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

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.

NOTE ADDED 2011: This project is over 10 years old and the microcontroller needed for it may be hard to get.

Use the PIC16LF84A chip and the '84A versions of the .HEX files.

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

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. Vendors that sell chips are often able, for a fee, to program them. Dontronics no longer does this, but you may be able to find others that do, or buy your own programmer.

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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