PCB Designing includes the following steps
The entire circuit can be easily assembled on a general purpose P.C.B. board respectively. Layout of desired diagram and preparation is first and most important operation in any printed circuit board manufacturing process. First of all layout of component side is to be made in accordance with available components dimensions.
The following points are to be observed while forming the layout of P.C.B.
Between two components, sufficient space should be maintained.
High voltage/max dissipated components should be mounted at sufficient distance from semiconductor and electrolytic capacitors.
The most important points are that the components layout is making proper compromise with copper side circuit layout.
; ; ; Printed circuit board (P.C.B.s) is used to avoid most of all the disadvantages of conventional breadboard. These also avoid the use of thin wires for connecting the components; they are small in size and efficient in performance.
First of al the actual size circuit layout is to be drawn on the copper side of the copper clad board. Then enamel paint is applied on the tracks of connection with the help of a shade brush. We have to apply the paints surrounding the point at which the connection is to be made. It avoids the disconnection between the leg of the component and circuit track. After completion of painting work, it is allowed to dry.
Etching:
The removal of excess of copper on the plate apart from the printed circuit is known as etching. From this process the copper clad board
Printed circuit is placed in the solution of Fe2Cl3 with 3-4 drops of HCL in it and is kept so for about 10 to 15 minutes and is taken out when all the excess copper is removed from the P.C.B.
After etching, the P.C.B. is kept in clean water for about half an hour in order to get P.C.B. away from acidic, field, which may cause poor performance of the circuit. After the P.C.B. has been thoroughly wasted, paint is removed by soft piece of cloth dipped I thinner or turbine. Then P.C.B. is checked as per the layout, now the P.C.B. is ready for use.
After completion of painting work, holes 1/23inch (1mm) diameter are drilled at desired point where we have to fix the components.
Soldering is the process of joining two metallic conductor the joint where two metal conductors are to be join or fused is heated with a device called soldering iron and then as allow of tin and lead called solder is applied which melts and converse the joint. The solder cools and solidifies quickly to ensure is good and durable connection between the jointed metal converting the joint solder also present oxidation.
Soldering and Desoldering Techniques:
These are basically two soldering techniques.
Manual soldering with iron.
Mass soldering.
The surface to be soldered must be cleaned & fluxed. The soldering iron switched on and bellowed to attain soldering temperature. The solder in form of wire is allied hear the component to be soldered and heated with iron. The surface to be soldered is filled, iron is removed and joint is cold without disturbing.
Solder Joints Are Supposed To:
Provide permanent low resistance path. Make a robust mechanical link between P.C.B. and leads of components. Allow heat flow between component, joining elements and P.C.B.
The following precaution should be taken while soldering:
Use always an iron plated copper core tip for soldering iron. Slightly for the tip with a cut file when it is cold. Use a wet sponge to wipe out dirt from the tip before Soldering instead of asking the iron.
Tighten the tip screw if necessary before iron is connected to Power supply. Clean component lead and copper pad before soldering.
Apply solder between component leads, P.C.B. pattern and tip of soldering iron. Iron should be kept in contact with the joint for 2-3 seconds only instead of keeping for very long or very small time.
Cutting the leads:
Once we get our components, soldered into the circuit board, Surface mounting components onto a circuit board and takes the leads push through holes in the board, which some say is the easier of the two methods of soldering small components onto boards.
A photo resistor or LDR is a resistor whose resistanc e decreases with increasing incident light intensity; in other words, it exhibits photoconductivity.
< p>< p>< p>A photoresistor is made of a high resistance semiconductor. If light falling on the device is of high enough frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electron (and its hole partner) conduct electricity, thereby lowering resistance.;
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A photoelectric device can be either intrinsic or extrinsic. An intrinsic semiconductor has its own charge carriers and is not an efficient semiconductor, for example, silicon. In intrinsic devices the only available electrons are in the valence band, and hence the photon must have enough energy to excite the electron across the entire bandgap. Extrinsic devices have impurities, also called dopants, added whose ground state energy is closer to the conduction band; since the electrons do not have as far to jump, lower energy photons (that is, longer wavelengths and lower frequencies) are sufficient to trigger the device. If a sample of silicon has some of its atoms replaced by phosphorus atoms (impurities), there will be extra electrons available for conduction. This is an example of an extrinsic semiconductor. Photoresistors are basically photocells.
