Digital Frequency Meter Using Arduino


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This article describes the implementation of a digital frequency meter using Arduino Uno to determine the sinusoidal frequency signal in the range of 20Hz to 5kHz. The logic involves counting the total number of pulses per second that appear at a digital pin of Arduino.

The authors’ prototype is shown in Fig. 1.

Authors’ prototype of digital frequency meter
Fig. 1: Authors’ prototype of digital frequency meter

Block diagram of the digital frequency meter is shown in Fig. 2.

 Block diagram of digital frequency meter
Fig. 2: Block diagram of digital frequency meter

Circuit and working

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The circuit diagram of the digital frequency meter is shown in Fig. 3. It consists of Arduino Uno board, optocoupler MCT2E (IC1), 16×2 LCD and a few other components. The sinusoidal signal whose frequency is to be measured is applied to signal input terminals (CON1), as shown in Fig. 3. In this frequency meter, the test signal must be an alternating one and its amplitude must not exceed the maximum forward diode current rating of the optocoupler for a particular value of series resistance. (Here, we used 1k series resistance.)

Circuit diagram of digital frequency meter
Fig. 3: Circuit diagram of digital frequency meter

The next stage is a bridge rectifier, which converts the alternating signal to fully-rectified pulsating DC signal. This fully-rectified pulsating DC signal is applied to the diode side of the optocoupler. With the help of the optocoupler, spikes are produced. Frequency of the spikes is twice that of test signal input. These spikes are applied to digital I/O pin 5 of Arduino, and the program running in the CPU of the microcontroller (MCU) calculates the frequency of the test signal and displays it on the 16×2 LCD and on the serial monitor of the PC.

Major components used in this project are:

Arduino Uno

Arduino Uno is an AVR ATmega328P MCU-based development board with six analogue input pins and 14 digital I/O pins. The MCU has 32kB ISP flash memory, 2kB RAM and 1kB EEPROM. The board provides the capability of serial communication via UART, SPI and I2C. The MCU can operate at a clock frequency of 16MHz. In this project, digital I/O pin 5 has been used as pulse input pin, and digital I/O pins 7, 8, 9, 10, 11 and 12 of Arduino Uno board are used to interface with the LCD.

Bridge rectifier

The bridge rectifier (BR1) is used to rectify the alternating input signal to pulsating DC.


The optocoupler is used to produce spikes from the pulsating DC waveform.

16×2 LCD

The 16×2 LCD is used to display the frequency. It consists of 16 columns and two rows for displaying data. The LCD used here is a backlit one. It is interfaced with Arduino in 4-bit mode. LCD pins RS, EN, D4, D5, D6 and D7 are connected to digital I/O pins 12, 11, 7, 8, 9 and 10 of Arduino, respectively.


Arduino IDE is used for programming Arduino Uno. Open the source code/sketch (Freq_meter_1.ino), and select the COM port and board from Tools menu in Arduino IDE. After selecting the correct COM port and board, upload the source code to the board.

Download source folder here: click here

Construction and testing

The PCB layout of the digital frequency meter is shown in Fig. 4 and its components layout in Fig. 5.

Actual-size PCB layout of digital frequency meter
Fig. 4: Actual-size PCB layout of digital frequency meter
Components layout for the PCB
Fig. 5: Components layout for the PCB

Download PCB and Component Layout PDFs: click here

Assemble the components on the PCB, as per the circuit diagram. After this, connect the USB cable to Arduino and give the test signal at CON1 and check the frequency on LCD1 and the serial monitor of Arduino.

Shibendu Mahata is M.Tech (gold medallist) in instrumentation and electronics engineering from Jadavpur University. He is interested in designing MCU-based real-time embedded signal processing and process control systems.

Saikat Patra is passionate about electronics and MCU-based embedded system applications.




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