images of the layouts for the two printed circuit boards I made.
The left image is of the paddle's printed circuit board layout and the middle image is a layout for the motor current limit board. The far right image is for the DCDC converter and the current limiting resistors for the field derotator stepper motor coils.

The next two images are of the paddle board with components in place and mounted in the plastic enclosure.
The second image with different colored buttons is a later version in case anyone is wondering. The enclosure is very small. 2.5"L x 1.6"W x .865"H

I had some difficulty following the paddle controller wiring from the paddle buttons to the MJ-11 connector, the connectors pin orientation in relation to the six wire cable, and the DB25 connector pins 10 through 13. I also found the diagrams for the paddle a little vague. I was able to figure it out with some study but I could easily imagine that someone not well versed in electronics or schematic reading would become hopelessly confused. Therefore I have drawn a schematic of the connections between the paddle's components, the cable connections to those components, and the connectors on the main controller board. I hope they will help divert some future grief. The other link is a schematic diagram for the connections between components in the enclosure.


Paddle Interface Schematic
Enclosure Wiring Schematic


Click on links below to see other individuals controller projects and related sites.
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LINKS
Chuck Shaw's Alt/Az Comments
Berthold Hamburger's Computerized 6 inch DOB.
Make your own Digital Setting Circles
David Rowe's dual axis controller
Stepper Motor control by Computer
Jeff DeTray's stepper motor barn door mount
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