July 03, 2013

50 Watts Inverter Circuit

A 50 watt inverter might look quite trivial, but it can serve some useful purposes to you. When outdoors, this small power house can be used for operating small electronic gadgets, soldering iron, table top radios, incandescent lights, fans etc.
Let’s learn how to build this homemade 50 watt inverter unit, beginning with a brief description regarding the circuit diagram and its functioning:

Circuit Description

The circuit may be understood with the following points:
Referring to the figure, transistors T1 and T2 along with the other R1, R2, R3 R4, C1 and C2 together form a simple astable multivibrator (AMV) circuit. A multivibrator circuit basically is composed of two symmetrical half stages, here its formed by the left and the right hand side transistor stages which conduct in tandem or in simple words the left and the right stages conduct alternately in a kind of a perpetual “motion”, generating a continuous flip flop action.
The above action is responsible of creating the required oscillations for our inverter circuit. The frequency of the oscillation is directly proportional to the values of the capacitors or/and the resistors at the base of each transistor.
Lowering the values of the capacitors increases the frequency while increasing the values of the resistors decreases the frequency and vice versa. Here the values are chosen so as to produce a stable frequency of 50 Hz.
Readers, who wish to alter the frequency to 60 Hz, may easily do it by just changing the capacitor values appropriately.
Transistors T2 and T3 are placed at the two output arms of the AMV circuit. These are high gain; high current Darlington paired transistors, used as the output devices for the present configuration.
The frequency from the AMV is fed to the base of T2 and T3 alternately which in turn switch the transformer secondary winding, dumping the entire battery power in the transformer winding.
This results in a fast magnetic induction switching across the transformer windings, resulting the required the mains voltage at the output of the transformer.

Parts Required

You will require the following components for making this 50 watt homemade inverter circuit:
R1, R2 = 100K,
R3, R4 = 330 Ohms,
R5, R6 = 470 Ohms, 2 Watt,
R7, R8 = 22 Ohms, 5 Watt
C1, C2 = 0.22 uF, Ceramic Disc,
D1, D2 = 1N5402 or 1N5408
T1, T2 = 8050,
T3, T4 = BC316,
T5, T6 = 2N3055 (TO-220)
General purpose PCB = cut into the desired size, approximately 5 by 4 inches should suffice.
Battery: 12 volts, Current not less than 10 AH.
Transformer = 9 – 0 – 9 volts, 5 Amps, Output winding may be 220 V or 120 volts as per your country specifications
Sundries: Metallic box, fuse holder, connecting cords, sockets etc
Testing and Setting Up the Circuit

After you finish making the above explained inverter circuit, you may do the testing of the unit in the following manner:
Initially do not connect the transformer or battery to the circuit.
Using a small DC power supply power the circuit.
If everything is done rightly, the circuit should start oscillating at the rated frequency of 50 Hz.
You can check this by connecting the prods of a frequency meter across T3’s or T4’s collector and the ground. The positive of the prod should go to the collector of the transistor.
If you don’t own a frequency meter, never mind, you do a rough checking by connecting a headphone pin across the above explained terminals of the circuit. If you hear a loud humming sound, will prove that your circuit is generating the required frequency output.
Now it’s time to integrate the battery and the transformer to the above circuit.
Connect everything as shown in the figure.
Connect a 40 watt incandescent lamp  at the output of the transformer. And switch ON the battery to the circuit.

The bulb will immediately come ON brightly…..your homemade 50 watt inverrer is ready and may be used as desired by for powering many small appliances whenever required.

November 25, 2011

Working of Camera

The work of a camera – photography is considered to be one of the greatest inventions of mankind. It has not only helped us see the entire world through a click, but has also transformed how people conceive the world. They can also be kept as a remembrance for the rest of our life.
Camera can be defined as a device that is used to capture and record photos or videos.

After years of work by many prominent people the first colour photo was invented by the famous physicist James Clark Maxwell along with Thomas Sutton. Then came the invention of the video made in cameras during the early 1920s. This technology has eventually grown to such heights that in this 21st century, these ordinary film cameras have been replaced by digital cameras.

