we are going to show you how to make an FM transmitter using 3 2N2222 transistors. This transmitter will allow you to transmit your voice to a remote location.
This circuit is a great way to transmit sound without having to use wired connections. By
using this circuit, you will be able to transmit your voice without any lag
FM Transmitter Circuits: How To Build One Custom For You
Does your engineering project need an FM Transmitter Circuits, but you have no idea how to make one? Then this article is for you.
The FM transmitter circuit is a crucial part of wireless and Bluetooth communication circuit and carrier frequency projects. Moreover, it is efficient and can be tricky, due to its intricate diagrams and design.
Image showing a frequency modulation (FM) vector diagram
Fortunately, this guide will make your job easier by breaking down the big chunks of information and frustrating diagrams.
Therefore, make us comfortable and immerse ourselves.
1. What is an FM transmitter circuit
FM (Frequency Modulation) transmitter is an electronic circuit that manipulates a carrier signal wave to transmit useful information or data.
Also, it uses a single transmitter and does not require a massive power supply to transmit audio input signals over long or short distances.
For an FM transmitter circuit to work, you need a portable audio device like an MP3 player or a mobile phone.
Therefore, you can connect the transmitter to the headphone jack of your audio device and send sound signals on an FM band frequency.
Any radio station within transmission range can pick up any message signal.
2. How to make an FM transmitter circuit
Image showing an engineer creating an FM transmitter circuit
This section will show you how to create the simplest DIY FM transmitter circuit that works perfectly.
2.1 FM Transmitter Circuit Production Tools
Here are the things you need to make an FM transmitter circuit:
9v battery
variable capacitor
Antenna
Microphone or other audio input
Inductor
Resistors and capacitors
Transistors
2.2 Circuit diagram and description
If you're new to this, the circuit diagrams might look a bit confusing. But, don't worry, we're here to make it easy. Take a look at this handy diagram of a circuit.
This circuit diagram shows an FM transmitter with a 9v supply. Also, the microphone is the input device that receives the sound signals.
Therefore, you can generate sound radio wave signals when you speak into the microphone. Also, the microphone has capacitive plates that create energy from the sounds you make.
Then it varies the audio wave at the splitter junction and transforms it into audio signals. After that, the capacitor (C1) cancels the noise from the audio signal and sends it to the transistor (Q1).
The transistors send the sound signals to the LC tank circuit. Moreover, the circuit is necessary because it generates the motion of fixed frequency.
The audio signal from the transistor will then modulate the fixed frequency signal. Then the modified signal transmits to the antenna, which sends the sound signal to any receiver within 30 meters.
2.3 FM Transmitter Circuit Design
The FM transmitter circuit has different designs ranging from simple to complicated. So, let's look at two basic techniques that are common and easy to create.
2.3.1 Wireless design
The design of the wireless circuit sends signals that transmit through a radio tuned to the corresponding frequency band.
The frequency depends on how the inductor is placed and the values of C1, C2 and C3. Additionally, you can manipulate the distance or coil diameter to effect the perfect response on FM receivers.
A small wire antenna (about 3 inches) can be attached to the point shown to make the bug highly responsive and create distortion-free signals.
So here is the design of the wireless FM transmitter circuit.
2.3.2 Design of a transistor
This design is the simplest transmitter circuit to manufacture. However, its simplicity creates some drawbacks such as:
Small transmission range
It uses a 1.5V battery with limited capabilities
The single transistor design does not use a microphone as a sound input device. Instead, its antenna performs a dual function (it detects and transmits sound vibrations). Also, it has no frequency determining step. Thus, it cannot be called a tuned transmitter circuit.
Therefore, let's look at the cDesigning the parts you need to build an FM transmitter circuit.
2.3.3 Audio preamplifier design
This design depicts a preamplifier with a simple single-stage common-emitter amplifier.
Vdc selection
We chose the NPN bipolar junction transistor, BC109. Also, it has a voltage of around 40V, so we selected a smaller Vcc (9V).
