Make FM radio step by step

Greetings, friends! I want to tell you about the module that is a ready-made radio receiver that receives frequencies of 64-108 Mhz (FM band). I bought it on aliexpress for $ 1.73 for experiments and assembling a portable radio. The topic of "radio" I'm concerned about, they are kind memories from my childhood, when my father first collected detector receivers, then digital ones on different microcircuits. There was interest, with each new scheme I wanted to get a better and miniature design. It seems to me, the top of this, in my understanding, can be considered a purchased module! It's very cheap, tiny sizes, low power consumption, it does not need to debug the circuit and is fully ready for use right after power is applied, and any newcomer can handle it.

I propose to take a closer look, a top view.

Bottom view.

For scale it is a photo with a coin of 10 Russian cents (coin diameter is 17.5 mm).

The module uses the AR1310 digital chip, made in China. Therefore, I could not find full datasheet on it, it is known only that it is a single-chip stereo receiver in which a audio amplifier is already built in. It also has a low power consumption from 2.2 to 3.6 V.

Specifications AR1310

Dimensions and pin mapping

Typical connection diagram of the module

The diagram shows that you need a minimum of details. Actually, the buttons for volume control, station tuning and the on / off button.
An antenna can serve as a piece of wire length of 37 cm (this will be a quarter of the wave at a frequency of 100 MHz). Condenser C1 serves as a filter for the supply voltage. Now refinement over C2 and C3: these capacitors serve to cut off the DC component and can be from 10 to 470 uF. You can do without them at all, then the built-in amplifier will give out a full range of low frequencies to the headphones, but the current consumption will be around 80 mA (depending on the resistance of the headphones). I tried to put a capacity of 10 uF, sound cuts low frequencies, but the current consumption was only 20 mA, which is almost 5 times less than without capacitances. For autonomous power supply it is essential! If you collect the design, I think, the nominal values of C2 and C3 will be selected independently.

Next, I'll describe the build process a little. Conclusions soldered to contact pads.

On the textolite I do "flying", it turned out not very aesthetically, but it will work for the test. There is a variant without capacitors C2 and C3.

The second version with capacities of 10 uF.

I turn on the power, and connect the headphones. After pressing the power button, everything worked without problems. The volume in the headphones is amazing. Searching and switching between stations is fast, less than 1 second. The on / off button takes the receiver to sleep, if the power supply remains, then the power is on the same radio station.
By the way, using a miniature element base, the board size can be reduced by 2 - 2.5 times!

I also made electrical measurements. The current consumption in the sleep mode is 16 μA and in the working 16.9 mA (without the connection of headphones).

Now measurements without C2 and C3. With a load of 32 Ohms, the current was 65.2 mA, with a load of 17.5 Ohm - 97.3 mA.

I set C2 and C3 to 10 uF. Measured the current consumption (at a voltage of 3.3 V), as we see, the result is obvious. At a load of 32 ohms - 17.6 mA, with 17.5 ohms - 18.6 mA.

Brief conclusions:

1. The price of the module is less than two bucks.
2. To build a full radio receiver you need a minimum of details (buttons, a pair of resistors and a piece of wire).
3. The complexity of assembly is minimal, any unprepared person will cope.
4. Overall dimensions and power consumption allow to build such a module, for example, even in a wristwatch.

On this, perhaps, everything, I will be glad to answer all questions concerning work and assembly.

Sincerely, @gleb-jeglov aka Evgeny