PROGRAMMABLE AC POWER CONTROL SUBMITTED BY

ABSTRACT Based on the principle of firing angle control of thyristors, one can control the ac power. A display unit displays the full power or any percentage and one can enter the desired percentage to reduce the power to the load. The firing angle would be automatically adjusted to maintain the load power. The project uses a lamp such that the entered power matches the required one. The above operation is carried out by using a TRIAC in series with the AC load. (optionally two no’s of SCRs connected in back to back can also be used) It uses microcontroller from 8051 family. The input is given to the Microcontroller using a keypad and ZVS is given as reference. A 16X2 LCD is used for display purpose. The power supply consists of a step down transformer 230/12V, which steps down the voltage to 12V AC. This is converted to DC using a Bridge rectifier. The ripples are removed using a capacitive filter and it is then regulated to +5V using a voltage regulator 7805 which is required for the operation of the microcontroller and other components.

BLOCK DIAGRAM

HARD WARE EQUIPMENTS POWER SUPPLY BLOCK MICROCONTROLLER (AT89S52/AT89C51) LCD DISPLAY KEYPAD LM358 (COMPARATOR) MOC3021 BC547 1N4007 LED RESISTORS & CAPACITORS SCR

EMBEDDED SYSTEMS Definition for :- EMBEDDED SYSTEMS A combination of hardware and software which together form a component of a larger machine. An example of an embedded system is a microprocessor that controls an automobile engine. An embedded system is designed to run on its own without human intervention, and may be required to respond to events in real time.

EMBEDDED SYSTEMS

AT89S52 MICRO CONTROLLER Compatible with MCS®-51 Products 8K Bytes of In-System Programmable (ISP) Flash Memory 4.0V to 5.5V Operating Range Crystal Frequency 11.0592MHZ Three-level Program Memory Lock 256 x 8-bit Internal RAM 32 Programmable I/O Lines Three 16-bit Timer/Counters Eight Interrupt Sources Full Duplex UART Serial Channel Watchdog Timer AT89S52

PIN DIAGRAM OF AT89S52

LED LEDs are semiconductor devices are made out of silicon When current passes through the LED, it emits photons as a byproduct. Normal light bulbs produce light by heating a metal filament until its white hot LEDs present many advantages over traditional light sources including lower energy consumption, longer lifetime, improved robustness, smaller size and faster switching

THYRISTOR (SCR) A silicon-controlled rectifier (or semiconductor-controlled rectifier) is a four-layer solid state device that controls current The name "silicon controlled rectifier" or SCR is General Electric's trade name for a type of thyristor An SCR consists of four layers of alternating P and N type semiconductor materials. Silicon is used as the intrinsic semiconductor, to which the proper dopants are added The doping of PNPN will depend on the application of SCR, since its characteristics are similar to those of the thyratron

BC547 The BC547 transistor is an NPN Epitaxial Silicon Transistor. The BC547 transistor is a general-purpose transistor in small plastic packages. It is used in general-purpose switching and amplification BC847/BC547 series 45 V, 100 mA NPN general-purpose transistors. Whenever base is high, then current starts flowing through base and emitter and after that only current will pass from collector to emitter  

MOC3021 ( OPTO COUPLER ) Opto-couplers are made up of a LED and a light sensitive device, all wrapped up in one package no electrical connection between the two devices The light sensitive device may be a photodiode, phototransistor, or more esoteric devices such as thyristors, triacs etc.  

LM 358 ( COMPARATOR ) Internally frequency compensated for unity gain. Large dc voltage gain: 100 Db. Wide bandwidth (unity gain): 1 MHz (temperature compensated) Wide power supply range: Single supply: 3V to 32V or dual supplies: ±1.5V to ±16V Very low supply current drain (500 µA)-essentially independent of supply voltage. Low input offset voltage: 2 mV Input common-mode voltage range includes ground. Differential input voltage range equal to the power supply voltage.