Load resistor, R4
Diagram showing load resistance
Here calculating the quiescent collector current will give you the value of the load resistor. Thus, the collected voltage should be 1/2 of the selected Vcc. Again, this means that the value of our fixed load resistor, R4, is 4.5k. So we chose a 5K load resistor for maximum performance.
Voltage divider resistors R2 and R3
You can get the value of the voltage divider resistors by calculating the voltage across all the resistors and the bias current.
Moreover, the bias current has an approximate value of 10 times the base current. The base current (lb) here is 0.008mA – Therefore our bias current is 0.08mA.
Also, the voltage across the resistors (Vb) is assumed to be 0.7v higher than the emitter voltage (Ve). So, for example, if our Ve is 12% of the Vcc (1.08v), our Vb will be 1.78v.
Therefore, R2 = Vb/lbias = 22.25k. So we chose a 22k resistor.
R3 = (Vcc-Vb/lbias = 90.1k. So we chose a 90k resistor.
Emitter resistor R5
To obtain the value of R5, use the formula Ve/le. Le is the emitter current and has the same value as the collector current. Therefore, R5 = (Ve/le) = 540 Ohms. So we choose a 500 Ohm resistor because it can bypass the emitter current.
Coupling capacitor, C1
The purpose of the capacitor is to modulate the current flows through the transistor. Thus, large values show lower frequencies (bass) while lower values show higher frequencies (treble). Here we choose a value of 5uF for our C1.
Microphone resistor R1
This resistor limits the amount of current flowing through the mic so that it stays below the maximum the mic can handle. Also, if the maximum current value of our mic is 0.4mA, then the value of Rm = (Vcc-Vb)/0.4 = 18.05k. As it should be less, we choose an 18k resistor.
Bypass capacitor, C4
For the C4, we chose an electrolytic capacitor that bypasses the DC signal with a value of 15 uF.
2.3.4 Design of the oscillator circuit
Here is the design of a simple oscillator circuit:
Tank Circuit Components – L1 and C6: We need an oscillation frequency between 88 MHz and 10 MHz for this selection. Thus, we choose a capacitor in the range of 5 to 20pF. Using a 0.2uH inductor will give our C6 an approximate value of 12pF.
Tank Capacitor, C9: This capacitor aims to keep the circuit tanj=k vibrating. So we will choose a 5pF capacitor if our value is between 4 and 10 pF.
R6 and R7 Bias Resistors: Based on the calculations for the bias resistors in the preamplifier design, our R6 and R7 resistors will be 9K and 40K.
Coupling Capacitor, C3: We chose 0.01uF electrolytic capacitors for our coupling capacitor.
Emitter Resistor, R8: The emitter resistor will have an approximate value of 1K, based on previous calculations for the amplifier circuit.
2.3.5 Power Amplifier Circuit Design
FM transmitter circuits do not require high power output, so we chose a class A power amplifier with an LC tank circuit as the output.
Also, our tank circuit has the same values as that of our oscillator circuit. So we choose a bias resistor with a value of 20 K and a coupling factor of 10 pF.
2.3.6 Antenna Selection
The range of our FM transmitter circuit is about 2 km, so we choose a stick antenna that is 1/4th the transmitter wavelength. Other antenna options also include 30 inch wire.
2.4 Detailed steps
Here are four steps to guide you when creating your FM transmitter circuit.
2.4.1 Obtain required components
Make sure you have all the components you need before you start building an FM transmitter circuit.
So for this FM transmitter circuit you will need the 2N3904-2 transistors, five resistors: 100k Ω-1, 100Ω-1, 1M Ω-1, 1k Ω-1 and 10k Ω-3, a 0.1uH inductor , four capacitors: 0.1 pF – 2, trimmer 40 pF – 1, 4.7 pF – 1, 10pF -1, an antenna, a bNext, make your inductor out of 18 or 22 gauge copper wire. If using the 18 gauge copper wire, create a 4 to 5 turn inductor with 1/4 inch (oR). For 22 gauge, create an 8-10 inductor with 1/4 inch.
After creating your inductor, be sure to solder it to the circuit.
Solder your antenna to the circuit. So you can select 8-10cm patch wire as antenna or use standard antenna.
