FM TRANSMITTER

               FM Transmission is a common method in wireless communication which sends the low frequency  audio message in FM range (88 to 108 MHz). The transmitted message can be easily demodulated or decoded by the help of an FM radio receiver.
             The main components required are

• 0.1uH Inductor
  

 Can be easily made by 6-7 turns of 26 SWG (0.45mm) winding wire

• BC547 Transistor
  
• 0-100pF Trimmer Capacitor 
  
• Ceramic Disk Capacitors (22pF,0.001uF)
• Resistors 
• Audio input or Condenser Microphone 
  
• Breadboard or PCB
  

CIRCUIT DIAGRAM 

                     Modulation is the process of superimposing a low energy low frequency signal into a high energy and high frequency carrier signal with changing of any of its properties like frequency, Amplitude or Phase. In the case of FM the frequency of the carrier is varied with the amplitude of message signal .

                    In the above circuit, the Inductor and trimmer capacitor constitutes a tank circuit which generates the carrier frequency. By adjusting the trimmer the frequency of oscillation can be varied.The transmitted signal from the FM transmitter is received and tuned by the FM receiver.

                

SIMPLE CELLPHONE CHARGING CIRCUIT

             A simple mobile phone charging circuit can be constructed from basic components. Here a zener diode and a transistor are the key components of this project. It is NOT suitable for daily purpose usage, but can be used to charge old cellphones. I'am explaining this circuit to only understand the basic working principle only. The main components required are,

• BC 547 Transistor
  
• 4.7 V Zener diode
  
• 100uF Electrolytic Capacitor
• 470 Ω resistor
• Breadboard or PCB

CIRCUIT DIAGRAM

                The above figure is a series voltage regulator. The transistor is used as a control element and the zener used as a dtector. When the input supply voltage Vin increases the output voltage Vload also increases. This increase in Vload will cause a reduced voltage of the transistor base emitter voltage Vbe as the zener voltage Vzener is constant. This reduction in Vbe causes a decrease in the level of conduction which will further increase the collector-emitter resistance of the transistor and thus causing an increase in the transistor collector-emitter voltage and all of this causes the output voltage Vout to reduce. Thus, the output voltage remains constant.