Parts of a camera

A camera has mainly three parts. They are
  • Mechanical part or the camera body
  • Optical part or the lens section
  • The chemical part or the film
The way in which these three parts are connected represents the different types of cameras. Thus by combining these three parts and using them under the correct calibration produces a correct picture. They are capable of working in both the visible spectrum as well as in other portions of the electromagnetic spectrum. The basic shape of a camera needs an enclosed hollow chamber with an opening at one end. This opening, also called aperture helps in the entrance of light. This light is the actual image that has to be captured. So a capturing mechanism is set at the other end. All cameras have the lens assembled in the front. This lens helps in capturing the light, which is in turn captured and stored by the recording surface. Most ordinary cameras can take one image at a time. Most video cameras can take a maximum of 24 film frames/sec.

Mechanism of a camera

To know the complete mechanism of the camera, it is better to know each and every parameter of the camera.

1. Focus
A camera’s focus greatly depends on the clarity of the picture taken. But the focus can be limited only to a certain distance. This range is limited to the range of the lens. This range when adjusted to get a perfect image is called the focus of the camera. For accurate focussing of cameras, the device is comprised of a fixed focus and also consists of a wide-angle lens and a small aperture in front of the camera. The range of focus will be clearly indicated in the camera with symbols like two people standing upright, mountains and so on. For a simple camera, a reasonable focus of about 3 meters to infinity is available. The focus available on each camera is different. Single-lens reflex (SLR) cameras have a focus that can be changed according to our like. This is done by providing a objective lens and a moving mirror so as to projecting the image to a ground glass or plastic micro-prism screen. Similarly each camera has different settings which will be explained briefly later.
  • The focus of a camera depends on two main features. They are
  • The structure and position of the lens.
  • The angle in which the light beams enter into the lens.
Consider a pencil kept at a short distance from the lens. When the distance is altered, that is kept near and then farther away from the lens, the angle of entry of the light changes accordingly. This light is hit on the film surface kept inside the camera. The angle becomes sharper when the image is close to the lens and will become narrower when the image is kept far away. Thus when the lens is focused farther and then nearer from the pencil, the image is actually moving closer or farther away from the film surface. The correct image will be obtained when the focus is adjusted in such a way that you can line up the focused real image of an object so it falls directly on the film surface.

2. Camera Lens

The quality of the photograph taken largely depends on the type of lens used. The precision of a lens depends on a factor called “bending angle”. This in turn, depends on the structure of the lens. If the lens has a flat shape, the bending angle is less. Thus the light beams will converge a little distance farther away from the lens. Thus the image is also formed farther away. Thus when the distance increases, the size of the image also increases, though the size of the film is constant. If the lens has a round shape, the bending angle will be high. Thus the image will be formed a lot more nearer to the lens.
Costly cameras have a lot of lenses, which are replaced or combined according to the magnification required. This magnification power of a lens is called the focal length. Greater the focal length, greater the magnification.

3. Camera Film

For an image to be recorded and viewed it must be stored in a film. When an image is captured, it is actually being “chemically” recorded onto a film. The film mainly consists of millions of light-sensitive grains, which are suspended on a plastic strip. These grains chemically react, when exposed to light. This reaction causes the image to be recorded on the film. This film is then developed by reacting it with other chemicals. For black and white films, the chemicals cause the grains to appear darker when exposed to light. Thus, the darker areas appear lighter and the lighter areas appear darker. This is reversed while printing out the photos.
For producing colour films, the film consists of light sensitive materials that respond to colours red, green and blue. When they are washed and chemically reacted, you get a negative of a colour photo.