2.4.4 Transmitter Setup
Transmitter tuning is tricky and the process takes some time, so it requires patience and caution.
When you vary the trimmer capacitor, you can adjust the transmission frequency.
So slowly vary the capacity of the trimmer until you hear distortion. Then slowly tune into the distortion area until your transmitter matches the radio frequency. Then you will hear a clear output from the radio.
Once the tuning is complete, you will have a completed FM transmitter circuit.
3. FM transmitter circuits with its special functions
Here are some special functions of the FM transmitter circuit:
3.1. Circuit operation
When you turn on the FM circuit, the capacitor keeps the transistor from changing until it is charged.
Once the 22n capacitor is discharged, it turns off the transistors until it recharges – this procedure quickly generates a frequency through the coil and sends it to the antenna for transmission.
3.2. Using the Tuned Circuit
Here, the FM circuit has a frequency determining stage (tuned circuit) built into its PCB. If you want the best performance from this circuit, use the traditional wound coil type and avoid etched antenna coils.
3.3. Integration of the Q factor
The circuit here uses the “Q factor” to generate high voltages. This power comes from the tank array capacitor and coil. With the Q factor, the circuit has improved performance and can transmit over longer distances.
3.4. Better saturation capacity
A circuit with better saturation capability has a common-emitter design which is different from common base types. It has inductors at its base which give better saturation capability and healthier transistor response.
3.5. Adjustable coil slug
This design uses a slug-based variable inductor which makes it far superior to its other counterparts. You can tune your transmitter by simply adjusting the slug core with a screwdriver. This circuit has the best transmission range, but it is not very stable.
3.6. Improved stability
I mentioned that the adjustable coil slug circuit wasn't stable - luckily you can improve its stability by adjusting the antenna from part of the coil. In addition, it improves the overall performance of the circuit.
3.7. streaming music
If you want music rather than listening to frequencies then this design will intrigue you. With this transmitter, you can combine a stereo input with the source, which allows the electronic audio signal inside the two radio channels to be transmitted satisfactorily. Here is an image of the design.
we are going to show you how to make an FM transmitter using 3 2N2222 transistors. This transmitter will allow you to transmit your voice to a remote location.
This circuit is a great way to transmit sound without having to use wired connections. By
using this circuit, you will be able to transmit your voice without any lag
FM Transmitter Circuits: How To Build One Custom For You
Does your engineering project need an FM Transmitter Circuits, but you have no idea how to make one? Then this article is for you.
The FM transmitter circuit is a crucial part of wireless and Bluetooth communication circuit and carrier frequency projects. Moreover, it is efficient and can be tricky, due to its intricate diagrams and design.
Image showing a frequency modulation (FM) vector diagram
Fortunately, this guide will make your job easier by breaking down the big chunks of information and frustrating diagrams.
Therefore, make us comfortable and immerse ourselves.
1. What is an FM transmitter circuit
FM (Frequency Modulation) transmitter is an electronic circuit that manipulates a carrier signal wave to transmit useful information or data.
Also, it uses a single transmitter and does not require a massive power supply to transmit audio input signals over long or short distances.
For an FM transmitter circuit to work, you need a portable audio device like an MP3 player or a mobile phone.
Therefore, you can connect the transmitter to the headphone jack of your audio device and send sound signals on an FM band frequency.
Any radio station within transmission range can pick up any message signal.
2. How to make an FM transmitter circuit
Image showing an engineer creating an FM transmitter circuit
This section will show you how to create the simplest DIY FM transmitter circuit that works perfectly.
2.1 FM Transmitter Circuit Production Tools
Here are the things you need to make an FM transmitter circuit:
9v battery
variable capacitor
Antenna
Microphone or other audio input
Inductor
Resistors and capacitors
Transistors
2.2 Circuit diagram and description
If you're new to this, the circuit diagrams might look a bit confusing. But, don't worry, we're here to make it easy. Take a look at this handy diagram of a circuit.
This circuit diagram shows an FM transmitter with a 9v supply. Also, the microphone is the input device that receives the sound signals.
