Read: How to make auto scan FM radio receiver for more details the infrastructure of the BK1079 IC
Most of the FM radio circuit that I've seen on YouTube and Google usually involve quite complicated components that require special variable capacitors and also the winding coil antenna. The most difficult part of those radio making is the winding coil that need to be specifically wounded to match certain frequency that could take long hours of testing and experiment to ensure it works.
Here is the simplest version of FM Radio circuit that I've tested that require least number of components to make it work and all of them are common and cheap to get except the micro-chip IC BK1079 which is quite rare to get. The circuit solely dependent on the micro-chip IC to fine tune the frequency according to the FM signal transmission channels. There is no need for complicated component and in fact even an antenna is optional. As long as you are within range to receive radio signal than it works perfectly fine 100% guaranteed.
This radio circuit will work inside a room even without antenna required.
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Step 1: The Required Component
You will the following components
BK1079 the primary IC that process almost everything - This IC consist of the following internal engineering structure in it
- Low Noise Amplifier (LNA) on the antenna side pin 6
- Programmable Gain Amplifier (PGA)
- Analog Phase Locked Loop (APPL)
- Digital Phase Locked Loop (DPLL)
- Analog to Digital Converter (ADC)
- Auto Gain Control (AGC)
- FM Demodulator
- Digital to Analog Converter at the output
Even without the digital phase locked loop (digital phase detector) the radio would still work - although it maybe less efficient in signal capturing
3 pieces of temporary switch push button the function are as follows
- 1 Switch to reset the FM channel on pin 2 of the IC
- 1 Switch to search FM channel on pin 10
- 1 Switch to control volume
3 pieces of 10 kOhm resistors
18 pF inductors
100 nH inductor
2 pieces 100 nF capacitors
1 Piece 10 uF / 50 volt Electrolyte capacitor
3 volts battery
Step 2: The Schematic Diagram
Please see the schematic diagram. The one marked with "X" are not necessary and we can remove them from the circuit. The reason being as follows
We only need auto-seek button that search upward without searching down. If the channels are not found we can keep searching up. Otherwise we can reset the search.
Secondly there is no need for volume down button and we only need volume increase. As we satisfy with loudness we can stop increasing the volume. Otherwise we can reset back to square one using the reset button
The Ferrite bead FB1 component is not necessary - it actually used to filter noise but without it the radio still work fine. And in fact if your connection (soldering) is bad the Ferrite bead could actually degrade power to the output causing the radio less sound.
Step 3: BK1079 Surface Mount (SMD) Soldering
This part require a little bit of experience to solder the BK1079 SMD IC to the through hole adapter board. The IC package type is MSOP-10 which (Micro small outline package). You can buy 10 pins through hole adapter for it more pins like 12, 16, 18 can be used as well. You just need to solder then on 10 pins pad.
You may need flux, Isopropyl Alcohol to solder it on the adapter board and use the solder pump to remove the excess solder that most likely to form bridge joint which you don't want it to happen.
Always use clean solder tips and ideal temperature.
Step 4: Assembly / Soldering the Component
Once the BK1079 is successfully soldered on the through hole adapter board. Then continue with the assembly of all the components. On this stage you can choose either to use permanent circuit board which is more efficient in terms of current / signal flow or you may choose to use breadboard just for initial experiment like i did on the video.
Using a breadboard is not as bad as you think - the video is the living proof for your reference to prototype the radio circuit first before soldering it on permanent board.
One additional advice is if you want the radio to play perfectly well - get a crystal as in the schematic tech spec. The function of the crystal is to provide DPLL (Digital Phase Locked Loop) and then combine it with the APLL (Analog Phase Locked Loop) to provide greater efficiency in the signal reception. However this is optional once you have successfully understand the basic of the circuit perhaps this is your grand step to improve the radio.
After all the circuit is done you can do the testing - not very difficult just keep pressing the seek button until you found audible channels. That's it you have made FM radio receiver.