An IR LED, also known as IR transmitter, is a special purpose LED that transmits infrared rays in the range of 760 nm wavelength. Such LEDs are usually made of gallium arsenide or aluminum gallium arsenide. They, along with IR receivers, are commonly used as sensors.
The appearance is same as a common LED. Since the human eye cannot see the infrared radiations, it is not possible for a person to identify whether the IR LED is working or not, unlike a common LED. To overcome this problem, the camera on a cell phone can be used. The camera can show us the IR rays being emanated from the IR LED in a circuit.
FEATURES
In electronics, a common-emitter amplifier ; ; ;is one of three basic single-stage bipolar-junction-transi stor (BJT) amplifier topologies, typically used as a voltage amplifier. In this circuit the base terminal of the transistor serves as the input, the collector is the output, and the emitter is common to both (for example, it may be tied to ground reference or a power supply rail), hence its name. The analogous field-effect transistor circuit is the common-source amplifier, and the analogous tube circuit is the common-cathode amplifier.
AP PLICATIONS
DESCRIPTIONS
Temp. = 25 °c unless otherwise specified.
To distinguish left from right there is a gap between the C and bands. band A is first significant figure of component value (left side) band B is the second significant figure band C is the decimal multiplier
band D if present, indicates tolerance of value in percent (no band means 20%)
For example, a resistor with bands of yellow, violet, red, and gold will have first digit 4 (yellow in table below), second digit 7 (violet), followed by 2 (red) zeros: 4,700 ohms. Gold signifies that the tolerance is ±5%, so the real resistance could lie anywhere between 4,465 and 4,935 ohms.
Resistors manufactured for military use may also include a fifth band which indicates component failure rate (reliability); refer to MIL-HDBK-199 for further details.
Tight tolerance resistors may have three bands for significant figures rather than two, or an additional band indicating temperature coefficient, in units of ppm/K.
Resistors use preferred numbers for their specific values, which are determined by their tolerance. These values repeat for every decade of magnitude: 6.8, 68, 680, and so forth. In the E24 series the values are related by the 24th root of 10, while E12 series are related by the 12th root of 10, and E6 series by the 6th root of 10. The tolerance of device values is arranged so that every value corresponds to a preferred number, within the required tolerance.
Zero ohm resistors are made as lengths of wire wrapped in a resistor-shaped body which can be substituted for another resistor value in automatic insertion equipment. They are marked with a single black band.
The 'body-end-dot' or 'body-tip-spot' system was used for radial-lead (and other cylindrical) composition resistors sometimes still found in very old equipment; the first band was given by the body color, the second band by the color of the end of the resistor, and the multiplier by a dot or band around the middle of the resistor. The other end of the resistor was colored gold or silver to give the tolerance, otherwise it was 20%.
Extra bands on ceramic capacitors will identify the voltage rating class and temperature coefficient characteristics. A broad black band was applied to some tubular paper capacitors to indicate the end that had the outer electrode; this allowed this end to be connected to chassis ground to provide some shielding against hum and noise pickup.
Polyester film and "gum drop" tantalum electrolytic capacitors are also color coded to give the value, working voltage and tolerance.
Introduction:
A diode is an electrical device allowing current to move through it in one direction with far greater ease than in the other. The most common kind of diode in modern circuit design is the semiconductor diodes are symbolized in the schematic diagrams such as figure bellow. The term diode is customarily reversed for small signal devices, I ≤1A. The term rectifier is used for power devices, I >1A.
When placed in a simple battery lamp circuit, the diode will either allow or prevent current through the lamp, depending on the polarity of the applied voltage. (Figure below)
When the polarity of the battery is such that electrons are allowed flow through the diode, the diode is said to be forward biased. Conversely, when the battery is “backward” and the diode blocks current, the diode is said to be reversed biased. A diode may be through of as like a switch: “closed” when forward biased and “open” when reversed biased.