Therefore, you can generate sound radio wave signals when you speak into the microphone. Also, the microphone has capacitive plates that create energy from the sounds you make.
Then it varies the audio wave at the splitter junction and transforms it into audio signals. After that, the capacitor (C1) cancels the noise from the audio signal and sends it to the transistor (Q1).
The transistors send the sound signals to the LC tank circuit. Moreover, the circuit is necessary because it generates the motion of fixed frequency.
The audio signal from the transistor will then modulate the fixed frequency signal. Then the modified signal transmits to the antenna, which sends the sound signal to any receiver within 30 meters.
2.3 FM Transmitter Circuit Design
The FM transmitter circuit has different designs ranging from simple to complicated. So, let's look at two basic techniques that are common and easy to create.
2.3.1 Wireless design
The design of the wireless circuit sends signals that transmit through a radio tuned to the corresponding frequency band.
The frequency depends on how the inductor is placed and the values of C1, C2 and C3. Additionally, you can manipulate the distance or coil diameter to effect the perfect response on FM receivers.
A small wire antenna (about 3 inches) can be attached to the point shown to make the bug highly responsive and create distortion-free signals.
So here is the design of the wireless FM transmitter circuit.
2.3.2 Design of a transistor
This design is the simplest transmitter circuit to manufacture. However, its simplicity creates some drawbacks such as:
Small transmission range
It uses a 1.5V battery with limited capabilities
The single transistor design does not use a microphone as a sound input device. Instead, its antenna performs a dual function (it detects and transmits sound vibrations). Also, it has no frequency determining step. Thus, it cannot be called a tuned transmitter circuit.
Therefore, let's look at the cDesigning the parts you need to build an FM transmitter circuit.
2.3.3 Audio preamplifier design
This design depicts a preamplifier with a simple single-stage common-emitter amplifier.
Vdc selection
We chose the NPN bipolar junction transistor, BC109. Also, it has a voltage of around 40V, so we selected a smaller Vcc (9V).
Load resistor, R4
Diagram showing load resistance
Here calculating the quiescent collector current will give you the value of the load resistor. Thus, the collected voltage should be 1/2 of the selected Vcc. Again, this means that the value of our fixed load resistor, R4, is 4.5k. So we chose a 5K load resistor for maximum performance.
Voltage divider resistors R2 and R3
You can get the value of the voltage divider resistors by calculating the voltage across all the resistors and the bias current.
Moreover, the bias current has an approximate value of 10 times the base current. The base current (lb) here is 0.008mA – Therefore our bias current is 0.08mA.
Also, the voltage across the resistors (Vb) is assumed to be 0.7v higher than the emitter voltage (Ve). So, for example, if our Ve is 12% of the Vcc (1.08v), our Vb will be 1.78v.
Therefore, R2 = Vb/lbias = 22.25k. So we chose a 22k resistor.
R3 = (Vcc-Vb/lbias = 90.1k. So we chose a 90k resistor.
Emitter resistor R5
To obtain the value of R5, use the formula Ve/le. Le is the emitter current and has the same value as the collector current. Therefore, R5 = (Ve/le) = 540 Ohms. So we choose a 500 Ohm resistor because it can bypass the emitter current.
Coupling capacitor, C1
The purpose of the capacitor is to modulate the current flows through the transistor. Thus, large values show lower frequencies (bass) while lower values show higher frequencies (treble). Here we choose a value of 5uF for our C1.
Microphone resistor R1
This resistor limits the amount of current flowing through the mic so that it stays below the maximum the mic can handle. Also, if the maximum current value of our mic is 0.4mA, then the value of Rm = (Vcc-Vb)/0.4 = 18.05k. As it should be less, we choose an 18k resistor.
Bypass capacitor, C4
For the C4, we chose an electrolytic capacitor that bypasses the DC signal with a value of 15 uF.
2.3.4 Design of the oscillator circuit
Here is the design of a simple oscillator circuit:
Tank Circuit Components – L1 and C6: We need an oscillation frequency between 88 MHz and 10 MHz for this selection. Thus, we choose a capacitor in the range of 5 to 20pF. Using a 0.2uH inductor will give our C6 an approximate value of 12pF.
