The module is based on a HEX3653 IC which is essentially an FM radio chip that can receive modulated FM signals with a frequency range of 76 to 108MHz. It uses very few external components such as: control buttons, resistors, capacitors, transistors and LEDs. The buttons allow the volume adjustment (VOL- and VOL +), the station search (SEEK- and SEEK +), switch the device on or to standby (PWS). The tuning ranges between 76 and 108 MHz in steps typically 50 kHz, the extension of the tunable FM band has been designed to cover all the frequency-modulated radio bands in the world. In Italy and generally in Europe the FM range typically ranges between 87.6 and 108 MHz. It also has a 3.5 mm stereo jack for listening to headphones and a pin-strip connector, which allows connection to an external stereo audio amplifier. As an antenna, either the headphone or earphone wire can be used (exactly as with the FM radio built into mobile phones and smartphones) or a separate antenna (wire or stylus).

Note. Batteries, headphones and antenna not included

• Required input voltage: 3 Vcc
• Current consumption: 30 mA
• Tunable frequency: 76÷108 MHz
• Headphone output: 32 ohm
• Audio output: 200mVeff
• Modulation: FM
• Decoding: stereo with 35 dB separation
• Digital sintony: with buttons
• Volume control: digital

It is a complete FM radio receiver in CMOS technology encapsulated in a 16-pin SOP plastic case, with a quartz digital synthesis tuning stage (using 32.768 kHz quartz) with 40 dB AM rejection, stereo multiplex decoder and digital volume control .

The component of the component is completed by an LDO regulator that obtains the stabilized voltage for all stages, starting from the applied voltage between the Vcc and the GND.

The chip feeds between 1.8 and 3.6 Vdc and typically absorbs 17 milliamps (without the LED) with outputs connected to a high impedance stage.

The stereo output is coupled in continuous (not by chance requires decoupling capacitors) and is low impedance and typically accepts loads from 32 ohm to 1 kHz, ie it can be connected to high impedance inputs of preamplifiers and audio amplifiers.

The stereo decoder allows a good separation of the channels, typically 35 dB, while the audio outputs guarantee a low harmonic distortion, which ranges between 0.05% and 1% at maximum volume. The signal to noise ratio reaches around 60 dB, so it is more than acceptable.