PROGRAMMABLE SECURITY CODE LOCK

PROGRAMMABLE SECURITY CODE LOCK

1. INTRODUCTION

Today everybody is very conscious about the security of their assets and home appliance. So home security system is very popular nowadays but it also have some drawbacks. In case conventional home security system, anyone can operate it that means any one can switch it on or off without permission of the owner. Introduction of code lock home security system can greatly solve this problem. By using this system only user can operate home security system. In this system, when correct code is entered the controller senses it and triggers motor and whenever faulty code is entered the microcontroller senses it and alarm turns on. Hence user can change the code and can keep it secret.

This project is very useful for door security applications. It operates a relay( for example to open a door) for a few seconds when a valid code is entered. The secret code can be changed any time after entering the current code. The kit includes the relay for door lock.

Now a days security must require for our home as well as office. Here the micro controlled based digital code lock an access control system that allow only authorized person to access a restricted area. When an authorized person enters the predetermined number via keypad the relay operates for a limited time ( its about 6 seconds) or jumper setting J1 show on the circuit board sets continuous. It shows relay can be used up to operate solenoid, solenoid is an electronic lock, which can be used to open/close door. When the code has been enters in corrected five times in row keypad will be locked for few minutes, and it will be switched on the alarm.

2. BLOCK DIAGRAM

3. CIRCUIY DIAGRAM

4. PROJECT DESCRIPTIONMICRO CONTROLLER:A Micro controller is used for controlling entire circuits and to maintain timings. Here a micro controller named AT89c51 from Atmel Corporation is used for that purpose. AT89c51 is an bit micro controller has 40 pins arranged in 4 I/O ports, that ports are used here for connecting to interface with the load. Micro controllers RESET pin is connected to an RC circuit as shown in above figure. This will give a high pulse to the RESET pin at time of starting. This will reset the micro controller means start execution from 0000h. It is essential for a micro controller circuit. When the power is switched ON charge in capacitor will be zero then the reset pin will get high voltage, capacitor starts charging then the voltage across the RST pin will decrease, micro controller starts execution.

KEY PAD In code lock circuit keypad is made using 12paces, of micro switches sw1 to sw9 is used for enter 0to 9 numbers. Sw10 is used for code change, sw11 is used for enter the code.

OPERATIONFirst enter your right password by using number key 0 to 9. If your password is right LED L2 glows and relay is energized. For code change enter your old password and push code change key sw10, LED L3 will glows, now enter new code.

LED INDICATORL1 - LED used for power indicator.L2 - relay status indicatorL3 - this LED will glow when you want to change codeL4 - this LED will glow when wrong password is entering for five times serially.

TECHANICAL FEATUREUp to 32 digits password can be acceptedBattery backup facility is providedPassword can be changed at any timeMaster/Slave password facilityWrong password indication

5. PART LIST FOR CODE LOCKResistorsR1 to R4, R8 330 , orange brown goldenR5 8K2 grey red red goldenR6,R7,R9,R101k brown black red goldenRN1 RN210K resistor network 9 pinCapacitorsCD1,CD2 33PF ceramic discC3 10 uF / 25v electrolyte capacitorC4,C6100KPF -104-0.1 uFceramic discC51000uF/16v/25v electrolyte capacitorC7100uF/ 16v electrolyte capacitorSemiconductor U1 AT89c51/52 micro controllerU2,U3 SN74LS 373U4 LM7805 +5v regulator ICQ1,Q3 BC547 NPN transistorQ2,Q4 BC 548 NPN transistorL1,L4,L5 red LED 5mmL3 green LEDL2 yellow LEDD1 to D4 1N4007 rectifier diode

Miscellaneous IC socket 40 pin 120 pin 2X1 11.0592 crystal oscillatorSwitch 1 to133 leg tactile switch reset 2 leg switcjRelay 12 v 1CO PCB mount relayCN2 3 pin burgsstrip with jumper switchBuzzer continuous typeTransformer 12v 500mA Two Pencil cell 1.5 v for dc motorCell containerPlywood Dc motor drive for door lockMain cord 2pin main cord for 230v ac power

RESISTORSExample: Circuit symbol: FunctionResistors restrict the flow of electric current, for example a resistor is placed in series with a light-emitting diode (LED) to limit the current passing through the LED.

