More project photos (2)
The problem
This mini FM transmitter broadcasts live voice over a short range to any ordinary FM radio receiver tuned to the same frequency. An electret microphone captures speech, an audio amplifier raises that weak microphone signal to a level the transmitter stage can use, an oscillator circuit generates a radio-frequency carrier in the FM broadcast band, and the audio signal modulates that carrier so its frequency shifts with the voice. A short wire antenna radiates the modulated carrier, and a nearby FM radio demodulates it back into audible speech. The Arduino board in this build acts only as a 5 V power supply platform for the transmitter stage; it neither generates nor controls the oscillation, which is set purely by the coil and trimmer capacitor of the LC tank. Students can therefore trace a complete broadcast chain on one bench: sound in, a modulated radio signal out, and sound out again at the receiver.
This is a built-to-order hardware project: the transmitter prototype, microphone and oscillator stages, tuning procedure, and the complete viva kit (report, PPT, Q&A) are prepared fresh for you.
Comparison: transmitter against alternatives
| Option | What it does | How it differs from this transmitter |
|---|---|---|
| This mini FM transmitter | Sends live voice out as an FM radio signal from a microphone | It transmits; any ordinary FM radio nearby receives it, with no pairing or network needed |
| FM radio receiver project | Receives existing FM stations and plays them through a speaker | It only receives; it cannot send voice, which is the whole point of this transmitter build |
| Bluetooth audio link | Streams audio between two paired devices over a short digital link | It needs pairing and a compatible receiver, and it teaches digital audio streaming rather than FM modulation |
| Wired audio amplifier | Amplifies microphone or line audio into a speaker through a cable | It keeps audio on a wire; it radiates nothing, so it teaches amplification only, not radio transmission |
Converts voice into a small electrical audio signal.
Follow the working sequence
How it works
Voice enters the system at the electret microphone, which converts sound pressure into a small electrical audio signal. That signal is too weak to modulate a carrier directly, so an audio amplifier stage raises it to a usable level and sets its amplitude with a preset control. The amplified audio is fed to an oscillator and modulator stage built around a BC547 transistor, a hand-wound coil, and a trimmer capacitor; the LC tank alone sets the carrier frequency, and the audio voltage shifts that frequency up and down, which is frequency modulation. The resulting FM carrier is coupled to a short wire antenna that radiates it over a short range. A nearby FM radio receiver, tuned to the same frequency, picks up the carrier, demodulates it, and converts the frequency variations back into the original voice through its speaker. Power, grounding, and tuning determine how clean that recovered audio sounds.
- Speak into the electret microphone, which converts voice into a small electrical audio signal.
- The audio amplifier stage raises that signal and the preset control sets a clean modulation level without overdriving the oscillator.
- The oscillator stage, built around a BC547 transistor, a hand-wound coil, and a trimmer capacitor, generates a carrier in the FM broadcast band.
- The amplified audio shifts the oscillator frequency up and down with the voice, producing a frequency-modulated carrier.
- The modulated carrier is coupled to the wire antenna, which radiates it over a short range.
- An ordinary FM radio receiver tuned to the same frequency picks up the carrier and demodulates it back into voice through its speaker.
- Tune by slowly adjusting the trimmer capacitor while listening on the receiver until the audio is clearest, then recheck after warm-up and mark the tuned position.
Builder note from this build: final tuning is done in two moves, not one — spreading the coil turns slightly raises the transmitted frequency and squeezing them together lowers it, so the builder first sets the rough frequency with coil spacing and then fine-tunes with the trimmer capacitor. Handling the board after tuning can shift the frequency, which is why the tuned position is marked and rechecked before a demonstration.
