In this article, a complete digital FM receiver design is introduced, which is equipped with an LCD screen and three buttons. It can manually and automatically search (scan mode) from 76MHz to 108MHz FM signals. The signal strength is also displayed on the LCD screen with a bar chart. The output of the output is amplified by a 3W + 3W D Class Di-stereo amplifier, and the amplifier processes high quality and sufficient audio power. For the controller, the affordable and popular Arduino-NANO development board is selected.
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First, circuit analysis
The circuit diagram is a schematic diagram of a digital FM receiver, including 3 main portions: Arduino-nano (controller), FM receiver module, and audio amplifier. Be
1, FM receiver module
The FM receiver module is based on the TEA5767 [1, 2] chip. It can be controlled by the I2C bus. Covered the FM frequency range from 76 MHz to 108MHz. At the output, it handles the L and R stereo audio signals that should be enlarged. Otherwise, the sound level is weak, even if the headset can be heard. The frequency selection and signal strength measurement tasks are executed by the Arduino-NANO code. Be
R3, C7, C8 and C9 construct a first-order low-pass RC filter that reduces power supply noise. R1 and R2 are the forced pull-up resistor of the I2C bus, and CON1 is a UFL connector that provides an antenna connection.
(TEA5767 module)
2, audio amplifier
The audio amplifier portion consists of a PAM8403 [3, 4] chip. The chip is a 3W + 3W HIFI D amplifier that can only work with a single power supply. Using 4 ohm speakers can reach maximum output power. According to the data table: The PAM8403 is a 3W D audio amplifier. It has lower THD + N to achieve high quality sound reproduction. The new non-filter architecture allows the device to drive the speaker directly and does not require low-pass output filters, thereby saving system cost and PCB area.
C13, C14 and C15 are bypass capacitors for reducing power supply noise. R4, R5, C11 and C12 are used to transmit output audio to amplifiers. P2 and P3 are right angles 2-pin XH connector for connecting speakers to boards. Be
(Reference circuit of PAM8403 chip)
3, controller
The controller of the circuit consists of Arduino-nano board (AR1). Evaluation Board Driver 8 * 2 LCD (LCD1) and read the status of the SW1, SW2, and SW3 buttons. It also transmits / receives TEA5767 data via the I2C bus. R6 sets the contrast, C4, C5, and C6 for reducing the noise of the mechanical buttons (reverse jump).
(Arduino-nano board)
4, power supply
TS2937 [5, 6] is the main component of the power supply, which provides a stable + 5V power supply for the circuit. C1, C2 and C3 are used to reduce noise, and POT1 is a 50k 2 (dual) potentiometer with a switch. POT1 can be opened / closed, or the sound level can be increased or reduced.
(Picture of Pot1)
Second, PCB layout
The PCB of the digital FM receiver is a 2-layer PCB board (latest version). The Arduino-nano board is mounted at the bottom of the board, and the LCD is installed on the top of the board, preferably installed on the busbar. This is more clear in 3D views and real photos.
(Digital FM receiver PCB layout)
(3D view of board)
(High quality prefabricated PCB board for digital FM receiver circuit)
Third, CAD
The SAMACSYS component library (for IC1 and IC2) is used in this PCB project. This saves a lot of time and prevents design errors, thereby reducing product costs. All Samacsys component libraries (schematic symbols, PCB packages, and 3D models) are free and follow strict industrial IPC package standards. You can download and install these libraries from ComponentSearchengine.com, or you can install them directly with the supplied CAD plugins. I use Altium plug-ins, almost all electronic design CAD software is supported, such as Eagle, Kicad, Orcad, Proteus, etc. [7].
(Supported CAD software)
(Select the component library in the Altium plugin)
Fourth, assembly and testing
1, assemble
The smallest component package is 0805. It also takes four 5mm FF gaskets to secure the LCD on the PCB board.
(From the top to display the packaging PCB board)
(At the bottom display assembled PCB board)
Connect the antenna to the board using the UFL to the SMA-F connector.
(UFL to SMA-F connector)
2, test
The lower limit of the frequency is 76.0 MHz, the upper limit is 108.0 MHz. You can increase or decrease the frequency by pressing or decreased by 0.1 MHz by pressing the up and down button. Similarly, if you press these buttons, the frequency will increase / decrease continuously. Therefore, it is easy to secure the receiver on the desired frequency (FM). In addition, the Scan button automatically searches for powerful FM stations and secures the receiver on the frequency. To search for the next station, press the Scan button again. Be
The intensity of the FM signal is displayed on the LCD screen in a bar chart. In the figure, the receiver has been set on the powerful FM radio, and the frequency is 100.0 MHz. Be
V. Material list
Correction: The value of R7 is 0R (1206). It is best to use TS2940 CW50 (SOT-223) for IC1. Use 8 ohm speakers to prevent IC1 regulators from being generated at high output power, or use a more powerful regulator.
refer to
[1]: TEA5767 Data Sheet: https://www.sparkfun.com/datasheets/wireless/general/tea5767.pdf
[2]: TEA5767 Schematic symbol, PCB size and 3D model: https://componentsearchengine.com/part-view/tea5767hn%2Fv3%2C118/NEXperia
[3]: PAM8403 Data Sheet: https://www.mouser.com/datasheet/2/115/pam8403-247318.pdf
[4]: PAM8403 Schematic symbol, PCB size and 3D model: https://componentsearchengine.com/part-view/pam8403dr/littelfuse
[5]: TS2937 Data Sheet: https://www.mouser.com/datasheet/2/395/TS2937_D13-522475.pdf
[6]: TS2937 Schematic symbol, PCB size and 3D model: https://componentsearchengine.com/part-view/ts2937cw-5.0%20RP/TAIWAN%20Semiconductor
[7]: CAD plugin: https://www.samacsys.com/library-loader-help
https://drive.google.com/file/d/1qvjslo2colzj8L9BU_MT4Y1MUGPO3K-S/View?usp=sharing
Sixth, update
Change the part number of the IC2 regulator and modify the PCB. The new regulator (L7805-D2PACK) is easy to find in the market. Please use 8 ohm speakers to prevent IC2 (regulator) from being thermally stressed at high amplifier output power, and do not apply more than 9V voltage to the input.
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