Alcor - A Microcontroller-Based Control Circuit
for Conventional AC Telescope Drives

Michael A. Covington
Institute for Artificial Intelligence
The University of Georgia
Covington Innovations
Athens, Georgia

Many telescopes still use 50- or 60-Hz AC motors controlled by variable-frequency AC power sources. This paper describes a programmed microcontroller that can be used as the oscillating element in such drive controllers, providing efficient two-phase drive, smooth frequency changes, and precise sidereal and lunar rates.

Click here to read the paper
More downloads are below.

NOTE ADDED 2019: This project is over 20 years old, and the microcontroller needed for it may be hard to get. Use the PIC16F84A chip, which is still in production. It can be programmed with the current PICkit 2, PICkit 3, and other ICSP (in-circuit serial programming) programmers that are capable of high-voltage programming. To find out how, click here.

The .HEX files have been zipped because some browsers would not download the original versions properly.

As recently as 2019 I have added a new version, 1.260, for drives that give sidereal rate on 60 or 50 Hz, such as Byers drives with special gears.

Please note that the published paper is a reference design intended to inspire other designs, not "plans" to be built by people who do not understand the circuit. If you do not understand the circuit and are not equipped to troubleshoot it, please get help locally from someone more experienced. Many ALCORs have been built and used successfully, but this is not a commercial product and is not supported by anyone.

If you cannot program PICs yourself, ask for help locally and on the Internet. Chips can be programmed by vendors (Digi-Key, or Microchip themselves), but the setup cost is high ($60-$100). It is cheaper to buy your own programmer, such as a secondhand PICkit 3.

NOTE ADDED 2005: The PIC16F84 and PIC16F84A are not interchangeable. The assembly-language program must be assembled for the right one. Be sure you download the version that corresponds to the processor you are using.

The PIC16LF84A is a complete substitute for the PIC16F84A and is what I am now using for new Alcor circuits. It uses the same .ASM and .HEX files.

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