Different camera designs

There are a lot of types of cameras like Plate camera, large format camera, medium format camera, folding camera, rangefinder camera and so on. Out of these the most used ones are the single-lens reflex camera (SLR) and the point and shoot camera. The difference comes in the manner in which the photographer visualizes the scene. In a point and shoot camera, you do not see the real image through the camera lens. Instead, you get to see only a blurred vision of the image.
In an SLR camera, you can see the real image of the scee you are about to capture. It has the same configuration as that of a periscope. When the image is seen from the lens, it hits the lower mirror and bounces from there. It then hits the prism. This prism flips the image to form the original image. The mirror and translucent screen help in providing the exact image to the photographer. Thus, you can focus and compose the image so as to get the exact picture you have in mind.
SLR Camera
SLR Camera
With upcoming technology, the point and shoot cameras are nowadays fully automatic. SLR is built with both manual and automatic controls. The only difference between the manual and automatic cameras is that the former will be controlled by a central processor, instead of the photographer.
The focus system and the light meter transmit the signals to the microprocessor and thus activate all the motors accordingly. These motors control the adjusting lens and also open and close the aperture.

Metal Detector

It's a simple metal detector design that has the quite good characteristics. the principle of operation which one differs from the classic schemes (BFO, transmit-receive known as "two-boxes" metal detector, inductive).

The dynamic mode is used to find targets in interference environment. There is known from theory of signal filtration that if signal shape is determined we can construct optimal filter - the best one for extracting the signal with maximum signal/noise ratio. This filter is known as optimal matched filter. In our device we realized digital optimal matched filter as part of microcontroller software. The filter parameters are optimized for effective ferro- and non-ferro targets detection on 0.5-1.0 m/s velocity of sensor.

Features of the Metal Detector:
Power supply .............................4.5-6V;
DC consumption .......................15 mA;
Indication ...................................sound + 8 LEDs;
Modes ........................................static or dynamic;

Metal Detector Schematic

Switches controlled (versions V1.9 and V2.0 of firmware):
S0: reset device;
S1: reserved;
S2: on - threshold high, off - threshold low;
S3: measuring time on - 30ms, off - 120ms;
S4: self tuning on/off (in dynamic mode only);
S5: mode on - static, off - dynamic.

Metal detector PCB Layout

Metal Detector Coil Design

Approx. 100 curls 200 mm in diameter. Copper wire in isolation 0,35 mm diameter


Mobile phone call indicator

This circuit can be used to escape from the nuisance of mobile phone rings when you are at home. This circuit will give a visual indication if placed near a mobile phone even if the ringer is deactivated. This circuit was designed to detect when a call is incoming in a cellular phone (even when the calling tone of the device is switched-off) by means of a flashing LED.

The device must be placed a few centimeters from the cellular phone, so its sensor coil L1 can detect the field emitted by the phone receiver during an incoming call.

Device operation

When a call is coming to the mobile phone, the transmitter inside it becomes activated. The  frequency of the transmitter is around 900MHz.The  coil L1 picks up these oscillations by induction and feds it to the base of Q1. This makes the transistor Q1 activated.Since the Collector of Q1 is connected to the pin 2 of IC1 (NE555) , the IC1 is triggered to make the LED connected at  its output pin (pin 3) to blink. The blinking of the LED is the indication of incoming call.

The signal detected by the sensor coil is amplified by transistor Q1 and drives the monostable input pin of IC1. The IC's output voltage is doubled by C2 & D2 in order to drive the high-efficiency ultra-bright LED at a suitable peak-voltage.


  • Stand-by current drawing is less than 200µA, therefore a power on/off switch is unnecessary.
  • Sensitivity of this circuit depends on the sensor coil type.
  • L1 can be made by winding 130 to 150 turns of 0.2 mm. enameled wire on a 5 cm. diameter former (e.g. a can). Remove the coil from the former and wind it with insulating tape, thus obtaining a stand-alone coil.
  • A commercial 10mH miniature inductor, usually sold in the form of a tiny rectangular plastic box, can be used satisfactorily but with lower sensitivity.
  • IC1 must be a CMos type: only these devices can safely operate at 1.5V supply or less.
  • Any Schottky-barrier type diode can be used in place of the 1N5819: the BAT46 type is a very good choice.

November 19, 2011


SOLAR CELLS, How They Work


The solar cell offers a limitless and environmentally friendly source of electricity. The solar cell, is able to create electricity directly from photons. A photon can be thought of as a packet of light and the amount of energy in a photon is proportional to the wavelength of light.