LM 358 PIN DIAGRAM 1 - Output 1 2 - Inverting input 3 - Non-inverting input 4 – VCC- 5 - Non-inverting input 2 6 - Inverting input 2 7 - Output 2 8 – VCC+

Keypad A keypad is a set of buttons arranged in a block or "pad" which usually bear digits, symbols and usually a complete set of alphabetical letters. If it mostly contains numbers then it can also be called a numeric keypad. In order to detect which key is pressed from the matrix, the row lines are to be made low one by one and read the columns. Assume that if Row1 is made low, then read the columns. If any of the key in row1 is pressed then correspondingly the column 1will give low that is if second key is pressed in Row1, then column2 will give low.

LIQUID CRYSTAL DISPLAY (LCD) Most common LCDs connected to the microcontrollers are 16x2 and 20x2 displays. This means 16 characters per line by 2 lines and 20 characters per line by 2 lines, respectively. The standard is referred to as HD44780U, which refers to the controller chip which receives data from an external source (and communicates directly with the LCD.

LCD BACKGROUND If an 8-bit data bus is used the LCD will require 11 data lines (3 control lines plus the 8 lines for the data bus) The three control lines are referred to as EN, RS, and RW EN=Enable (used to tell the LCD that you are sending it data) RS=Register Select (When RS is low (0), data is treated as a command) (When RS is High(1), data being sent is text data ) R/W=Read/Write (When RW is low (0), the data written to the LCD) (When RW is low (0), the data reading to the LCD)

Zero voltage cross detection means the supply voltage waveform that passes through zero voltage for every 10msec of a 20msec cycle. We are using 50Hz ac signal, the total cycle time period is 20msec (T=1/F=1/50=20msec) in which, for every half cycle (i.e. 10ms) we have to get zero signals. This is achieved by using pulsating dc after the bridge rectifier before being filtered. For that purpose we are using a blocking diode D3 between pulsating dc and the filter capacitor so that we can get pulsating DC for use. The pulsating DC is given to potential divider of 1k and 4.7k to deliver an output about 5V pulsating from 12V pulsating which is connected to non inverting input of comparator pin 3. Here Op-amp is used as comparator. The 5V DC is given to a potential divider of 6.8K and 10k which gives an output of about 1.06V and that is connected to inverting input pin no 2.One resistance of 1K is used from output pin 1 to input pin 2for feedback. As we know the principle of a comparator is that when non-inverting terminal is greater than the inverting terminal then the output is logic high (supply voltage) .Thus the pulsating dc at pin no 3 is compared with the fixed dc of 1.06V at pin no 2. The o/p of this comparator is fed to the inverting terminal of another comparator. The non-inverting terminal of this comparator pin no 5 is given a fixed reference voltage i.e., 2.5V taken from a voltage divider formed from resistors of 10k and 10k. Thus we get ZVR (Zero Voltage Reference) detection. This ZVR is then used as input pulses to microcontroller.

First the lamp glows at full intensity First the lamp glows at full intensity. Using keypad enter the required percentage of the power. This input is taken by the controller and it generates the PWM pulses for the required % of power entered which is given to pin 2 of MOC3021 IC and it maintains the power. This % of power is displayed on LCD. To change the intensity of power keypad is used as an input to the micro controller.

SOFTWARE REQUIREMENTS PROGRAMMING LANGUAGES Embedded C , ALP (Assembly Language) COMPILERS: Keil 2.0/3.0uv DUMPING SOFT WARE: Using Micro controller flash Software we are dumping our HEX Code into Micro Controller

KEIL COMPILER WINDOW

BIBILOGRAPHY The 8051 Microcontroller and Embedded systems” by Muhammad Ali Mazidi and Janice Gillispie Mazidi , Pearson Education. ATMEL 89S52 Data Sheets. www.atmel.com www.beyondlogic.org www.wikipedia.org www.howstuffworks.com www.alldatasheets.com

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