Brief Project Description: yEstablishing a connection with a transformer from 220v AC. yConverting and Forwarding 12Vo lts Ac from transformer. yBridge Rectifier is used for converting 12Vo lt Ac Voltage to 15Volt DC voltage. yFour ICS are used in this project. yThree capacitor are also used for Smoothing & Controlling the Distortion. Alternating Current (AC) yAlternating Current (AC) flows one way, then the ot her way, continually reversing direction. yAn AC voltage is continually changing between positive (+) and negative (-). yThe rate of changing d irection is called the frequency of the AC and it is measured in hertz (Hz) which is the number of forwards-backwards cycles per second. yMains electricity in the UK has a frequency of 50Hz. yAn AC supply is suitable for powering so me devices such as lamps and heaters but almost all electronic circuits require a steady DC supply. Direct Current (DC) Direct Current (DC) always flows in the same direction, but it may increase and decrease. A DC voltage is always positive (or always negative), but it may increase a nd decrease. Electronic circuits normally require a steady DCsupply which is constant at one value or a smooth DC supply which has a small variation called ripple. Cells, batteries and regulated power supp lies provide steady DC which is ideal for electronic circuits. Power supplies contain a transformer which conve rts the mains AC supply to a safe low voltage AC. Then the AC is converted to DC by a bridge rectifier but the output is varying DC which is unsuitable for electronic circuits. Some power supplies include a capacitor to provide smooth DC which is suitable for less-s ensitive electronic circuits.
Transcript
8/8/2019 Control Electrical Home Appliances Using Computer
y Establishing a connection with a transformer from 220v AC. y Converting and Forwarding 12Volts Ac from transformer. y B ridge Rectifier is used for converting 12Volt Ac Voltage to 15Volt DC voltage. y Four ICS are used in this project. y T hree capacitor are also used for Smoothing & Controlling the Distortion.
Alternating Current (AC)
y Alternating Current (AC) flows one way, then the other way, continually reversing direction.y An AC voltage is continually changing between positive (+) and negative (-).y T he rate of changing direction is called the frequency of the AC and it is measured in hertz (Hz) which is
the number of forwards-backwards cycles per second .y M ains electricity in the UK has a frequency of 50Hz.y An AC supply is suitable for powering some devices such as lamps and heaters but almost all electronic
circuits require a steady DC supply.
Direct Current (DC)
Direct Current (DC) always flows in the same direction, but it may increase and decrease. A DC voltage is always positive (or always negative), but it may increase and decrease. Electronic circuits normally require a steady DC supply which is constant at one value or a smooth DC supply which has a small variation called ripple . Cells,
batteries and regulated power supplies provide steady DC which is ideal for electronic circuits.
Power supplies contain a transformer which converts the mains AC supply to a safe low voltage AC. T hen the ACis converted to DC by a bridge rectifier but the output is varying DC which is unsuitable for electronic circuits.
Some power supplies include a capacitor to provide smooth DC which is suitable for less-sensitive electroniccircuits.
8/8/2019 Control Electrical Home Appliances Using Computer
T here are many types of power supply. M ost are designed to convert high voltage AC mains electricity to asuitable low voltage supply for electronic circuits and other devices. A power supply can by broken down into aseries of blocks, each of which performs a particular function.
For example a 5V regulated supply:
Transformer only:
T he low voltage AC output is suitable for lamps, heaters and special AC motors. It is not suitable for electronic circuitsunless they include a rectifier and a smoothing capacitor.
8/8/2019 Control Electrical Home Appliances Using Computer
T he varying DC output is suitable for lamps, heaters and standard motors. It is not suitable for electronic circuits unlessthey include a smoothing capacitor.
Transformer + Rectifier + Smoothing:
T he smooth DC output has a small ripple. It is suitable for most electronic circuits.
Transformer + Rectifier + Smoothing + Regulator:-
T he regulated DC output is very smooth with no ripple. It is suitable for all electronic circuits.
Transformer:
T ransformers convert AC electricity from one voltage to another with little loss of power. T ransformers work only with ACand this is one of the reasons why mains electricity is AC. T he input coil is called the primary and the output coil is calledthe secondary . T here is no electrical connection between the two coils; instead they are linked by an alternating magneticfield created in the soft-iron core of the transformer. T he two lines in the middle of the circuit symbol represent the core.
