Stereo FM transmitter from MP3 player

Not so long ago, a Chinese manufacturer developed this device for the happy owners of cassette recorders, who do not have enough money to buy a normal MP3 player.
Cheap and cheerful - it is relatively cheap (I took for 200 rubles), while it has several advantages including a remote control. It's simple: put it in the cigarette lighter, stuck a USB flash drive with your favorite music, tuned the radio to the transmitter frequency and that’s it! Clack from the remote without touching your hands from a distance.
I don’t have a car, but I decided to use this thing in my own way. Like a stereo transmitter. Why do I need it? And in order to broadcast sound from the laptop to the music center. The fact is that I like to watch a movie on the big screen, on the projector. I connect the video from the laptop to a straight line, and to connect the sound you need to pull a long wire to the center. That's to prevent this, I decided to get rid of the wires in my own way.

Bought, disassembled. Having made a peculiar bunch of details.

Share the device into two parts: a small board is a stabilizer. It reduces the voltage to 5 volts and accordingly stabilizes it. 3 wires go to it: two power wires and a third antenna (white in color). The big board with the display is the MP3 player itself.

We solder all three wires from a large board. We solder a longer wire for the place of the antenna wire to increase the radius of the transmission. We take the USB adapter and solder the power to the board from it as shown in the figure.

Next, connect the sound to the transmitter. We find the transmitter chip. Sound comes from the processor through a two-chip capacitor. We remove these capacitors, I just gently knocked them with a screwdriver. The work is painstaking. We solder two capacitors with a nominal value of 0.01 ... 0.1 μF to the output of the microcircuit and apply sound to them. The common wire is taken from the minus board. That's all. It would be nice to add a divider of resistors to each input, say 1: 2, otherwise the output of the laptop is more high-voltage than necessary. But then I realized it.

Close, check. Works!

Very comfortably! Our transmitter is also powered by a laptop. The quality is certainly not like through a wire, but pretty decent. Now, with the remote control, you can blame only the transmitted frequency, the rest has lost its power. I think there is nothing complicated here, anyone with little effort will do it himself without important problems.