Electronics and Software

The electronics of LonGSp is composed of two main parts: "upper" electronics, that is situated near the instrument, and the "lower" electronics, put in the control room. The connection between the two parts of electronics is assured via a fiber-optics link.

Two boards, close to the cryostat, carry part of the interface electronics, that is a set of four preamplifiers and level shifters and an array of drivers and filters that feed the clock signals and the bias to the array multiplexer. There is also the main electronics box that contains the amplifiers and the A/D converters for the four output signals from the detector, the sequence memory which generates the proper timing clocks, and a logic for converting the 16-bit parallel data from the array to a serial format. A transceiver sends data to the control room through a fiber optics link. A 65C02 microprocessor supervises and synchronizes the different tasks. The fiber optics link is bidirectional, so that it is possible to send instructions to the control microprocessor in the "upper" electronics, and to communicate with motors control through a serial connection (RS-232) encoded on the same fiber-optics link. The "upper" electronics is completed by the box which contains the power supply, the stepper motors control and the temperature controller of the array.

The "lower" electronics implements the logic to decode the serial data protocol, to correctly reconstruct the frame coming from the array detector. The instrument is controlled by an MS-DOS PC equipped with a 80486 CPU (33 MHz clock), high-resolution monitor, and a 220 Mb hard disk. The 16-bit parallel data from the electronics are presented to a custom interface board (named Ping-Pong) inside the control PC which stores one or more full frames in a buffer memory before sending them to the memory of the PC. At the end of a data acquisition sequence, each single frame or the stack average of a group of frames is stored on disk. The hard disk is used only to store the data temporarily, the data are archived permanently by CD writer, also connected to the control computer.

Data are stored in the form of 16-bits FITS files, with the relevant information of acquisition (e.g., observer name, object name, observatory, date, time, detector parameters, telescope position, filter, wavelength, ecc.) written to the header of the files. A local Ethernet network connects the control computer to the Sun Workstation of the TIRGO, so that it is possible to transfer the data for preliminary reduction using standard package.

Particularly the form of fits file is completely compatible with the context IRSPEC of the ESO package MIDAS: data reduction can so carry out using this facility.

Last update 10 May 96

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