CAPACITORS

The capacitor's function is to store electricity, or electrical energy. The capacitor also functions as a filter, passing alternating current (AC), and blocking direct current (DC).This symbol is used to indicate a capacitor in a circuit diagram. The capacitor is constructed with two electrode plates facing each other, but separated by an insulator.When DC voltage is applied to the capacitor, an electric charge is stored on each electrode. While the capacitor is charging up, current flows. The current will stop flowing when the capacitor has fully charged.

DIODESExample: Circuit symbol: FunctionDiodes allow electricity to flow in only one direction. The arrow of the circuit symbol shows the direction in which the current can flow. Diodes are the electrical version of a valve and early diodes were actually called valves. Light Emitting Diodes (LEDs)Example: Circuit symbol: FunctionLEDs emit light when an electric current passes through them.

6. MAJOR COMPONENTS OF CODE LOCKA. Key padIn access control system circuit keypad is made using 12 pcs. Of micro switches sw1 to sw10 is using for 0-9 number.sw10 is used for code changes.sw11 is usesd for enter the code. When this all this keys at logic high no key is pressed and when any of pin output goes low the two of output is made logic high and even then if the input pin remains low then the key of the column which is not made high is pressed. In this way key board is sensed by the microcontroller.

FIGURE FROM XEROX

B. REGULATOR IC 7805

It is a 3 terminal positive voltages regulator. This is used to make the stable voltage of +5v for MCU the lm7805 is three terminal positive regulator are available in the TO220 $ T03 package and with several fixed output voltage, making them useful in a wide range of applications. Each type of employs internal current limiting, thermal shutdown and save operating area protection, making it essentially indestructible. If adequate heat sinking is provided, they can deliver over 1A output current. Al through designed primarily as fixed voltage regulators. For more information please refer data sheet of LM7805PIN DIAGRAM

PIN DISCRIPTIONPIN NO.FUNCTIONNAME

1Input voltage (5V-18V)input

2Ground (0 V)ground

3Regulated output; 5V (4.8V-5.2V)output

C. POWER SUPPLY:-

Power supply is used to drive the circuit. Inappropriate voltage will damage the entire circuitry therefore it constitutes a very important part of the circuit.Every electronic circuit requires power for its operation. Every function simple or complex is controlled by the power supply. Even a little variation in voltage can damage all the circuitry. So power supply is of prime importance in all the circuits. The power supply which we get is a.c. operating at 220Volts.But as our electronic circuits work only on d.c. therefore; we cannot employ direct usage of supply which we get. In order to overcome this, we require various process namely transformation, rectification, smoothing or filtering and regulation. These entire process using bridge rectifiers are illustrated below:

Bridge rectifier is use to convert 12 AC into 12 DC voltage. Two supply voltage are for the circuit. A 12V AC from transformer is connected to bridge rectifier (D1-D4).All ICs are supplied with a regulator 5v from a LM7805 Fixed voltage regulator. The unregulated voltage of approximately 12V is required for the relay driving circuit

FIGURE FROM XEROX

TRANSFORMATION:-As already discussed the supply which we get is 220V A.C. supply. In order to decrease the magnitude of the voltage we make use of step down transformer. This transformer has more windings in the primary coil than in the secondary coil. So the voltage output at the secondary is an A.C. supply with magnitude less than 220V as shown below:

RECTIFICATION:-As all the electronic circuits work on DC therefore this low voltage A.C. cannot be directly fed to our circuit. Thus a process of rectification is required. In this process, A.C. voltage is converted into D.C. voltage using two semiconductor rectifying diodes as shown below:

Now as the two diodes D1 and D2 are connected in the opposite manner. Therefore one of the diode gets forward biased during the positive half of the a.c input and other gets forward biased during the negative half of the a.c. input. Thus during the positive half cycle rectification takes place through diode D1(diode D2 being reverse biased, cannot rectify) and during the negative half cycle, the rectification takes place through the diode D2(diode D1 being reverse biased, cannot rectify). But as at least one of the diode always remain in the conducting mode therefore both the halves of the a.c. input gets rectified and hence the name full wave rectifier.

