Making a simple FM Transmitter

FM Transmitters are that type of gadget which gives you the feelings of a RJ. You can make your own short-range radio channel and air any songs, audio clips as well as your voice in the form of radio frequency. The transmission process is done by following steps which are audio pre amplification followed by modulation then transmission. There are two types of modulation Amplitude Modulation(AM) & Frequency Modulation(FM) both are the part of Radio Frequency (RF). 88 MHz to 180 MHz is generally known as the FM Band.

Audio signal from media player, microphones are very low level signal, of the order of mill volts. This extremely small voltage needs to be first amplified. A common emitter configuration of a bipolar transistor produces an amplified inverted signal.

Another important aspect of this circuit is the oscillator circuit. This is a LC oscillator where energy moves back and forth between the inductor and capacitor forming oscillations. It is mainly used for RF application.

When this oscillator is given a voltage input, the output signal is a mixture of the input signal and the oscillating output signal, producing a modulated signal. In other words, the frequency of the oscillator generated circuit varies with the application of an input signal, producing a frequency modulated signal.

transmitter
A simple Fm Transmitter Circuit

Some details about the design of the circuit :

1.Selecting the Vcc : This circuit uses a NPN Bipolar Junction Transistor (2N3904) or you can use BC547 or equivalent. The Vceo of the transistor is 40V so minimum Vcc is 9V.

2.Selecting the Capacitor C1 : The capacitor modulates the current going through the transistor. A large value indicates bass or low frequency whereas small value indicates treble higher frequency. Here 1uF, 25V electrolytic capacitor is used.

3.Selecting L1 & C4 : Here L1 & C4 is the oscillator known as LC oscillator. Frequency of oscillation is obtained from the formula, f = 1/(2Π√LC). 

Here is some pictures of my complete and decorated setup :

breadboard setup
Breadboard setup
decorated setup1
Decorated setup1
setup2
Complete setup

 

 

 

 

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Hacking the Switched Mode Power Supply

Hacking & something more on the SMPS

The SMPS or the Switched Mode power Supply generally used to drive our Personal Computers. It can also be used to drive other loads also so it is a versatile power supply.

Why SMPS is used in Personal Computers?

In the motherboard of a Personal Computer different sections needs different operating voltages those are +3.3V, +5V, -5V, +12V, -12V DC. The SMPS converts & switches 230V AC supply to those voltages respectively in a very short time so it minimizes the wastage of energy thus the efficiency increases. An ideal SMPS dissipates no power.
introduction
Stages of AC to DC conversion & Switching done in a SMPS:
 
Stages of conversion

Hacking the SMPS & using it as your own power supply

Using the Switched Mode Power Supply as a workbench power supply is not so difficult. Everyone can use it. Starting from beginner level, if you Plug in the SMPS and you will find it is not running. Well that not means that the device is damaged.

Running the SMPS

Step 1: Go for the ATX Power connector. It is the connector having 20 or 24 pins. 
ATX Power connector
Step 2: There is only a green wire(PS_ON). Now short PS_ON with any of the Black wire(COM/Ground) of the SMPS and Plug it again to AC. Now if the SMPS is working the fan will start rotating. Now you are able to use it as your power supply.
 
There is only one green wire(PS_ON) short it with and of the black wire(COM/Ground)
ATX Pin out
Step 3: Now check the voltages of the different pins using a multimeter. 
Reading 1
Reading 2
Reading 3
Step 4: Now use the SMPS as a power supply. I’ve use an old one as my workbench power supply. Here is a simple LED test circuit.
 
Test Circuit