M.Ing. / This thesis describes a full design project of a processor based sophisticated measurement instrument - the datalogger. It covers the theoretical approach to the design project followed with hardware and software design. Many nonstandard solutions in hardware and software parts are used to approach a target, and they are fully described. The world that surrounds us today is full of products based on science and technology knowledge. These products are part of everyday life. The development of science and technology is very much depend upon a parallel development of measurement techniques and instruments. Measurement and the technology of measurement called instrumentation, serves not only science but all branches of engineering, medicine and almost every sphere of human life. Measuring instruments are used in the monitoring and control of processes and operations, too. Most specialised instruments, such as the datalogger, are used in experimental, research and develop science and engineering work. This thesis is organised into six chapters. The dataloger position in the measurement instruments tree is shown in the first chapter. The electronics design philosophy follows in the next chapter. It covers the most common problems found when the new design project starts. The global design strategy with brief description of all steps follows. The second chapter contains the datalogger project history, the reasons for going into the project, and the requests of the new device, too. At the end of this chapter the basic work principle of the datalogger is described to allow an easily following applied solutions. The third chapter covers all datalogger design specialities that make the datalogger design different from the design of other measurement instruments. It starts with remote sensors problems and problems commonly connected to the input stage of similar systems. The second half of this chapter analyses the instrument precision and error sources. There are several different methods that precision can be increased. Two methods applied here, reducing measurement range and oversampling with noise, are briefly described. The forth chapter interpretates the design of the processor board. It starts with a general microcontroller overview, describing the reasons for selecting the Hitachi microcontroller H8/532. The most important microcontroller characteristics are shown, too. The second part of this chapter contains the organisation, connections and contents of other electronics blocks in the processor board. At the end of this chapter the processor board schematic and full characteristics are given. The datalogger's hardware is described in the fifth chapter. The basic work principles of the various hardware parts are given in the beginning. The hardware is broken down and described in the following way: power electronics, digital control, signal processing part, and interface cards. All parts are covered with detailed descriptions of design circuit and the following calculation. The last chapter shows the software for the datalogger. It starts with the mathematical calculation principle developed and used in the datalogger. The customer part which follows covers software and hardware part relation between user and datalogger. One of the datalogger's software speciality is organisation of RAM space which allows high software flexibility of the datalogger as a measurement instrument. At the end the full datalogger program organisation is given on a global level.