Single Transistor FM Transmitter (500m Range)

In this electronics project, I will show you step by step to make a mini FM Transmitter using single transistor.

Yes! this is really mini where the circuit can run at 1.5 volt and can be used as a long-range spy.

Let's make it!

Step 1: Components list

The following components are needed to make this transmitter circuit.

• Q1: Any NPN Transistor - BC547, BC548, 2N2222, etc. (1 pcs)
• R1: 4.7Ω Resistor (1 pcs)
• R2: 100Ω Resistor (1 pcs)
• R3: 10KΩ Resistor (1 pcs)
• L1: 28G Copper Wire (1 pcs)
• C1: 30pF Capacitor (1 pcs)
• C2: 0.01nF Capacitor (1 pcs)
• C3, C4: 0.01µF Capacitor (1 pcs each)
• C5: 1µF Electrolytic Capacitor (1 pcs)
• M1: Electret Condenser Microphone (1 pcs)
• Small Veroboard (1 pcs)
• B1: 1.5V Battery (1 pcs)

Step 2: FM transmitter Circuit diagram

Schematic of single transistor FM transmitter circuit shown below.

Circuit explanation

The circuit is simple and easy to make.

An FM transmitter is a low-power FM radio transmitter that broadcasts a signal wirelessly with a specific frequency to a standard FM radio or mobile device.

The main component of this circuit is a single transistor and a coil.

Here, you can use any NPN transistor (Q1) as your wish (I used here BC547).

This transmitter cool part is a coil, take 28 gauge copper wire and warped five-time and the coil has been created.

Note: If you the making this coil the wrong way you can never create this FM Transmitter. The correct rule is to be this coil will have the same straight line with both legs where the coil weight is 5mm, and height is 4mm.

A capacitor (C1) is used to keep the coil frequency.

The resistor (R1) connected from V_IN positive to transistor base pin that reason to active the transistor (Q1).

To filter transistor base volt, the capacitor (C2) connected with the base pin and ground.

The capacitor (C3) between the collector and emitter influences the voltage on the emitter to turn the transistor on and off. It does this by constantly monitoring the voltage on the tuned circuit and passing the change to the emitter.

The negative voltage to the transistor emitter pin can be done through the resistor (R2) for a little bit volt.

The capacitor (C4) used to filter the battery (B1) voltage.

The input voltage is 1.5V and perfect for this circuit, entering more than 1V will destroy the transistor (Q1).

The reason a negative volt is entered into the emitter pin and the V_IN positive volt entering the collector pin.

To transmit an audio sound or music through this FM transmitter a condenser microphone (M1) connected base pin through capacitor (C5) and ground.

A safety resistor (R3) is connected to the condenser positive teminal to the V_IN.

Step 3: Assembling and Soldering Components

Now, I put the components one by one on a small Veroboard and soldering it according to the schematic.

After soldering all components, I connect a 1.5V battery to the FM transmitter circuit board as an input supply.

Also, I simply connect an RC Antenna for large distance transmission.

Step 4: Demo & Testing - FM Transmitter

After powering the circuit board I start to scan the FM transmitter signal in my phone radio application.

Finally, I got the signal is 92.9 MHz!

But, when it transmits any audio sound or music through the FM transmitter, this process may change MHz.

The reason there is no crystal in it and you can see below that the MHz signal has changed to 9.06 MHz.

After tuning and selecting the 90.6 Mhz, I start to hear the broadcast sound from this homemade FM transmitter in my radio app.

Now, the question is how far will it work? — I keep walking around with the phone, and I saw the small single transistor FM transmitter working at 500 meters with the antenna.