Computer interfaced CCD camera

Abstract

This thesis work is aimed at the building of a computerinterfaced CCD (Charge Coupled Device) camera; which will bepart of a fluorescence ratio imaging system, measuringcytosolic free Ca++ concentration. As in the current systems,for ratio imaging of rapidly responding cells, theincompatibility with the standard video is a serious problemthe analog video output is directly digitised using a flashADC (Analog to Digital Converter); and 7-bit digital data istransferred to the computer memory using DMA (Direct MemoryAccess). So, the data acquisition rate is only limited by theCCD and the computer performance.The system is designed around an IBM compatible PC/AT.Electronic hardware is composed of fourcard connected to PC via the expansioncards: an adapterslots, a voltageregulator , an ADC and a CCD card. The mechanical hardware issimply a light isolated housing carrying the last threecards. It is coupled to a student microscope with removedoculaire to give a real image on the CCD surface. The chargepackages are collected at the potential wells of CCD whichare clocked out by supplying the gating pulses. The gatingpulses together with the DMA control signals are generated atthe adapter card.The software initiates the data acquisition process.When a word (two bytes) of data is ready, the PAL(Programmable Logic Array) produces a DRQ (DMA Request)signal. When the data is transferred to memory PC sends aDACK (DMA Acknowledge) signal. PAL holds the clocking out ofthe CCD until DACK comes. Once all of the pixels are clockedout, PC sends a TC (Termination Count) signal which in turngenerates a hardware interrupt. Once this interrupt isrecognised by PC: a new data acquisition sequence will start;but this time on a second buffer leaving the first bufferavailable for any real time data processing; thereby creatinga kind of background task. The limiting frame rate of thecamera is 100 Hz; while with the 18 MHz PC resulting imagesare obtained at 33 Hz.The processed images are 64 gray level black-and-whiteor pseudocolored images. Black-and-white images were used tofocus on the target cells. pseudocolored ones will be used torelate the light intensity to a local analyte concentration.