Solar Cell Structure:


A. Encapsulate - The encapsulate, made of glass or other clear material such clear plastic, seals the cell from the external environment.
B. Contact Grid- The contact grid is made of a good conductor, such as a metal, and it serves as a collector of electrons.
C. The Anti reflective Coating (AR Coating)- Through a combination of a favorable refractive index, and thickness, this layer serves to guide light into the solar cell. Without this layer, much of the light would simply bounce off the surface.
D. N-Type Silicon - N-type silicon is created by doping (contaminating) the Si with compounds that contain one more valence electrons* than Si does, such as with either Phosphorus or Arsenic. Since only four electrons are required to bond with the four adjacent silicon atoms, the fifth valence electron is available for conduction.
E. P-Type Silicon- P-type silicon is created by doping with compounds containing one less valence electrons* than Si does, such as with Boron. When silicon (four valence electrons) is doped with atoms that have one less valence electrons (three valence electrons), only three electrons are available for bonding with four adjacent silicon atoms, therefore an incomplete bond (hole) exists which can attract an electron from a nearby atom. Filling one hole creates another hole in a different Si atom. This movement of holes is available for conduction.
F. Back Contact - The back contact, made out of a metal, covers the entire back surface of the solar cell and acts as a conductor.
*[ A valence electron is an electron found in the outermost electron shell. An element containing more valence electrons will try to donate valence electrons to an element containing fewer valence electrons.] *

A photon's  path through the solar cell

Once the photon passes the anti reflective layer, it will either hit the silicon surface of the solar cell or the contact grid metallization. The metallization, being opaque, lowers the number of photons reaching the Si surface. The contact grid must be large enough to collect electrons yet cover as little of the solar cell's surface, allowing more photons to penetrate.

A Photon causes the Photoelectric Effect*.

The photon's energy transfers to the valence electron of an atom in the n-type Si layer. That energy allows the valence electron to escape its orbit leaving behind a hole. In the n-type silicon layer, the free electrons are called majority carriers whereas the holes are called minority carriers. As the term "carrier" implies, both are able to move throughout the silicon layer of the solar cell, and so are said to be mobile. Inversely, in the p-type silicon layer, electrons are termed minority carriers and holes are termed majority carriers, and of course are also mobile.
*[ The photoelectric effect is simply defined as an experimentally measurable effect where a metal emits electrons when hit by photons..] *

The p-n junction.

The region in the solar cell where the n-type and p-type Si layers meet is called the p-n junction. As you may have already guessed, the p-type silicon layer contains more positive charges, called holes, and the n-type silicon layer contains more negative charges, or electrons. When p-type and n-type materials are placed in contact with each other, current will flow readily in one direction (forward biased) but not in the other (reverse biased).

An interesting interaction occurs at the p-n junction of a darkened solar cell. Extra valence electrons in the n-type layer move into the p-type layer filling the holes in the p-type layer forming what is called a depletion zone. The depletion zone does not contain any mobile positive or negative charges. Moreover, this zone keeps other charges from the p and n-type layers from moving across it.

So, to recap, a region depleted of carriers is left around the junction, and a small electrical imbalance exists inside the solar cell. This electrical imbalance amounts to about 0.6 to 0.7 volts. So due to the p-n junction, a built in electric field is always present across the solar cell.

P = V × I

When photons hit the solar cell, freed electrons (-) attempt to unite with holes on the p-type layer. The p-n junction, a one-way road, only allows the electrons to move in one direction. If we provide an external conductive path, electrons will flow through this path to their original (p-type) side to unite with holes.

The electron flow provides the current ( I ), and the cell's electric field causes a voltage ( V ). With both current and voltage, we have power ( P ), which is just the product of the two. Therefore, when an external load (such as an electric bulb) is connected between the front and back contacts, electricity flows in the cell, working for us along the way.


Electronics is the study and use of electrical that operate by controlling the flow of electrons or other electrically charged particles in devices such as thermionic valves. and semiconductors. The pure study of such devices is considered as a branch of physics, while the design and construction electronic circuits to solve practical problems is called electronic engineering.

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