SMOOTHING/FILTRATIONThe output of the rectification process is a varying D.C. As the D.C. waveform cannot be varying so it means that rectification is not 100% efficient due to which there is still some component of the input A.C. present in the D.C. voltage which is responsible for the variation. So in order to remove this A.C. component we require filtration or smoothing of the signal. This can be done using an electrolytic capacitor of 2200uf. As the capacitor offers infinite impedance to the D.C. signal and Zero impedance to the A.C. signal therefore, it allows the A.C. component to pass through and blocks the D.C. component. This means it will filter out the D.C. component from the input signal. Thus the output of the process will be a pure D.C. supply as shown below:

Now there is still some variation indicating that output D.C. voltage is not having constant magnitude. This is due to the capacitor used for filtration. Its time of charging and discharging are not equal due to which the filtration is not up to the mark. For making the output voltage assume a constant value we need a voltage regulator.

REGULATION:-Voltage regulator is used for this purpose mainly from the series of 78- - of the transistor. For getting the constant output of 5 volts we make use of 7805 voltage regulator. This process takes place as shown below:This completes all the processes. Now we have a constant D.C. supply with us which can be fed to any electronic circuit without any problem

D. RELAY AND BUZZER CIRCUITRELAY:-A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism, but other operating principles are also used. Relays find applications where it is necessary to control a circuit by a low-power signal, or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits, repeating the signal coming in from one circuit and re-transmitting it to another. Relays found extensive use in telephone exchanges and early computers to perform logical operations. A type of relay that can handle the high power required to directly drive an electric motor is called a contactor. Solid-state relays control power circuits with no moving parts, instead using a semiconductor device triggered by light to perform switching. Relays with calibrated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults; in modern electric power systems these functions are performed by digital instruments still called "protection relays"

RelaySymbolA 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 most 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. The coil of a relay passes a relatively large current, typically 30mA for a 12V relay, but it can be as much as 100mA for relays designed to operate from lower voltages. Most ICs (chips) cannot provide this current and a transistor is usually used to amplify the small IC current to the larger value required for the relay coil. The maximum output current for the popular 555 timer IC is 200mA so these devices can supply relay coils directly without amplification.Relays are usually SPDT or DPDT but they can have many more sets of switch contacts, for example relays with 4 sets of changeover contacts are readily available. For further information about switch contacts and the terms used to describe them please see the page on switches.

Relay inner view of coil and switch contactsMost relays are designed for PCB mounting but you can solder wires directly to the pins providing you take care to avoid melting the plastic case of the relay. The supplier's catalogue should show you the relay's connections. The coil will be obvious and it may be connected either way round. Relay coils produce brief high voltage 'spikes' when they are switched off and this can destroy transistors and ICs in the circuit. To prevent damage you must connect a protection diode across the relay coil. The animated picture shows a working relay with its coil and switch contacts. You can see a lever on the left being attracted by magnetism when the coil is switched on. This lever moves the switch contacts. There is one set of contacts (SPDT) in the foreground and another behind them, making the relay DPDT. The relay's switch connections are usually labeled COM, NC and NO: COM = Common, always connect to this; it is the moving part of the switch. NC = Normally Closed, COM is connected to this when the relay coil is off. NO = Normally Open, COM is connected to this when the relay coil is on. Connect to COM and NO if you want the switched circuit to be on when the relay coil is on. Connect to COM and NC if you want the switched circuit to be on when the relay coil is off.

RELAY AND BUZZER DRIVER CIRCUIT:A SPDT relay is connected to pin 22 of the microcontroller through a driver transistor and buffer IC . The relay required 12volt at a current of the around 50mA , which cannot provide by the micro controller . so the driver transistors are added . the relay is used to operate the external siren or for operating any other electrical device. Normally the relay remains off. As soon as pin 22 of the micro controller goes high, the transistors turn on and the relay operates.

