10-04-2010, 09:11 PM
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LASER TORCH BASED VOICE TRANSMITTER AND RECEIVER
Using this circuit you can communicate with your neighbors wirelessly. Instead of RF signals, light from a laser torch is used as the carrier in the circuit. The laser torch can transmit light up to a distance of about 500 meters. The phototransistor of the receiver must be accurately oriented towards the laser beam from the torch. If there is any obstruction in the path of the laser beam, no sound will be heard from the receiver. The transmitter circuit (Fig. 1) comprises condenser microphone transistor amplifier BC548 (T1) followed by an pomp stage built around µA741 (IC1). The gain of the op-amp can be controlled with the help of 1-mega-ohm potmeter VR1.The AF output from IC1 is coupled to the base of transistor BD139 (T2), which, in
turn, modulates the laser beam.
The transmitter uses 9V power supply. However, the 3-volt laser torch (after removal of its battery) can be directly connected to the circuitâ€with the body of
The torch connected to the emitter ofBD139 and the spring-loaded lead protruding from inside the torch to circuit ground. The receiver circuit (Fig. 2) uses an npn phototransistor as the light sensor that is followed by a two-stage transistor preamplifier and LM386-based audio
Power amplifier. The receiver does not need any complicated alignment. Just keep
the phototransistor oriented towards the remote transmitterâ„¢s laser point and adjust
The volume control for a clear sound. To avoid 50Hz hum noise in the speaker, keep the phototransistor away from AC light sources such as bulbs. The reflected sunlight, however, does not cause any problem. But the sensor should not directly face the sun.
A BRIEF SUMMARY OF COMPONENTS USED
When a beginner to electronics first looks at a circuit board full of components
he/she is often overwhelmed by the diversity of do-dads. In these next few sections we will help you to identify some of the simple components and their schematical symbol. Then you should be able to call them resistors and transistors instead of Whatchamacallits.
Electronic component are classed into either being Passive devices
Or Active devices.
A Passive Device is one that contributes no power gain (amplification)
to a circuit or system. It has not control action and does not require any
input other than a signal to perform its function. In other words, A
components with no brains! Examples are Resistors, Capactitors and
Inductors
Active Devices are components that are capable of controlling voltages
or currents and can create a switching action in the circuit. In other
words, Devices with smarts! Examples are Diodes, Transistors and
Integrated circuits. Most active components are semiconductors.
Resistors:
This is the most common component in electronics. It is used mainly to control
current and voltage within the circuit. You can identify a simple resistor
by its simple cigar shape with a wire lead coming out of each end. It uses a
system of color coded bands to identify the value of the component (measured
in Ohms) *A surface mount resistor is in fact mere millimeters in size
but performs the same function as its bigger brother, the simple resistor. A
potentiometer is a variable resistor. It lets you vary the resistance with a dial
or sliding control in order to alter current or voltage on the fly. This is opposed
to the fixed simple resistors.
Condensers/Capacitors:
Capacitors, or "caps", vary in size and shape - from a small surface mount
model up to a huge electric motor cap the size of a paint can. It storages electrical
energy in the form of electrostatic charge. The size of a capacitor generally determines
how much charge it can store. A small surface mount or ceramic cap will
only hold a minuscule charge. A cylindrical electrolytic cap will store a much
larger charge. Some of the large electrolytic caps can store enough charge to kill
a person. Another type, called Tantalum Capacitors, store a larger charge in a
smaller package.
Inductors:
You may remember from science class that adding electrical current to a coil of
wire produces a magnetic field around itself. This is how the inductor works. It is
charged with a magnetic field and when that field collapses it produces current in
the opposite direction. Inductors are used in Alternating Current circuits to
oppose changes in the existing current. Most inductors can be identified by the
"coil" appearance. Others actually look like a resistor but are usually green in
color.
Diodes:
Diodes are basically a one-way valve for electrical current. They let it flow in one
direction (from positive to negative) and not in the other direction. This is used to perform rectification or conversion of AC current to DC by clipping off the negative portion of a AC waveform. The diode terminals are cathode and anode and the arrow inside the diode symbol points towards the cathode, indicating current flow in that direction when the diode is forward biased and conducting current. Most diodes are similar in appearance to a resistor and will have a painted line on one end showing the direction or flow(white side is negative). If the negative side
is on the negative end of the circuit, current will flow. If the negative is on the positive side of the circuit no current will flow.
