Voltmeter designing based on microprocessor Abstract: In modern measuring technology, it is often required to conduct site measuring with a digital voltmeter. The data measured will then be input into the micro-computer system to execute such functions like calculating, storing, controlling and displaying. The digital voltmeter control system described in this paper makes use of AT89c51 SC computer and ADC0804 A/D converter to fulfill the designing of the software as well as the electrical circuit. The voltmeter features in simple electrical circuit, lower use of elements, low cost and automatic regulation, while it can also easily carry out the duties of measuring remote transfer of measuring data. The meter is capable of measuring voltage inputs ranging from 0 to 51 volt, and displaying the measurements in turn or only that from a selected route. Key words: SC computer; digital voltmeter; A/D conversion; analogue signal