AF counter circuits

Posted on Feb 6, 2014

A digital AF (audio frequency) counter can be constructed with only few components by using a single 7226B IC from Intensil as shown in the diagram. The upper frequency limit of this circuit is 9 MHz. The four important functions in the frequency counter are: pulse processing, multipying, counting with timebase, and display. The input signal is co

AF counter circuits
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nverted to a squarewave pulse by the input circuitry. The input circuitry is protected up to 50 Vrms. Its impedance is around 2 megaohms. The signal is then multiplied by a factor of 100. The counting process is done by the IC 7226B. This IC integrates the following circuits: oscillator with timebase; gating circuitry; counter stages; and a 7-segment display driver with multiplexer. Switch S1 enables one to choose between the original frequency or the one multiplied by 100. Multiplying the input by 100 enables the frequency range 5 Hz to 5 kHz to be displayed. S2 selects the measuring range while S3 is the power supply switch.

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