# Cheap frequency meter circuit using 555 and CA3140

The electronics are still used to use a frequency generator circuit beuause It is important. And are used a lot in electronic circuits, both sine, square wave and more. In every time related to the frequency. What that we want to know is how much frequency.
For laboratory common standards. We have many tools available to measure frequency. for example, the Oscilloscope and The Digital frequency counter) But those tools. Usually too expensive. For small laboratories. We Usually want to know how often only approximate.

Learn: How does NE555 timer circuit work

This cheap frequency meter circuit that we show to you. Suitable for general use in small laboratories. Because cheap, easy to build. And Qualified enough. For applications most of the electronics amateur. It can be shown that the frequency read directly from the meter. Can measure the frequency of 100 Hz (full scale) to 100KHz (full scale). By the characteristics of the waves do not affect the accuracy of the circuit. Even low levels, can be measured to a hundred millivolts. (100mV)

The working principle
The working principle of the cheap frequency meter is simple. Internal its there is a generates narrow pulses circuit up. By same frequency as the signal to be measured. These pulses will go to make a meter needle swing more or less. By an average of caused by current pulses.
Which the average value will be ratio with amount of pulses that occur in a time period. The signal that is measured has a low frequency and amount of pulse will be few. The current average flow meter is less. But if the signal that is measure has high frequency, number of pulse too much will has the high average current makes the meter needle swing up.

So, We can set the width of each pulse constant, then The swing of the meter needle is in proportion to the frequency of signal that is measured there. We so adjust the scale of meter to read value as frequency It directly with a linear scale. (each channel of the scale are spaced evenly.)
For A prototype used analog DC meter (or galvanometer
) of 100uA (Full scale) Read convenient frequency. Because there is made a full-scale range, 4 ranges are 100Hz, 1KHz, 10 KHz and 100KHz.

How the circuit works
-In figure 1 is the complete circuit of the cheap frequency meter. This circuit uses two ICs are CA3130 and LM555. The first is a OP-amp Ic is work faster and has the input impedance is very high. This IC is connected as the schmitt trigger circuit to extend the input signal to act up and force you to convert the input signal to a square wave with a fixed height. For the second IC as a timer IC NE555 which is connected as a monostable multivibrator circuit. It will be provides pulse width at the output every time, when has a input complete 1 wave.This pulse will be entered to drive a Moving Coil Type Meter The meter needle indicates an average voltage value of pulse. Which the needle is pointing more or less in proportion to the frequency of input signal.

-When you know the principle roughly, to view the detail of the works. The input signal will be entered to IC1 by through the capacitor C1 to block a DC current that might be coming campsites. They R1,D1 and D2 will act limit size of the input signal is not too higher than voltage drop across diode. While is directed bias to not high until damage to the IC1,R6 and R5 act feed back a positive mode, To create a hysteresis in the area around the level zero voltage of the input signal. Having the hysteresis allows the circuit to be less interference from the noise signal.

-Sine this circuit uses a single power supply source to convenience, so must connect the R2 and R3 to bias to the input pin of IC1 is about half of the power supply. The output from pin 6 of IC1 will be the square wave. Which has frequency equal to the input signal. The square wave signal will be differentiated onto as narrow pulse like a needle shape with C3, R7 and R8. The value of these is assigned to a needle pulse width less than pulse that IC2 will be created. To ensure that IC2 can function correctly, and high reliability.

-This needle Pulse act as signal that enter into trigger to the monostable multivibrator circuit works. The width of pulse that out to pin 3 of IC2 depends on value of C4 and resistors R9-R12 Which the is used to define the frequency range to be measured. Frequency range, these measurements will be provides duty cycle about 75% at frequency 100Hz, 1KHz, 10KHz and 100KHz (select by S1).
-The pulse that out from the IC2 will be be trimmed to size constant at 5.6V. By using the zener diode 5.6V D3 to read all time accurately. The voltage of the battery will decrease.
Note: You can use the input 2 channel “High” or “low” as voltage input and this circuit is desogned for low frequency of 10HZ to high is 100KHz.