How to Make an FM Modulator

FM modulation entails taking a signal and transferring it to a different type of signal to be transmitted. With an FM modulator device, you can hook up your MP3, satellite receiver or iPod to the radio channel in your car and listen to your favorite music.

Things You'll Need

• FM stereo transmitter kit
• Wiring diagram
• Wire cutters
• Fine sandpaper
• Soldering iron
• Electrical tape
• Screwdriver

Instructions

Make an FM Transmitter

1. Lay out the printed circuit board on your workbench. Set the rest of the circuit components supplied on your workbench for easy access.

2. Refer to the schematic (circuit diagram) to identify where you will install each component to your printed circuit board.

3. Clean the metal pins that fix into the printed circuit board of the circuit components (leads) with fine sandpaper. Bend the leads gently and fix then into the holes on the printed circuit board.

4. Attach the circuit components to the board. Melt a solder wire where the leads emerge from the board using a lightweight fine-tipped soldering iron set to about 25 watts.

5. Install your transmitter’s circuit board into the transmitter’s housing and attach the remaining components.

Fix the FM modulator

1. Take out the faceplate on your car’s stereo unit. Pull out the stereo from its compartment to access the wiring panel.

2. Study the wiring in your car. Locate the ground wire (green) and hot wire (red) of your FM transmitters. Select the ground wire and attach it to antenna wire housing with electrical tape.

3. Connect the hot wire (red) from your car’s wiring panel. Peel back the plastic sheath of the wire for about half an inch. Intertwine it with the bare section of your FM transmitter’s red wire. Wrap electrical tape around your interlinked wires.

4. Connect one-eighth inch converter cable (RCA connector cable) from your portable media device’s (iPod or MP3) to the FM transmitter. One end of the cable has a standard one-eighth inch headphone jack while the other has red and white outputs (You can easily obtain this cable from an electronic store). Connect one-eighth inch end to your portable media device’s headphone jack. Connect the RCA connector cable to the RCA audio inputs on your FM transmitter.

5. Set a channel over which your FM transmitter can modulate (convert) the signal from your MP3. The channel you select will determine the frequency you will have to tune your radio to listen to music from your MP3 player.

6. Insert the FM transmitter and the wiring harness into your car stereo’s compartment on the dashboard. Replace the stereo unit to its compartment. Put the faceplate back onto the front of your stereo unit and screw in the cradle screws to hold it in place.

7. Attach your secure mount to the dashboard or to any accessible place in your car. Secure your portable media device to the secure mount. The secure mount will securely hold and display your MP3 or iPod in place since you don’t want them falling to the floor of your car.

8. Turn on your car radio and tune to the selected channel. For instant, if you selected a channel that corresponds to 92.3 FM, tune your radio to 92.3 FM. Turn on your iPod or MP3 player and listen to your favorite music via your car stereo speakers.

References

• ESP: Low Power FM Transmitter
• PKYS: Standards, Tables, International Equivalents
• Trans Local: Making the simplest Transmitter
• Hewlett Packard: Digital Modulation in Communications Systems