LEDs (Light Emitting Diodes)
LEDs are simply diodes that emit light of one form or another. They are used as
indicator devices. Example: LED lit equals machine on. The general purpose silicon
diode emits excess energy in the form of heat when conducting current. If a different
semiconductor material such as gallium, arsenide phosphide is used, the excess
energy can be released at a lower wavelength visible to human eye. This is the
composition of LED. They come in several sizes and colors. Some even emit Infrared
Light which cannot be seen by the human eye.
Switch :
This is a mechanical part which when pressed makes the current to flow through
it. If the switch is released the current stops flowing through it. This helps to control a
circuit.
Transistors:
The transistor performs two basic functions:
1) It acts as a switch turning current on and off.
2) It acts as a amplifier.This makes an output signal that is amagnified version of the input signal.Transistors come in several sizes dependingon their application. It can be a
big power transistor such as is used in power applifiers in your stereo, down to
a surface mount (SMT) and even down to .5 microns wide (I.E.: Mucho Small!)
such as in a microprocessor or IntegratedCircuit.
NPN Transistor: Bipolar junction perform the function of amplifications where
a small varying voltage or current applied to the base (the lead on the left
side of the symbol) is proportionately replicated by a much larger voltage or
current between the collector and emitter leads. Bipolar junction refers to sandwich
construction of the semiconductor, where a wedge of "P" material is placed
between two wedges of "N" material. In this NPN construction a small base current
controls the larger current flowing from collector to emitter (the lead withthe arrow).
PNP Transistor: Similar to NPN transistors, PNP's have a wedge of "N" material
between two wedges of "P" material. In this design, a base current
regulates the larger current flowing from emitter to collector, as indicated
by the direction of the arrow on the emitter lead. In CED players, PNP transistors
are used less frequently that the NPN type for amplification functions.
PCBâ„¢s:
PCB stands for printed circuit board which are used for wiring up of the components of a circuit. PCBs are made of paper phenolic FR2 grade (low cost, for low frequency and low power circuit assembly) and glass epoxy FR4 grade (for high frequency, high power circuits) copper clad laminates (available in 1.6mm, 2.4mm and 3.6mm thickness). Singlesided PCBs have copper foil only on one side while double-sided PCBs have copper foil on both side of the laminate. Thickness of copper foil is 35 micrometer minimum on cheaper PCBs and 70 micrometer on slightly costlier PCBs. Tracks (conductive paths) are made by masking (covering) the track part of copper
with etch-resist enamel paint (you can even use nail polish) and later dipping the
laminate in ferric chloride solutions to dissolve all copper except under the masked
part. Holes in PCBs are drilled after etching is over. The tracks on two sides of a PCB are joined using printed through hole (PTH) technique, which is equivalent to using slotted copper rivets for joining tracks on both sides. On cheaper PCBs, PTH are not provided, only Pads (i.e. circular copper land with centre hole) are provided and you have to join the tracks on both sides by soldering a copper wire to the pads with a copper wire. In singlesided PCB components are mounted on the side which has no track (called component side). In a double-sided PCB the component side is defined (marked before hand) or it will show component outline (also called silk screen)
Green masking is the process of applying a layer of green colour insulation varnish on all parts of tracks except near the holes, to protect the tracks from exposure to atmosphere and thus prolong its life and reliability.
Batteries:
Symbol of batteries shows +ve terminal by a longer line than the “ve terminal.
For low power circuit dry batteries are used.
Speakers:
These convert electrical signals to accoustic viberations. It comprises a permanent
magnet and a moving coil (through which electrical signal is passed). This moving coil is fixed to the diaphram which vibrates to produce sound.
ICs (Integrated Circuits):
Integrated Circuits, or ICs, are complex circuits inside one simple package. Silicon
and metals are used to simulate resistors, capacitors, transistors, etc. It is a space
saving miracle. These components come in a wide variety of packages and sizes.
You can tell them by their "monolithic shape" that has a ton of "pins" coming out
of them. Their applications are as varied as their packages. It can be a simple timer, to
a complex logic circuit, or even a microcontroller (microprocessor with a few added functions) with erasable memory built inside.
Microprocessors (MPUs):
Microprocessors and other large scale ICs are very complex ICs. At their core
is the transistor which provides the logic for computers, cars, TVs and just about
everything else electronic. Packages are becoming smaller and smaller as companies
are learning new tricks to make the transistors ever tinier.