Tech stack:
- Arduino board · 5 V power supply platform only, no oscillation control
- Electret microphone · voice capture at the audio input
- Audio amplifier stage · microphone signal amplification and level control
- BC547 transistor oscillator · FM carrier generation and modulation
- Hand-wound coil · frequency-setting inductor tuned by turn spacing
- Trimmer capacitor · fine frequency tuning control
- Wire antenna · short-range radiation of the FM carrier
- FM radio receiver · off-the-shelf receiver used for tuning checks and playback
| Parameter | Value |
|---|---|
| Transmitter type | Mini FM voice transmitter · single audio channel (design target) |
| Operating band | 88–108 MHz FM broadcast band (standard band value) |
| Range | Up to 10 m indoors · up to 30 m line-of-sight (design target) |
| Audio input | Electret microphone · voice input (design target) |
| Modulation | Frequency modulation · audio shifts the carrier frequency (design target) |
| Oscillator | BC547 transistor with LC tank · coil plus trimmer capacitor sets the carrier frequency (design target) |
| Antenna | Wire antenna · approximately 75 cm length at 100 MHz quarter-wave (design target) |
| Tuning | Trimmer capacitor plus hand-wound coil · manual tuning (design target) |
| Power | 9 V battery pack or 5 V USB supply (design target) |
| Output | FM carrier received by any ordinary FM radio (design target) |
| Not included | Long-range broadcast · stereo transmission · digital frequency display (not in this build) |
Project features
The transmitter's core capabilities are live voice broadcast, manual frequency tuning, and a fully traceable analogue signal chain. Speech picked up by the electret microphone is amplified and frequency-modulated onto a carrier in the FM broadcast band, then radiated by a wire antenna so any ordinary FM radio nearby can receive it without pairing, apps, or a network connection. Tuning is manual: a trimmer capacitor and a hand-wound coil set the carrier frequency, and the builder tunes by listening on a receiver until the audio is clearest, which teaches oscillator behaviour directly. The build runs from a battery or USB supply, stays deliberately low-power and short-range, and exposes every stage — microphone, amplifier, oscillator, antenna — as a separate test point for measurement and viva discussion. That separation also makes fault-finding straightforward during testing and demonstration.
- [Live voice broadcast] Speech into the electret microphone is transmitted as an FM signal and played back by any ordinary FM radio tuned to the same frequency. Implemented in the base prototype.
- [Manual frequency tuning] A trimmer capacitor plus a hand-wound coil set the carrier frequency, tuned by listening on a receiver until the audio is clearest. Implemented in the base prototype.
- [Audio amplifier stage] A small amplifier raises the weak microphone signal to a level that can modulate the oscillator cleanly, with a preset control for level. Implemented in the base prototype.
- [Wire antenna output] A short wire antenna radiates the modulated carrier over a short range, sized as a quarter-wave element for the tuned frequency. Implemented in the base prototype.
- [Arduino power supply platform] The Arduino board supplies 5 V power to the transmitter stage from a USB or battery input and anchors the prototype layout; it does not set or control the oscillation frequency. Implemented in the base prototype.
- [Battery or USB power] The prototype runs from a battery pack or a USB supply, so the demonstration works on a bench or a viva table without mains wiring. Implemented in the base prototype.
- [Bench test points] Microphone, amplifier, oscillator, and antenna stages are laid out as separate measurable points for signal tracing. Implemented in the base prototype.
- Optional: a wired line-level audio input for music playback from a phone headphone output, agreed before the build. Future scope: a digital frequency display and a varactor-based electronic tuning control.
What is included
- Working prototype: Arduino board, electret microphone, audio amplifier stage, BC547 transistor oscillator with hand-wound coil and trimmer capacitor, wire antenna, and battery or USB power, assembled and tested
- Tuning procedure: coil-spacing rough tuning, trimmer fine tuning, receiver-based clarity check, warm-up recheck, and marking the tuned position
- Circuit and wiring documentation with labelled connections for every stage
- Component list with the exact parts used in the build
- Demonstration procedure, including speaking into the microphone and playing the voice back on a nearby FM radio
- Project report PDF (background, FM modulation theory, oscillator design, methodology, limitations)
- PPT presentation for final review
- Viva Q&A preparation document (FM modulation, oscillator tuning, antenna basics, legal short-range limits)
Limitations & prerequisites
- Tuning drifts: the oscillator frequency moves with coil handling, trimmer position, supply voltage, and temperature, so the tuned position must be rechecked after warm-up and before a demonstration.
