DIY: Assembling an FM Radio Kit
FM radio is quite popular these days and there are many FM channels available in most of the cities. If you live away from a city or wish to get signals from a distant station, an outdoor antenna can be used to improve the signal reception. We will start off by assembling an FM radio kit which is available in local electronics spare shops. This FM radio board uses CXA1619BS integrated circuit. CXA1619BS is a 30 pin integrated circuit with 15 pins on either side. It is a specialized integrated circuit which can be used to receive both frequency modulation or FM and amplitude modulation or AM radio signals. In this FM board the IC is responsible for FM signal processing and has functions of radiofrequency amplifier, oscillator and mixer. It also incorporates intermediate frequency or IF amplifier and quadrature detection. Audio extracted by demodulation is amplified further in the audio frequency amplifier section.
CXA1619BS is an SDIP device, meaning that it is a Skinny dual in-line package meant for through the hole mounting while CXA1619BM is an SOP or small outline package IC with 28 pins for surface mounting. Recommended supply voltage for for CXA1619BS is 2 – 8.5 Volts. It can provide an output of 500 mW to an 8 ohms loudspeaker with 6 Volts supply voltage. Pin numbers 1, 2, 29 and 30 are ground pins. Audio frequency output is from pin 28 and supply (Vcc) is given to pin 27. Audio frequency input is at pin 25. Central pin of the volume control potentiometer is connected to pin 5 of CXA1619BS. All these and many more details, including an electrical characteristics test circuit and a couple of application circuits are available in datasheet of the device from the manufacturer.
Variable capacitor or tuning capacitor seen on this FM board is used for tuning in the desired FM station. Various inductors and capacitors are used for filtering the radiofrequency signals. Signals are received through the blue wire which can be connected to a wire antenna.
I am using a battery box with four AA batteries to provide 6V power supply along with a simple switch. The red and black wires from the FM board are for power supply.
I am using an 8 ohms speaker, which was bought separately, along with the loudspeaker enclosure. Yellow and green wires from the FM board can be used to connect to the loudspeaker. This FM board gives good audio output by itself and an additional audio amplifier can be connected if needed.
Solder wire and flux needed for soldering the wires to loudspeaker, power supply and volume control.
This is the low power soldering iron which I use for soldering electronic components and connections. Tip can be cleaned using a sponge after each use, once you dip it in the flux. They say that using a sandpaper or knife edge to clean the soldering tip is not the ideal way.
Here I have soldered the yellow and green wires coming from the FM board to loudspeaker terminals.
Red wire has been soldered to one side of the switch. Other side of the switch is connected to the red wire coming from the battery box filled with four AA batteries, to provide 6 Volts. Black wire from the FM board has been connected to the black wire from the battery box, which is the negative supply terminal. You can also see a thick green wire antenna connected to the thin green wire from the FM board using a pair of crocodile clips attached to a piece of yellow wire.
That was the hissing noise from the FM receiver when the circuit was switched on.
That was a test reception of a local FM station with the wire antenna kept elevated. Station was selected by careful tuning using a tuning knob attached to the variable capacitor on the FM board meant for tuning in the station.
That was another test reception with the antenna wire kept on the bench and held at the bare tip of the copper wire inside.
This was another test by just holding the insulated copper wire antenna without touching the bare tip. These are the initial steps of assembling the DIY FM radio board with additional components purchased along with. Next steps are connecting the volume control and installing the loudspeaker inside the enclosure. Still later I am planning to test different types of indoor and outdoor antennas to improve reception of multiple stations. Stay tuned to this channel for updates.