FIGURE FROM XEROX

E. AT89C51/52 MICRO CONTROLLER

Features Compatible with MCS-51 Products 4K Bytes of In-System Reprogrammable Flash Memory Endurance: 1,000 Write/Erase Cycles Fully Static Operation: 0 Hz to 24 MHz Three-Level Program Memory Lock 128 x 8-Bit Internal RAM 32 Programmable I/O Lines Two 16-Bit Timer/Counters Six Interrupt Sources Programmable Serial Channel Low Power Idle and Power Down ModesDescriptionThe AT89C51 is a low-power, high-performance CMOS 8-bit microcomputer with 4K bytes of Flash Programmable and Erasable Read Only Memory (PEROM). The device is manufactured using Atmels high density nonvolatile memory technology and is compatible with the industry standard MCS-51 instruction set and pin out. The on-chip Flash allows the program memory to be reprogrammed in-system or by a conventional nonvolatile memory programmer. By combining a versatile 8-bit CPU with Flash on a monolithic chip, the Atmel AT89C51 is a powerful microcomputer which provides a highly flexible and cost effective solution to many embedded control applications.

PIN CONFIGURATION

FIGURE FROM XEREX

BLOCK DIAGRAM

The AT89C51 provides the following standard features: 4K bytes of Flash, 128 bytes of RAM, 32 I/O lines, two 16-bit timer/counters, a five vector two-level interrupt architecture, a full duplex serial port, on-chip oscillator and clock circuitry. In addition, the AT89C51 is designed with static logic for operation down to zero frequency and supports two software selectable power saving modes. The Idle Mode stops the CPU while allowing the RAM, timer/counters, serial port and interrupt system to continue functioning. The Power Down Mode saves the RAM contents but freezes the oscillator disabling all other chip functions until the next hardware reset.PIN DESCRIPTIONVCCSupply voltage.GNDGround.Port 0Port 0 is an 8-bit open drain bidirectional I/O port. As an output port each pin can sink eight TTL inputs. When 1s are written to port 0 pins, the pins can be used as high impedance inputs. Port 0 may also be configured to be the multiplexed loworder address/data bus during accesses to external program and data memory. In this mode P0 has internal pullups. Port 0 also receives the code bytes during Flash programming, and outputs the code bytes during program verification. External pullups are required during program verification.Port 1Port 1 is an 8-bit bidirectional I/O port with internal pull ups. The Port 1 output buffers can sink/source four TTL inputs. When 1s are written to Port 1 pins they are pulled high by the internal pull ups and can be used as inputs. As inputs, Port 1 pins that are externally being pulled low will source current (IIL) because of the internal pull ups. Port 1 also receives the low-order address bytes during Flash programming and verification.Port 2Port 2 is an 8-bit bidirectional I/O port with internal pull ups. The Port 2 output buffers can sink/source four TTL inputs. When 1s are written to Port 2 pins they are pulled high by the internal pull ups and can be used as inputs. As inputs, Port 2 pins that are externally being pulled low will source current (IIL) because of the internal pull ups. Port 2 emits the high-order address byte during fetches from external program memory and during accesses to external data memory that use 16-bit addresses (MOVX @ DPTR). In this application it uses strong internal pull ups when emitting 1s. During accesses to external data memory that use 8-bit addresses (MOVX @ RI), Port 2 emits the contents of the P2 Special Function Register. Port 2 also receives the high-order address bits and some control signals during Flash programming and verification.Port 3Port 3 is an 8-bit bidirectional I/O port with internal pullups. The Port 3 output buffers can sink/source four TTL inputs. When 1s are written to Port 3 pins they are pulled high by the internal pullups and can be used as inputs. As inputs, Port 3 pins that are externally being pulled low will source current (IIL) because of the pullups.Port 3 also serves the functions of various special features of the AT89C51 as listed below:

RSTReset input. A high on this pin for two machine cycles while the oscillator is running resets the device.ALE/PROGAddress Latch Enable output pulse for latching the low byte of the address during accesses to external memory. This pin is also the program pulse input (PROG) during Flash programming. In normal operation ALE is emitted at a constant rate of 1/6 the oscillator frequency, and may be used for external timing or clocking purposes. Note, however, that one ALE pulse is skipped during each access to external Data Memory. If desired, ALE operation can be disabled by setting bit 0 of SFR location 8EH. With the bit set, ALE is active only during a MOVX or MOVC instruction. Otherwise, the pin is weakly pulled high. Setting the ALE-disable bit has no effect if the microcontroller is in external execution mode.

