If you have ever wanted to listen to your MP3 player’s music on a stereo but lacked the proper connection equipment, you can overcome this obstacle with a simple FM transmitter that will broadcast your MP3 player through any nearby radio. While such transmitters are available commercially, building your own is a useful project for those with intermediate soldering skills and a desire to learn about radio frequency technology. The most difficult part of the project will be the soldering, because the components and the circuit board are so small.

There many ways to design an FM transmitter circuit, but “Elektor Magazine” has published project schematics that fit all the necessary components on the smallest printed circuit board possible. Hobbyists may choose to either build their transmitter according to “Elektor Magazine’s” circuit diagram, modify it or build a completely different circuit of their own. This article discusses building the circuit as found on the “Elektor Magazine” website.

Instructions

1.Prepare the printed circuit board. Before assembling, clean the copper pads gently with rubbing alcohol. Heated solder tends not to adhere correctly to dirty pads, thus creating weak electrical connections. After cleaning, mount the PCB with alligator clips or some kind of helping-hands device that will allow you free use of both hands for soldering.

2.Install the capacitors. There are eight capacitors in all, ranging from 2 nanofarads to 4 microfarads. Like all the components on this board, these are very small, surface-mount design (SMD) pieces. SMD components don’t have wire leads that poke through the PCB, leaving you to solder from the underside. These capacitors require a small bit of solder at each end.

3.Install the SMD resistors. Six of the eight resistors for this device are standard resistors, but two are variable resistors that are adjusted by screwdriver. One of these variable resistors is used for setting the volume while the other sets the broadcast frequency.

4.Install the inductors. These small components are basically coiled wires that store electricity. Their coiled shapes help to intensify the magnetic field around the inductor.

5.Install the integrated circuit. In this case, you are soldering a surface-mounted chip, the MAX2606EUT+ from Maximum Integrated Products. Instead of using the usual protective socket, you are soldering the chip directly to the board. Be care not to overheat and damage the chip while soldering.

6.Install the stereo audio jack. This jack is the input that takes the cable from your MP3 player. The audio signal comes in through the jack, is process by the circuit and is transmitted to any nearby radio set to the correct frequency.

7.Install the USB connector. The only purpose of this connector is to power the FM transmitter circuit. You can plug the unit into a computer or any other device with a USB port.

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