Oddly enough, the direction of the diode symbols “arrowhead” points against the direction of electron flow. This is because the diode symbol was invented by engineers, who predominantly use conventional flow notation in their schematics, showing current as a flow of charge from the positive side of the voltage source to the negative. This convention holds true for all semiconductors symbol possessing “arrowheads” the arrow points in the permitted direction of conventional flow, and against the permitted direction of electron flow. Diode behavior is analogous to the behavior of a hydraulic device called a check valve. A check valve arrows fluid flow through it in only one direction.
Lik e check valves, diodes are essentially “pressure” operated (voltage operated) devices. The essential difference between forward bias and reverse bias is the polarity of the voltage dropped across the diode. Let’s take a closer look at the simple battery-diode-lamp circuit shown earlier, this time investigating voltage drops across the various components.
A forward-biased diode conducts current and drops small voltage across it, leaving most of the battery voltage dropped across the lamp. If the battery’s polarity is reversed, the diode become reversed-biased, and drops all of the battery’s voltage leaving none for the lamp. If we consider the diode to be a self actuating switch (closed in the forward-bias mode and open in the reversed-bias mode), this behavior makes sense. The most substantial difference is that the diode drops a lot more voltage when conducting than the average mechanical switch (0.7 volts verses tens of mille volts).
This forward-bias voltage drop exhibited by the diode is due to the action of the depletion region formed by the P-N junction under the influence of an applied voltage. If no voltage is applied across the semi conductor diode, a thin depletion region exists around the region of the P-N junction, preventing current flow, fig. below (a) the depletion region is almost devoid of the available charge carriers, and acts as an insulator.
The schematic symbol of the diode is shown in above fig. (b) Such that the anode (pointing end) corresponds to the P-type semi conductor at fig. (a) The cathode bar, non-pointing end, at fig. (b) corresponds the N-type material at fig. (b) Also note that the cathode stripe on the physical part fig. (c) Corresponds to the cathode on the symbol . If a reverse-biasing voltage is applied across the P-N junction, this depletion region expands, further resisting any current through it. As shown below in fig. (d). conversely, if a forward-biasing voltage is applied across the P-N junction, the depletion region collapses and becomes thinner. The diode becomes less resistive to the current through it. In order for a sustained current to go through the diode; through, the depletion region must be fully collapsed by the applied voltage. This takes a certain minimum voltage to accomplish, the forward voltage as shown in fig. (e) For silicon and germanium diodes, the forward voltage is 0.7V and 0.3V respectively. Forward voltage drops remains approximately constant for a wide range of diode currents, meaning that the diode voltage drop is not like that of a resistor or even closed switch. For most simplified circuit analysis, the voltage drop across a conducting diode may be considered constant at the nominal figure and not related to the amount of current.
How to Connect a Protection Diode in a circuit:
A protection diode is used in a circuit so that current will not flow in the reverse direction in the circuit because a diode only allows the current to flow in a one direction in a circuit, it can protect components in a circuit that are to the current that flows through them in the wrong direction. A protection diode is connected in a circuit by placing the diode in the series with the circuitry that is to be protected. For example, in this project protection diode is connected in series with LED. LED is very sensitive to current in the reverse direction. It can handle a certain amount of current in reverse direction. If enough reverse voltage drop across the LED, the LED Will break down and allow current to flow through it in the reverse direction, which can cause the LED to be permanently damaged. Circuit diagram for connection of protection diode is shown below
Sensor block:
Sensor block has LDR, Transistor, resistor and LED. LDR senses light and gives corresponding response to its resistance. This resistance is converted into voltage drop as V=IR. Transistor amplifies this voltage and send to the microcontroller to process it.
Processor block has timer circuit that decide how longer shoulder alarm and buzzer will ON. This circuit also store single bit memory for output compatibility.
Output block has LEDs and BUZZER. This device are used to indicate any interruption at boundary of the system.
Complete Boundary security system model is shown below:
Posted By :
Mahesh Nigam
(Scientist)
2019-09-27 17:13
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