M. Amer Iqbal Qureshi
part based upon microcontroller, which we will be working
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part based upon microcontroller, which we will be working on in this project, and a suitable input part which captures the real world event, and converts it into appropriate mi- crocontroller readable pulse. For example if you want to measure the radio-frequency you need a suitable adapter, that will capture the radio signal, and convert it into digital signal. Since frequency of any event is usually variable, it is mandatory to sample the events frequently and update the display continuously. From this perspective there are two types of frequency counters, one which take the sample when required and display the result, they do not take another sample unless told to do so. The other type will continuously take samples of the input line and update the display. The time duration after which samples will be taken dictate the resolution of counter. Real time counters, do it almost continuously. A simple frequency counter measures frequency by counting the number of edges of an input signal over a defined period of time (T). A more complex method is reciprocal counting (we shall talk about it later). Frequency is defined as (Number of events) / (time in seconds) and measured in Hz. To make calculations trivial using a 1 second gate time (T) gives a direct reading of frequency from the edge counter. Making a frequency counter for frequencies up to 65.535kHz is easy as the counters in a PIC chip can count up to 65535 without overflowing. Up to 65.535kHz all you do is wait for 1 second while the count accumu- lates, read the value and display it. It will be the frequency in Hertz. Above 65.536kHz you have to monitor the overflow value while at the same time making an accurate delay time (T). Note: Using a 1 second measurement period results in the frequency counter count value being a direct measurement of frequency requiring no further processing. It also means that the measurement is resolved to 1Hz. (Increasing T to 10s resolves to 0.1Hz while using T=0.1s gives a resolution of 10Hz). tải về 3.06 Mb. Chia sẻ với bạn bè của bạn:
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