Frequency Counter

In this project we are building a basic and low cost frequency counter circuit . It can measure from 16Hz to 100Hz signals with a maximum amplitude of 15V. The sensitivity is high, the resolution is 0.01 Hz. The input signal can be a sine, a square or a triangle waveform.

The counter can be used in many applications. For instance, to observe an oscillator’s accuracy, to measure the mains frequency or to find out the rpm of a motor that is connected to an encoder.

The CCP (Capture/Compare/PWM) module of the PIC microcontroller counts the input signal. Only the capture function is used. To learn more about the CCP module of the PIC please visit www.microchip.com.

Before measuring the frequency of the input signal, the signal must be converted to the square waveform. So an optical isolator circuitry with 4N25 optocoupler is used for this purpose. So the input signal is safely isolated from the microcontroller circuit and converted to square wave. The signal amplitude must not exceed 15V. If this happens, 1k resistor may burn. If you want to measure the mains frequency, you should use a 220V/9V transformer first.

Frequency Meter for 10 Hz to 100 kHz Input by 74121

Description:

This frequency meter is suitable for sinusoidal wave and square wave input signals. Minimum input potential must be 25mV(rms). Measurement range can be determined from 10 Hz to 100 kHz by using the S1 switch. Each switch position part is calibrated by using 20 kOhm potentiometer. Total current consumption of the circuit is about 10mA. R1 and C1 values should be chosen depending on wheather microampermeter or milliampermeter is used.