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 converted 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.
The counter can be reset through S4 while S5 tests the LED display.
Parts Placement Layout
Electronic Circuits volume 1.0 - Circuit Nr. 66
The complete data of the electronic circuit described above can be found in the following book and is available from Amazon.com.
Click on the image to view the book.