Design and development of control unit and software for the ADFOSC instrument of the 3.6 m Devasthal optical telescope

ABSTRACT In this paper, we describe the details of control unit and GUI software for positioning two lter wheels, aslit wheel and a grism wheel in the ADFOSC instrument. This is a rst generation instrument being builtfor the 3.6 m Devasthal optical telescope. The control hardware consists of ve electronic boards based onlow cost 8-bit PIC microcontrollers and are distributed over I2C bus. The four wheels are controlled by fouridentical boards which are con gured in I2C slave mode while the fth board acts as an I2C master for sendingcommands to and receiving status from the slave boards. The master also communicates with the interfacingPC over TCP/IP protocol using simple ASCII commands. For moving the wheels stepper motors along withsuitable ampli ers have been employed. Homing after powering ON is achieved using hall e ect sensors. Byimplementing distributed controlunits havingidentical design modularity is achievedenabling easiermaintenanceand upgradation. A GUI based software for commanding the instrument is developed in Microsoft Visual C++.For operatingthe system during observationsthe user selects normalmode while the engineeringmode is availablefor o ering additional exibility and low level control during maintenance and testing. A detailed time-stampedlog of commands, status and errors are continuously generated. Both the control unit and the software havebeen successfully tested and integrated with the ADFOSC instrument.Keywords: 3.6 m telescope, faint object spectrograph, control unit, GUI software, microcontroller, I2C