| Abstract : | The GROWTH India telescope (GIT), India’s first robotic telescope, is equipped with SDSS filters u’ g’ r’ i’ z’. The filters are housed in a filterwheel and need to be rotated and positioned precisely before the detector/camera. The closed-loop control system provides precise position and velocity control of the filter wheel and is realized with a system-on-chip (SoC) architecture based PSoC5LP microcontroller unit (MCU). The system is designed keeping in view that the telescope operation is robotic. A command set based on RS232 protocol is developed for communication with the host computer. The commands are provided from a python script which is integrated with the main observing script. Distinct from the previous system, the controller exploits a shortest path algorithm, velocity profile, and an interrupt system to ensure high precision control and homing accuracy. The on-chip Quadrature Encoder Interface (QEI) module is utilized to interface the encoder position feedback mechanism. The Direct Digital Synthesis (DDS) module provides digital output in a wide frequency range with the 24-bit resolution required for a stepper motor drive system. The control components comprise PSoC5LP MCU, MAX3232 chip for RS232 communication to PC, index sensor, incremental encoder, stepper motor, and drive.
+/- 3 encoder counts or < 1 arcminute of positioning accuracy is achieved and the system is operational with the telescope since May 2021. |