8/8/2019 Control Electrical Home Appliances Using Computer
A bridge rectifier can be made using four individual diodes, but it is also available in special packages containing the four
diodes required. It is called a full-wave rectifier because it uses all the AC wave (both positive and negative sections). 1.4Vis used up in the bridge rectifier because each diode uses 0.7V when conducting and there are always two diodes conducting
Smoothing
Smoothing is performed by a large value electrolytic capacitor connected across the DC supply to act as a reservoir,supplying current to the output when the varying DC voltage from the rectifier is falling. T he diagram shows theunsmoothed varying DC (dotted line) and the smoothed DC (solid line). T he capacitor charges quickly near the peak of thevarying DC, and then discharges as it supplies current to the output.
8/8/2019 Control Electrical Home Appliances Using Computer
T he circuit consists of two main parts - ULN2803 IC and a 5 pin Relay. Working of both of them is explained below:-
Working of Relay
A relay is an electrically operated switch. It allows one circuit to switch a second circuit which is completelyseparated from the first. For example a low voltage battery circuit can use a relay to switch a 230V AC mainscircuit. T here is no electrical connection inside the relay between the two circuits, the link is magnetic andmechanical.
In the above figure, when controlling switch is closed, current flows through the coil and thus, magnetic field is produced. T he resulting magnetic field attracts an armature that is mechanically linked to a set of contacts. T hemovement makes a connection with a fixed contact and circuit gets completed. When the current to the co il isswitched off, the armature is returned by a force approximately half as strong as the magnetic force to its relaxed
position and the connection is broken.
T he relay's switch connections are usually labeled CO M , N/C and N/O:
y CO M = Common, always connect to this, it is the moving part of the switch.y N/C = Normally Closed, CO M is connected to this when the relay coil is off.y N/O = Normally Open, CO M is connected to this when the relay coil is on.
y Connect to CO M and N/O if you want the switched circuit to be on when the relay coil is on.y Connect to CO M and N/C if you want the switched circuit to be on when the relay coil is off.
Working of ULN2803 IC IntroductionIC ULN2803 consists of octal high voltage, high current darlington transistor arrays. T he eight NPN Darlingtonconnected transistors in this family of arrays are ideally suited for interfacing between low logic level digitalcircuitry (such as TT L, C M OS or P M OS/N M OS) and the higher current/voltage requirements of lamps, relays,
printer hammers or other similar loads for a broad range of computer, industrial, and consumer applications.
8/8/2019 Control Electrical Home Appliances Using Computer
y Eight Darlington¶s with Common Emitter.y Open±collector outputs.y Freewheeling clamp diodes for transient suppression.y Output Current to 500 mA.y Output Voltage to 50 V.y Inputs pinned opposite outputs to simplify board layout.
Pin out
Working
T he ULN 2803 IC consists of eight NPN Darlington connected transistors (often called a Darlington pair).Darlington pair consists of two bipolar transistors such that the current amplified by the first is amplified further
by the second to get a high current gain or h FE. T he figure shown below is one of the eight Darlington pairs of ULN 2803 IC.
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Case 1: When IN is 0 volts. Q1 and Q2 both will not conduct as there is no base current provided to them. T hus, nothing will appear at theoutput (OU T ).
Case 2: When IN is 5 volts.
Input current will increase and both transistors Q1 and Q2 will begin to conduct. Now, input current of Q2 iscombination of input current and emitter current of Q1, so Q2 will conduct more than Q1 resulting in higher current gain which is very much required to meet the higher current requirements of devices like motors, relaysetc. Output current flows through Q2 providing a path (sink) to ground for the external circuit that the output isapplied to. T hus, when a 5V input is applied to any of the input pins (1 to 8), output voltage at correspondingoutput pin (11 to 18) drops down to zero providing GND for the external circuit. T hus, the external circuit getsgrounded at one end while it is provided +V cc at its other end. So, the circuit gets completed and starts operating.
Circuit working
working of this circuit is very simple. When data at pin 2 is '1', i.e., when 5V is coming out of pin 2 then, pin 1 of ULN2803 IC receives 5V input and thus its pin 18 provides GND to one end of relay coil. T he other end of relaycoil is given +Vcc (12V), so the coil gets energized and the CO M gets connected to the N/O contact and the ACmains circuit gets completed and the bulb glows.
Now, bulb will glow as long as data at pin 2 is high. When data at pin 2 becomes low, then the GND provided by
pin 18 of ULN2803 IC vanishes and coil gets de-energized and thus CO M is connected back to N/C contact.T hus, external AC mains circuit is broken and bulb stops glowing.