Tank Capacitor, C9: This capacitor aims to keep the circuit tanj=k vibrating. So we will choose a 5pF capacitor if our value is between 4 and 10 pF.
R6 and R7 Bias Resistors: Based on the calculations for the bias resistors in the preamplifier design, our R6 and R7 resistors will be 9K and 40K.
Coupling Capacitor, C3: We chose 0.01uF electrolytic capacitors for our coupling capacitor.
Emitter Resistor, R8: The emitter resistor will have an approximate value of 1K, based on previous calculations for the amplifier circuit.
2.3.5 Power Amplifier Circuit Design
FM transmitter circuits do not require high power output, so we chose a class A power amplifier with an LC tank circuit as the output.
Also, our tank circuit has the same values as that of our oscillator circuit. So we choose a bias resistor with a value of 20 K and a coupling factor of 10 pF.
2.3.6 Antenna Selection
The range of our FM transmitter circuit is about 2 km, so we choose a stick antenna that is 1/4th the transmitter wavelength. Other antenna options also include 30 inch wire.
2.4 Detailed steps
Here are four steps to guide you when creating your FM transmitter circuit.
2.4.1 Obtain required components
Make sure you have all the components you need before you start building an FM transmitter circuit.
So for this FM transmitter circuit you will need the 2N3904-2 transistors, five resistors: 100k Ω-1, 100Ω-1, 1M Ω-1, 1k Ω-1 and 10k Ω-3, a 0.1uH inductor , four capacitors: 0.1 pF – 2, trimmer 40 pF – 1, 4.7 pF – 1, 10pF -1, an antenna, a bNext, make your inductor out of 18 or 22 gauge copper wire. If using the 18 gauge copper wire, create a 4 to 5 turn inductor with 1/4 inch (oR). For 22 gauge, create an 8-10 inductor with 1/4 inch.
After creating your inductor, be sure to solder it to the circuit.
Solder your antenna to the circuit. So you can select 8-10cm patch wire as antenna or use standard antenna.
2.4.4 Transmitter Setup
Transmitter tuning is tricky and the process takes some time, so it requires patience and caution.
When you vary the trimmer capacitor, you can adjust the transmission frequency.
So slowly vary the capacity of the trimmer until you hear distortion. Then slowly tune into the distortion area until your transmitter matches the radio frequency. Then you will hear a clear output from the radio.
Once the tuning is complete, you will have a completed FM transmitter circuit.
3. FM transmitter circuits with its special functions
Here are some special functions of the FM transmitter circuit:
3.1. Circuit operation
When you turn on the FM circuit, the capacitor keeps the transistor from changing until it is charged.
Once the 22n capacitor is discharged, it turns off the transistors until it recharges – this procedure quickly generates a frequency through the coil and sends it to the antenna for transmission.
3.2. Using the Tuned Circuit
Here, the FM circuit has a frequency determining stage (tuned circuit) built into its PCB. If you want the best performance from this circuit, use the traditional wound coil type and avoid etched antenna coils.
3.3. Integration of the Q factor
The circuit here uses the “Q factor” to generate high voltages. This power comes from the tank array capacitor and coil. With the Q factor, the circuit has improved performance and can transmit over longer distances.
3.4. Better saturation capacity
A circuit with better saturation capability has a common-emitter design which is different from common base types. It has inductors at its base which give better saturation capability and healthier transistor response.
3.5. Adjustable coil slug
This design uses a slug-based variable inductor which makes it far superior to its other counterparts. You can tune your transmitter by simply adjusting the slug core with a screwdriver. This circuit has the best transmission range, but it is not very stable.
3.6. Improved stability
I mentioned that the adjustable coil slug circuit wasn't stable - luckily you can improve its stability by adjusting the antenna from part of the coil. In addition, it improves the overall performance of the circuit.
3.7. streaming music
If you want music rather than listening to frequencies then this design will intrigue you. With this transmitter, you can combine a stereo input with the source, which allows the electronic audio signal inside the two radio channels to be transmitted satisfactorily. Here is an image of the design.
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