How to Build a Simple Arduino FM Radio Transmitter with a Range of 100 Meters

Building a simple FM radio transmitter with an Arduino is a fun electronics project that allows you to broadcast audio within a 100 meter range. With some basic electronic components and Arduino code, you can set up your own pirate radio station in no time. Here is a step-by-step guide on how to build an Arduino FM transmitter from scratch:

Gather the Required Electronic Components

To build the FM transmitter, you will need the following components:

• Arduino Uno - The brain of the transmitter that generates the FM signal.
• RF amplifier module - Boosts the output from the Arduino to achieve a higher transmitting range. A common one is the Avian 1W FM transmitter.
• Antenna wire - Around 20-30 cm long piece of insulated wire that radiates the FM signal.
• Capacitors - Two 22 pF capacitors for filtering the audio input.
• Resistors - A 1k and 10k ohm resistor.
• Audio cable - A 3.5mm audio jack to connect audio source.
• 9V battery - Power source for the Arduino and amplifier module.

Double check you have all the components before starting the build.

Assemble the Circuit

Here are the steps to assemble the circuit on a breadboard:

1. Connect the 10k resistor between Arduino pin 11 and ground. This sets the biasing for the oscillator.
2. Connect the two 22 pF capacitors in parallel to Arduino pin 9. These filter the audio input.
3. Connect the 1k resistor in series between Arduino pin 9 and pin 11.
4. Connect the RF amplifier module to Arduino pin 11. Make sure to connect the ground.
5. Connect the antenna wire to the amplifier output. Keep it straight.
6. Connect 9V battery to Arduino Vin pin and amplifier module.
7. Plug in the audio source to the audio jack connected to the capacitors.

Double check all connections before powering up the circuit.

Upload the Arduino Transmitter Code

Now that the hardware is ready, we need to upload the Arduino sketch to generate the FM transmission. Just follow these steps:

1. Download the Arduino FM transmitter code from this GitHub link.
2. Open the Arduino IDE on your computer.
3. Go to Sketch > Include Library > Manage Libraries and install the FreqCount library.
4. Open the downloaded Arduino sketch in the IDE.
5. In the code, change the stationID to your desired station name.
6. Select the Arduino Uno board and COM port.
7. Click upload to flash the code to the Arduino.

Once uploaded, the Arduino will start transmitting the FM signal.

Tuning and Using your DIY FM Transmitter

To tune your receiver or radio to the correct frequency:

• Set the receiver to the low end of the FM band ~88 MHz.
• Slowly adjust the 22 pF capacitors on the Arduino until you hear your station.
• Tune the receiver to the clearest signal.

Now you can start broadcasting your own FM radio station! Simply connect any audio source like your phone, MP3 player or computer to the audio input jack and it will be transmitted.

Improving the Range

The transmitting range depends on the antenna and amplifier used. To increase the range:

• Replace the amplifier module with a higher power one like a 3W or 5W FM transmitter module.
• Increase the antenna length and experiment with different antenna designs. A 1/4 wavelength whip antenna works best.
• Place the antenna higher by mounting it on a mast or roof (follow regulations).

With the right components, you can achieve a transmitting range of up to 300 meters or more. Just make sure to operate the transmitter legally within allowed FM frequencies.

So in summary, building an Arduino FM radio transmitter is an enjoyable and educational project for electronics enthusiasts. The parts are easy to source and with the right circuit design and code, you can start broadcasting in no time. Just be responsible and remain within legal transmission power limits.