- Audio quality is voice-grade and mono: the prototype carries speech clearly over a short range but does not match the fidelity of a commercial FM station, and background noise in the room reaches the microphone.
- Interference cuts both ways: nearby FM stations, electrical noise, and other transmitters on the same frequency can degrade reception, and this transmitter must never be tuned to interfere with a licensed station.
- Legal short-range limit: this is a low-power, short-range, personal and educational build only — it is not a broadcast station, it must not be used for long-range or public broadcasting, and the builder must check current Indian wireless rules before transmitting.
- Range is short by design: walls, bodies, and antenna orientation reduce the usable distance well below the open-air design target, so demonstrations should stay in one room.
- The prototype is a bench demonstration model: it carries no broadcast licence or equipment certification, and it must not be presented as a commercial transmitter.
Frequently Asked Questions
What does this transmitter actually send, and what receives it?
This project transmits audio as an FM radio signal, and any ordinary FM radio receiver tuned to the same frequency plays it back. The Arduino board supplies power to the build, the electret microphone captures voice, the transmitter circuit modulates that audio onto a radio-frequency carrier, and a short wire antenna radiates it over a short range. The receiver is not part of the build — a phone with FM radio, a portable radio, or a car radio serves as the receiver.
Is this project suitable for a final-year project?
Yes, this project fits final-year work in Electronics and Telecommunication because it combines analogue audio circuits, oscillator design, frequency modulation, antenna basics, and hands-on tuning into one working demonstration that a student can explain, measure, and defend in a viva. It also gives a clean measurement story: carrier frequency, tuning behaviour, and recovered audio quality can each be checked during the demonstration.
How far will it transmit, and is it legal to use?
The design target is short range only, roughly a single room indoors or a few tens of metres with a clear line of sight, and it is intended strictly for low-power personal and educational use. It is not a broadcast station, it must not interfere with licensed FM stations, and the builder must check current Indian wireless rules before transmitting. Keep the power low, the range short, and the use personal or educational.
Why does the tuning drift, and how do you fix it?
Tuning drifts because the oscillator frequency depends on a hand-wound coil, trimmer capacitor settings, supply voltage, and temperature, so small changes in any of them move the transmitted frequency. The build therefore tunes by slowly adjusting the trimmer capacitor while listening on a nearby FM receiver until the audio is clearest, then rechecks after warm-up. Marking the tuned position keeps the setting recoverable after handling.
Can it play music from a phone instead of a microphone?
Yes, an audio source such as a phone headphone output can feed the same audio amplifier input through a suitable cable and level adjustment, replacing the microphone signal for music playback. The microphone stage stays in the base build, so a wired audio input is an optional variation to agree before the build, not a second transmitter. Keep the input level low so the oscillator is not overdriven.
What will I receive with the project?
You receive a working transmitter prototype with its Arduino board, electret microphone, oscillator and coil stage, audio amplifier, and wire antenna, plus power-supply wiring notes, circuit and wiring documentation, a component list, a tuning procedure, a project report, a presentation, and viva preparation material. The demonstration procedure shows how to tune the transmitter and play voice back on a nearby FM radio.
Components & software requirements
- Arduino board · 5 V power supply platform only, no oscillation control
- Electret microphone · voice capture at the audio input
- Audio amplifier stage · microphone signal amplification and level control
- BC547 transistor oscillator · FM carrier generation and modulation
- Hand-wound coil · frequency-setting inductor tuned by turn spacing
- Trimmer capacitor · fine frequency tuning control
- Wire antenna · short-range radiation of the FM carrier
- FM radio receiver · off-the-shelf receiver used for tuning checks and playback
Delivery information
Built-to-order project. Delivery timeline is shared after order confirmation based on current queue.
Support terms
Complete documentation, setup guide, and viva preparation included. Support for setup and explanation provided.
Download free synopsis (PDF)
Enter your name and WhatsApp number — the synopsis PDF downloads immediately. We may send occasional project updates on WhatsApp; no spam.