COMSATS Institute of Information Technology

Project:
F.M. WIRELESS MIC
(Electronics - 1)

Presented to - Mam Samia Aslam Made by - Waqas Hassan (CIIT/SP09-BPH-016/LHR)

Zubair Bhutta (CIIT/SP09-BPH-009/LHR) Noor Elahi (CIIT/SP09-BPH-011/LHR)

Circuit Diagram:

Components: 1. Mic 2. Resistors - 10k (2) - 47k (2) 3. Variable Resistor - 8pF 4. Transistors - C945 - C2120 5. Capacitors - 4.7F - 203 (2) - 5.6pF 6. Battery 9V 7. Antenna

MIC:
Definition:
A microphone (called a mic or mike) that converts sound waves into an electrical variations which may then amplified, transmitted or recorded.

Working:
1. 2. 3. 4. Sound waves carry energy toward the microphone. The diaphragm moves back and forth when sound waves hit it. The coil, attached to the diaphragm, moves back and forth as well. The permanent magnet produces a magnetic field that cuts through the coil. As the coil moves back and forth through the magnetic field, an electric current flows through it. 5. The electric current flows out from the microphone to an amplifier or sound recording device.

RESISTORS:
Definition:
Resistor is device having resistance to the passage of an electric current.

Working:
In electronics we use a resistor when we need to reduce the voltage applied to a circuit. A resistor is defined by several parameters: Resistance in Ohms () Heat Dissipation in Watts (W) Manufacturing tolerance (%)

Variable Resistor:
Definition:
A potentiometer (known as a "pot") is a three-terminal resistor with a sliding contact that forms an adjustable voltage divider. If only two terminals are used (one side and the wiper), it acts as a variable resistor or rheostat.

Working:
A variable resistor is a strip of a material such as graphite which resists the flow of electricity. There is a fixed terminal attached to one end of the resistor. There is also a moving device touching the graphite called a wiper. When the resistor is adjusted, the wiper slides along the graphite, either towards or away from the terminal. When the wiper is close to the terminal, the electricity only has to flow through a little bit of the resistive material and the resistance is fairly low. When the wiper is further away, the electricity has to travel much further through it, and the resistance is much higher.

Transistors:
Definition:
Transistor a semiconductor device with three connections, capable of amplification and rectification.

Working:
The design of a transistor allows it to function as an amplifier or a switch. Transistors are composed of three parts a base, a collector, and an emitter. The base is the gate controller device for the larger electrical supply. The collector is the larger electrical supply, and the emitter is the outlet for that supply. By sending varying levels of current from the base, the amount of current flowing through the gate from the collector may be regulated. In this way, a very small amount of current may be used to control a large amount of current, as in an amplifier.

Capacitors:
Definition:
A capacitor is a device used to store a charge, consisting of one or more pair of conductors separated by a dielectric (insulator).

Working:
In a way, a capacitor is a little like a battery. Although they work in completely different ways, capacitors and batteries both store electrical energy. If you have read How Batteries Work, then you know that a battery has two terminals. Inside the battery, chemical reactions produce electrons on one terminal and absorb electrons on the other terminal. A capacitor is much simpler than a battery, as it can't produce new electrons -- it only stores them.

Battery:
Definition:
A container consisting of one or more cells, in which chemical energy converted into electricity and used as a source of power.

Working:
It consists of a number of voltaic cells; each voltaic cell consists of two half cells connected in series by a conductive electrolyte containing anions and cations. One half-cell includes electrolyte and the electrode to which anions (negatively-charged ions) migrate, i.e., the anode or negative electrode; the other half-cell includes electrolyte and the electrode to which cations (positively-charged ions) migrate, i.e., the cathode or positive electrode. In the redox reaction that powers the battery, reduction (addition of electrons) occurs to cations at the cathode, while oxidation (removal of electrons) occurs to anions at the anode. The electrodes do not touch each other but are electrically connected by the electrolyte. Many cells use two half-cells with

different electrolytes. In that case each half-cell is enclosed in a container, and a separator that is porous to ions but not the bulk of the electrolytes prevents mixing.

Antenna:
Definition:
Antenna (radio), also known as an aerial, a transducer designed to transmit or receive electromagnetic (e.g. TV or radio) waves.

Working:
Antennas work in the same way. When electricity is "thrown" into the metal of an antenna, the metal reacts to the electricity at an atomic level in the form of a wave. This wave, just like the beach ball wave in the swimming pool, radiates outward from the point where the electricity enters the antenna. Now, because antennas are working with radio waves and not water waves, the waves in the metal of the antenna actually produce waves in the air touching the antenna. The waves also continue outward through the air until they encounter interference which is why you will have difficulty receiving a radio signal deep inside a building. The structure of the building

is stopping the radio waves in the air from getting to you, just like the edge of the pool prevents the water waves from getting to you as you sit in your pool side lounger.

General Working:
This is a small but quite powerful FM transmitter. It is the ideal project for the beginner who wishes to get started in the fascinating world of FM broadcasting and wants a good basic circuit to experiment with. The output frequency the transmitter is adjustable from 88 to 108 MHz which is the FM band that is used for radio broadcasting. The electric microphone has a resistance that depends on how loudly you speak into it. This microphone is battery powered and according to the V=IR Ohm's Law, changes in resistance for fixed voltage will result in proportional changes in current. This current feeds into the base of the c2120, c945 NPN transistor which is connected to your variable capacitor, inductor and antenna. The net effect is that depending on your variable capacitor's value, your voice will be modulated to transmit at a frequency between 88 and 108 MHz If a nearby pocket FM radio is tuned to this frequency, you'll be heard when speaking into your transmitter.