frequency counter

The frequency counter is the most popular instrument in the home maid instruments. I think that the reason why it is built widely is: it can be built easily because it is digital circuit, it is generic measurement and many construction kits are available. Many electronics hobbyists will experienced to build any frequency counter. This project is second trial for me. But building two ordinaly frequency counter is not smart so that some additional functions ware impremented to the frequency counter. The function is not that abundant compared to generic universal counter however it can measure pulse period/width besides frequency, I named this project `Universal Counter`.
frequency counter  - schematic

The Frequency means number of electrical or mechanical vibration cycles per unit time, to explain this might not be needed now... Hz (hertz) is used for a unit of the frequency and is defined as an SI unit, and it means number of cycles per second: e.g. when 100 cycles are counted per a second, it is 100 Hz. Formarly c/s was used for unit of the frequency. When count number of cycles of the input signal for one second, the value of frequency can be got in the counter. This can be realized by simple counter circuit so that this was the conventional frequency measureing method. Many counter IC have been released and many frequency counters thak work in this method are being shipped now. An AT90S8515 is used for the controller because it is very easy to use. The control process are conting, displaying and communicating mainly. They are not that complex, any other microcontroller, such as 8051, H8 and 78K, will able to be used instead. This is the simplest method but the measureing resolution is limited at low frequency. To ensure more resolution, the gate time must be expanded: e.g. when measure at resolution of 1 mHz, 1000 seconds is needed to measure one time. Every measureing method needs to control any clock signal. However using an AND gate that shown in the diagram of principle will occure an extra count. The error rate depands on the duty ratio of the clock signal: e.g. simmetrical clock signal occures +0.5 counts...

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