PSENProgram Store Enable is the read strobe to external program memory. When the AT89C51 is executing code from external program memory, PSEN is activated twice each machine cycle, except that two PSEN activations are skipped during each access to external data memory.EA/VPPExternal Access Enable. EA must be strapped to GND in order to enable the device to fetch code from external program memory locations starting at 0000H up to FFFFH. Note, however, that if lock bit 1 is programmed, EA will be internally latched on reset. EA should be strapped to VCC for internal program executions. This pin also receives the 12-volt programming enable voltage (VPP) during Flash programming, for parts that require 12-volt VPP.XTAL1Input to the inverting oscillator amplifier and input to the internal clock operating circuit.XTAL2Output from the inverting oscillator amplifier.Oscillator CharacteristicsXTAL1 and XTAL2 are the input and output, respectively, of an inverting amplifier which can be configured for use as an on-chip oscillator, as shown in Figure 1. Either a quartz crystal or ceramic resonator may be used. To drive the device from an external clock source, XTAL2 should be left unconnected while XTAL1 is driven as shown in Figure 2. There are no requirements on the duty cycle of the external clock signal, since the input to the internal clocking circuitry is through a divide-by-two flip flop, but minimum and maximum voltage high and low time specifications must be observed.

Idle ModeIn idle mode, the CPU puts itself to sleep while all the on chip peripherals remain active. The mode is invoked by software. The content of the on-chip RAM and all the special functions registers remain unchanged during this mode. The idle mode can be terminated by any enabled interrupt or by a hardware reset. It should be noted that when idle is terminated by a hard ware reset, the device normally resumes program execution, from where it left off, up to two machine cycles before the internal reset algorithm takes control. On-chip hardware inhibits access to internal RAM in this event, but access to the port pins is not inhibited. To eliminate the possibility of an unexpected write to a port pin when Idle is terminated byReset , the instruction following the one that invokes Idle should not be one that writes to a port pin or to external memory.

7. SN74LS373 ICThe SN74LS373 consists of eight latches with 3-state outputs for bus organized system applications. The flip-flops appear transparent to the data (data changes asynchronously) when Latch Enable (LE) is HIGH. When LE is LOW, the data that meets the setup times is latched. Data appears on the bus when the Output Enable (OE) is LOW. When OE is HIGH the bus output is in the high impedance state. The SN74LS374 is a high-speed, low-power Octal D-type Flip-Flop featuring separate D-type inputs for each flip-flop and 3-state outputs for bus oriented applications. A buffered Clock (CP) and Output Enable (OE) is common to all flip-flops. The SN74LS374 is manufactured using advanced Low Power Schottky technology and is compatible with all ON Semiconductor TTL families

Eight Latches in a Single Package3-State Outputs for Bus InterfacingHysteresis on Latch EnableEdge-Triggered D-Type InputsBuffered Positive Edge-Triggered ClockHysteresis on Clock Input to Improve Noise MarginInput Clamp Diodes Limit High Speed Termination Effects

8. FABRICATION OF PCBThe PCB must be fabricated first. Then the components are soldered carefully to PCB. We should keep in mind that the quality of soldering affects the quality of output. The procedure for fabricating the PCB for setting up the circuit of any multi purpose project is described below.

PCB LAYOUT

PCB MAKINGMaking of Printed Circuits Boards (PCBs) is as much as art on a technique particularly so when they are to fabricated in very small numbers. There are several ways of drawing PCB patterns and making the final boards. The making of PCB patterns and making PCB essentially involves two steps.

