FM transmitters and receivers are among the most popular projects for electronics enthusiasts. In this article/video, I will present a detailed design for a digital FM receiver that features an LCD display and three push-buttons. The receiver can scan for FM signals across the 76MHz to 108MHz range both manually and automatically (in Scan mode). The signal strength is visually represented as a bar graph on the LCD screen. The audio output is powered by a 3W+3W Class-D stereo amplifier, delivering high-quality sound with sufficient power. The system is controlled using an affordable and widely used Arduino Nano board. Let’s dive in!
A. Circuit Overview
Figure 1 illustrates the schematic diagram of the digital FM receiver. The circuit consists of three main sections: the Arduino Nano (controller), the FM receiver module, and the audio amplifier.
Figure 1: Schematic diagram of the digital FM receiver
A-1. FM Receiver Module
The FM receiver module uses the well-known TEA5767 chip, which operates via the I2C interface and covers the FM frequency range from 76MHz to 108MHz. It outputs left (L) and right (R) stereo audio signals, which require amplification due to their weak signal strength. The frequency tuning and signal strength detection are handled by the Arduino Nano using custom code.
The components R3, C7, C8, and C9 form a low-pass RC filter that helps reduce power supply noise. Resistors R1 and R2 are pull-up resistors necessary for the I2C communication, and CON1 is a UFL connector for the antenna. Figure 2 shows the TEA5767 module.
Figure 2: The TEA5767 FM receiver module
A-2. Audio Amplifier
The audio amplifier is based on the PAM8403 chip, a 3W+3W HiFi Class-D amplifier. It operates efficiently from a single 5V power supply and is capable of driving 4-ohm speakers to their maximum output. The PAM8403 is known for its low Total Harmonic Distortion (THD) and Noise (THD+N), which ensures high-quality sound reproduction. Its filterless architecture allows direct speaker connection, eliminating the need for output filters, saving both cost and PCB space.
Components C13, C14, and C15 are bypass capacitors that reduce supply noise. R4, R5, C11, and C12 are part of the audio signal routing to the amplifier. Figure 3 shows the reference circuit for the PAM8403 chip. P2 and P3 are 2-pin right-angle connectors used to connect the speakers to the PCB.
Figure 3: PAM8403 datasheet reference circuit
A-3. Controller
The controller for the system is the Arduino Nano (AR1). Figure 4 shows the Arduino Nano board. This board interfaces with an 8×2 LCD (LCD1) to display the frequency and signal strength, while also reading the states of the SW1, SW2, and SW3 push-buttons. It communicates with the TEA5767 chip over the I2C bus. Resistor R6 adjusts the LCD contrast, while capacitors C4, C5, and C6 debounce the mechanical push-buttons to prevent erratic behavior.
Figure 4: The Arduino Nano board
A-4. Power Supply
The TS2937 chip is responsible for supplying a stable 5V voltage to the entire circuit. Capacitors C1, C2, and C3 filter out noise, while POT1 is a 50K dual potentiometer with a switch that controls both the device’s power and the audio volume. Figure 5 shows an image of the POT1 component.
Figure 5: 2-Way (Dual) potentiometer with switch
B. PCB Layout
Figure 6 presents the PCB layout of the digital FM receiver. The board is a 2-layer design, with the Arduino Nano mounted on the bottom side and the LCD placed on the top side, typically using female pin headers for easy attachment. This configuration is more clearly shown in the 3D views and photographs. Figure 7 provides a 3D view of the board, while Figure 8 shows the high-quality fabricated PCB of the digital FM receiver.
Figure 6: PCB layout of the digital FM receiver
Figure 7: Top and bottom 3D views of the PCB board
Figure 8: High-quality fabricated PCB boards
The PCB components for IC1 and IC2 were sourced from the SamacSys component libraries, which streamline the design process, minimize errors, and lower product costs. These libraries are free to use and comply with industrial IPC footprint standards. They can be downloaded or accessed via CAD plugins from componentsearchengine.com. SamacSys supports most major CAD tools, including Altium, Eagle, KiCad, OrCAD, and Proteus, as shown in Figure 9. Figure 10 demonstrates the selected component libraries from the Altium plugin.
