Digital frequency counter

Posted on Feb 7, 2014

The frequency counter has to count the number of cycles per second of an incoming signal. Hence we need a device to count. In electronics circuits, counter ICs are available for counting. These IC`s can count the input pulses. The count is given as coded output from the IC (in binary form or BCD form). The count must be converted into decimal digi

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t to be understood by human beings. More number of IC`s can be cascaded to increase the number of digits. The number of digits required for the counter to display the count value depends on the application and the accuracy needed. In our design we use a single 4 bit BCD high-speed CMOS counter chips. One chip is used for one digits and we use 7 similar ICs to get seven digit counter. Also we use CMOS decoder IC to decode the BCD out put of the counter to drive 7 segment displays. Since the counter can count only digital pulses, we need to convert the incoming signal wave to digital pulse or we should obtain one pulse for every input wave. Hence we need a special circuit to shape the input wave into a square wave of same frequency and amplitude confined to the TTL signal levels. A signal conditioning section is needed for this purpose. Besides the above initial stages, some times a few more additional stages such as input protection stages, filter stages, etc are can be found in some designs. The input whose frequency is to measured is given to the input stage consisting of the above and the out put of this stage is the square pulses. Now the square pulses are given to the counter to count the number of pulses for a fixed duration. If the duration is 1 seconds, then the counter displays a value that equals to the number of cycles per second, now if we want to measure a frequency of say 20MHz, the counter should display...

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