1. Preparing the PCB drawing and2. Fabricating the PCB itself from the drawing.

The traditional method of drawing with complete placement of parts, taking a photographic negative of the drawing, developing the image of negative formed on photo sensitized copper plate and dissolving the excess copper by itching is a standard practice being followed in large scale operations. However, for small-scale operations, where large numbers of copies are not required, the cost saving procedure presented here may be adopted.

PCB DRAWINGMaking of PCB drawing involves some preliminary considerations such as placement of components on a piece of paper. Locating holes, deciding the diameters of various holes, the optimum area of each components should occupy the shape and location lands for connecting two or more components at a place, full space utilization and prevention of over crowding of components at a particular place. There is no other way to arrive at the conclusion than by trial and error. For anchoring leads of component 1mm diameter holes and for fixing PCB holding screws to the 3mm diameter holes can be made. Following these hints, a sketch of PCB is made.

PCB FABRICATIONThe copper clad PCB laminate is now prepared by rubbing away the oxide, grease etc. With fine emery paper or sand paper on this, the final PCB drawing may be traced by using a carbon paper. Clips are used to prevent the carbon paper from slipping while PCB pattern is being traced on the laminate. Only the connecting lines in PCBs, slants and holes, should be traced. The components position can be marked on the PCBs reverse side if desired.

The marked holes in PCB may be drilled using 1mm or 3mm drill bits and the traced PCB pattern created with black, quick drilling enamel paint, using a thin brush or a small metal case. In case, if there is any shorting of lines due to spilling of paint, there may be removed by scrapping with a blade or knife, after the paint has dried.

After drying, 20-30gms of Ferric chloride in 75ml of water may be heated to about 60deg and over the PCBs placed with its copper side upwards in a plastic tray. Stirring the solution helps speedy etching. The dissolution of unwanted copper would take about 45 minutes.

If etching takes longer, the solution may be heated again and the process is repeated. The paint on the pattern can be removed by rubbing with a rag soaked in thinner, turpentine or acetone. The PCB may then be washed and dried.

Depending on the wiring diagram, the resistors are taken care at first, and then the ICs are soldered.

