Simple Stereo FM Radio Receiver Circuit

There are many simple RF receiver circuits available for AM/FM band. But the difficult part is making the coils and tuning the circuit. Without proper construction and alignment the circuit would not perform well.

This article explains how to build a simple stereo FM receiver without any tuning elements (inductors(L), variable capacitors(C) and ceramic IF filters).

The receiver is capable of receiving 76-108MHz FM band with stereo output having good sensitivity and performance. The output is capable of driving 32Ω speaker directly which eliminates additional audio headphone amplifier.

The heart of the circuit based on HEX3653/GS1299/RDA7088. We can use anyone of them. All of the above three ICs having same pinout and function.

The IC comes in SOP-16 package with 1.27mm lead pitch. We can either use a pitch converter breakout board for easy breadboard or veroboard or dotboard usage with 2.54mm pitch. We can also use SOIC-16 ZIF socket adapter with 2.54mm pitch for easy and quick experiments.

Features:

• Requires least external components
• Supports worldwide frequency band 76-108 MHz
• Less than 5s full band seek time
• Low cost 32.768kHz crystal for RCLK
• Digital Automatic Gain Control(AGC)
• Direct 32Ω spearkers driving capability
• Simple SOP16 package
• 1.8V to 3.6V DC voltage operation
• Low current consumption of 17mA at 3.0V

Schematic Diagram

BOM

Construction and Connections

We can construct using a Veroboard or breadboard. First we need to fix the IC using a 2.54mm adapter board or ZIF SOIC16 socket. For adapter board requires soldering skill to solder 16 pin 1.27mm pitch IC.

Connect all the GND(2,3,5,11&14) and VDD(6,10) pins as shown in the diagram.

Connect the 32.768kHz crystal one end to pin 9 and the other end of the crystal connected to GND.

Connect 5 push buttons to pin number 1,7,8,15&16 for POWER ON/OFF, SEEK-, SEEK+, VOL- and VOL+ functions respectivly. Resistor R1(10kΩ) and C3(100nF) are optional and not required.

Connect C1&C2(100uF/16V) to pin 12&13. The other end of the capacitors C1 and C2 can be directly connected to 32Ω speaker + terminal or connected to 3.5mm audio jack. If you connect 3.5mm audio connector then we can plug earphone or headphone of 32Ω resistance type.

For antenna connect 75cm length SWG#22 wire to pin 4 of the IC.

Inductor L1(100nH) and C6(24pF) forms the band rejector. The L1&C6 parallel combination allows 76-08MHz band and rejects below 76MHz and above 108MHz. L1&C6 improves the performance. But not mandatory if availability is an issue.

We can also use the earphone or headphone wire as FM input antenna.

For more details refer to the datasheet application circuit.

Connect C5(100nF) close to the pin 10 and GND.

Power:

We can provide 3V DC from 1.5×2 AA cells. Make sure the polarity of the power source while connecting the battery to the circuit. Else we can also provide 3.3VDC from 5V power adaptors with the help of using AMS1117-3.3 breakout board.

Operation:

There are only 5 possible functions available with this circuit.

1. POWER ON/OFF control using SW1(PSW). It is a toggle type input. Pressing once turns the radio ON. Pressing again turns the radio OFF.
2. Pressing SEEK- searches the next available channel towards 76MHz
3. Pressing SEEK+ searches the next available channel towards 106MHz
4. Pressing VOL- reduces the VOLUME
5. Pressing VOL+ increses the VOLUME

Depends on the signal strength the AGC provides consistent performance with reduced noise.

The overall performance of the FM stereo receiver is good compared to the cost and number of components required.