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 Project overview  Block diagram  Power supply  Microcontroller  MAX232 & DB9 Connector  Relay  Relay driver  Software requirements  Schematic & Working of the project  Advantages  Applications  Future scope  Conclusion

 This project constitutes external load for home applications controlled with the help of PC.  An Embedded project is a combination of hardware and software, designed to perform a specific task.  In embedded technology, the embedded programming is burnt into the microcontroller.  PC is connected to microcontroller through a level shifter IC, ULN2003 (Driver) is used to drive the relays, and from relays we can connect external devices.  MAX-232 is used as voltage level shifter because PC voltage levels and microcontroller voltage levels are different. DB9 (RS-232) connector is used to connect to PC com port.  It can also manage a new economical solution of theater light control systems.

Step down transformer Bridge rectifier Filter Regulator

 The 230V AC supply is first stepped down to 12V AC using a step down transformer.  This is then converted to DC using bridge rectifier.  The AC ripples is filtered out by using a capacitor and given to the input pin of voltage regulator  At output pin of this regulator we get a constant 5V DC which is used for MC and other ICs in this project.

 It is a smaller computer  Has on-chip RAM, ROM, I/O ports... RAM ROM I/O Port Timer Serial COM Port Microcontroller CPU A single chip

CPU On-chip RAM On-chip ROM for program code 4 I/O Ports Timer 0 Serial Port OSC Interrup t Control External interrupts Timer 1 Timer/Counter Bus Control TxD RxD P0 P1 P2 P3 Address/Data Counter Inputs

 8K Bytes of In-System Programmable (ISP) Flash Memory  4.0V to 5.5V Operating Range  Fully Static Operation: 0 Hz to 33 MHz  256 x 8-bit Internal RAM  32 Programmable I/O Lines  Three 16-bit Timer/Counters  Eight Interrupt Sources  Full Duplex UART Serial Channel

+5V 30 pF 8.2 K 10 uF MHz EA/VPP X1 X2 RST

 The MAX232 is an integrated circuit that converts signals from an RS-232serial port to signals suitable for use in TTL compatible digital logic circuits.  The MAX232 is a dual driver/receiver and typically converts the RX, TX, CTS and RTS signals.  When a MAX232 IC receives a TTL level to convert, it changes a TTL Logic 0 to between +3 and +15V, and changes TTL Logic 1 to between -3 to -15V, and vice versa for converting from RS232 to TTL.

 The DB9 (originally DE-9) connector is an analog 9-pin plug of the D-Sub miniature connector family.

 A relay is an electrically operated switch.  Current flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch contacts.  The coil current can be on or off so relays have two switch positions and have double throw (changeover) switch contacts as shown in the diagram.

 Relays allow one circuit to switch a second circuit which can be completely separate from the first.  For example a low voltage battery circuit can use a relay to switch a 230V AC mains circuit.  There is no electrical connection inside the relay between the two circuits, the link is magnetic and mechanical.  To drive relay through MC ULN2003 relay driver IC is used

 ULN is Relay driver application  The ULN2003 is a monolithic high voltage and high current Darlington transistor arrays.  It consists of seven NPN Darlington pairs that features high-voltage outputs with common- cathode clamp diode for switching inductive loads.  The collector-current rating of a single Darlington pair is 500mA.  The Darlington pairs may be paralleled for higher current capability.

 The ULN functions as an inverter.  If the logic at input 1B is high then the output at its corresponding pin 1C will be low.

 Keil an ARM Company makes C compilers, macro assemblers, real-time kernels, debuggers, simulators, integrated environments, evaluation boards, and emulators for ARM7/ARM9/Cortex-M3, XC16x/C16x/ST10, 251, and 8051 MCU families.  Compilers are programs used to convert a High Level Language to object code. Desktop compilers produce an output object code for the underlying microprocessor, but not for other microprocessors.

 i.e the programs written in one of the HLL like ‘C’ will compile the code to run on the system for a particular processor like x86 (underlying microprocessor in the computer).  For example compilers for Dos platform is different from the Compilers for Unix platform So if one wants to define a compiler then compiler is a program that translates source code into object code.

 The project uses a PC to control the loads.  The commands are received by the micro controller through level shifted IC Max232.  When the program is executed, it drives relay from the microcontroller through relay driver IC ULN2003.  Load’s are switched ON and switched OFF based on the corresponding command sent from the keyboard through hyperterminal.  As per the program, the loads will be turned ON and OFF through the relays.