PIC Based Position Controller

Introduction

This controller hardware is the interface between the PC based high-level control and the variable frequency (VF) drives that run the Az

Prototype PIC based position controller used to interface Paratrack to the dish steering motors.

and El motors. The PC is running a program called Paratrak that was written by students at CU as a senior project. Paratrak provides a user interface and the complex calculation necessary to usefully position the dish. The controller accepts a simple command stream via a serial interface from the PC that describes where the dish should be pointing. The controller does not know about angles in terms of degrees minutes and seconds, but in terms of a "count" that it calculates from encoders on the Az and El gears of the dish.

Since PCs (and Windows) can sometimes crash, protection is built in to the controller so it will not do damage to the dish should the PC program malfunction. It has limits built in to prevent movement of the dish beyond 90.5 degrees up or -0.5 degrees down. This prevents the dish from running into mechanical stops. It also stops all movement if it does not receive any communication from the PC for 5 seconds and stows the dish (points it straight up) if it does not hear from the computer for 2 minutes.

The controller is built around two Microchip PIC microcontrollers, one to control Az and one to control El position. It also includes relays and amplifiers to command the VF drives to move the motors in one direction or the other and control their speed.

Controller Schematics:

Controller Block Diagram

Azimuth Controller

Azimuth Speed Isolation Amplifier

Elevation Controller

Elevation Speed Isolation Amplifier

Speed Signal Amplifiers

Relays