SOLDERINGSoldering is a process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, the filler metal having a relatively low melting point. Soft soldering is characterized by the melting point of the filler metal, which is below 400C (800F). The filler metal used in the process is called solder.Soldering is distinguished from brazing by use of a lower melting-temperature filler metal; it is distinguished from welding by the base metals not being melted during the joining process. In a soldering process, heat is applied to the parts to be joined, causing the solder to melt and be drawn into the joint by capillary action and to bond to the materials to be joined by wetting action. After the metal cools, the resulting joints are not as strong as the base metal, but have adequate strength, electrical conductivity, and water-tightness for many uses. Soldering is an ancient technique mentioned in the Bible and there is evidence that it was employed up to 5000 years ago in Mesopotamia. ApplicationsOne of the most frequent applications of soldering is assembling electronic components to printed circuit boards (PCBs). Another common application is making permanent but reversible connections between copper pipes in plumbing systems. Joints in sheet metal objects such as food cans, roof flashing, rain gutters and automobile radiators have also historically been soldered, and occasionally still are. Jewelry components are assembled and repaired by soldering. Small mechanical parts are often soldered as well. Soldering is also used to join lead came and copper foil in stained glass work. Soldering can also be used to affect a semi-permanent patch for a leak in a container cooking vessel.SoldersSoldering filler materials are available in many different alloys for differing applications. In electronics assembly, the eutectic alloy of 63% tin and 37% lead (or 60/40, which is almost identical in performance to the eutectic) has been the alloy of choice. Other alloys are used for plumbing, mechanical assembly, and other applications.A eutectic formulation has several advantages for soldering; chief among these is the coincidence of the liquidus and solidus temperatures, i.e. the absence of a plastic phase. This allows for quicker wetting out as the solder heats up, and quicker setup as the solder cools. A non-eutectic formulation must remain still as the temperature drops through the liquidus and solidus temperatures. Any differential movement during the plastic phase may result in cracks, giving an unreliable joint. Additionally, a eutectic formulation has the lowest possible melting point, which minimizes heat stress on electronic components during soldering.Lead-free solders are suggested anywhere children may come into contact (since children are likely to place things into their mouths), or for outdoor use where rain and other precipitation may wash the lead into the groundwater. Common solder alloys are mixtures of tin and lead, respectively: 63/37: melts at 183 C (361.4 F) (eutectic: the only mixture that melts at a point, instead of over a range) 60/40: melts between 183190 C (361374 F) 50/50: melts between 185215 C (365419 F) Lead-free solder alloys melt around 250 C (482 F), depending on their composition.For environmental reasons, 'no-lead' solders are becoming more widely used. Unfortunately most 'no-lead' solders are not eutectic formulations, making it more difficult to create reliable joints with them. See complete discussion below; see also RoHS.Other common solders include low-temperature formulations (often containing bismuth), which are often used to join previously-soldered assemblies without un-soldering earlier connections, and high-temperature formulations (usually containing silver) which are used for high-temperature operation or for first assembly of items which must not become unsoldered during subsequent operations. Specialty alloys are available with properties such as higher strength, better electrical conductivity and higher corrosion resistance.FluxIn high-temperature metal joining processes (welding, brazing and soldering), the primary purpose of flux is to prevent oxidation of the base and filler materials. Tin-lead solder, for example, attaches very well to copper, but poorly to the various oxides of copper, which form quickly at soldering temperatures. Flux is a substance which is nearly inert at room temperature, but which becomes strongly reducing at elevated temperatures, preventing the formation of metal oxides. Secondarily, flux acts as a wetting agent in the soldering process, reducing the surface tension of the molten solder and causing it to better wet out the parts to be joined.Fluxes currently available include water-soluble fluxes (no VOC's required for removal) and 'no-clean' fluxes which are mild enough to not require removal at all. Performance of the flux needs to be carefully evaluated; a very mild 'no-clean' flux might be perfectly acceptable for production equipment, but not give adequate performance for a poorly-controlled hand-soldering operation.Traditional rosin fluxes are available in non-activated (R), mildly activated (RMA) and activated (RA) formulations. RA and RMA fluxes contain rosin combined with an activating agent, typically an acid, which increases the wettability of metals to which it is applied by removing existing oxides. The residue resulting from the use of RA flux is corrosive and must be cleaned off the piece being soldered. RMA flux is formulated to result in a residue which is not significantly corrosive, with cleaning being preferred but optional.BASIC SOLDERING TECHNIQUESMethodsSoldering operations can be performed with hand tools, one joint at a time, or en masse on a production line. Hand soldering is typically performed with a soldering iron, soldering gun, or a torch, or occasionally a hot-air pencil. Sheetmetal work was traditionally done with "soldering coppers" directly heated by a flame, with sufficient stored heat in the mass of the soldering copper to complete a joint; torches or electrically-heated soldering irons are more convenient. All soldered joints require the same elements of cleaning of the metal parts to be joined, fitting up the joint, heating the parts, applying flux, applying the filler, removing heat and holding the assembly still until the filler metal has completely solidified. Depending on the nature of flux material used, cleaning of the joints may be required after they have cooled.The distinction between soldering and brazing is arbitrary, based on the melting temperature of the filler material. A temperature of 450 C is usually used as a practical cut-off. Different equipment and/or fixturing is usually required since (for instance) a soldering iron generally cannot achieve high enough temperatures for brazing. Practically speaking there is a significant difference between the two processesbrazing fillers have far more structural strength than solders, and are formulated for this as opposed to maximum electrical conductivity. Brazed connections are often as strong or nearly as strong as the parts they connect, even at elevated temperatures."Hard soldering" or "silver soldering" (performed with high-temperature solder containing up to 40% silver) is also often a form of brazing, since it involves filler materials with melting points in the vicinity of, or in excess of, 450 C. Although the term "silver soldering" is used much more often than "silver brazing", it may be technically incorrect depending on the exact melting point of the filler in use. In silver soldering ("hard soldering"), the goal is generally to give a beautiful, structurally sound joint, especially in the field of jewelry. Thus, the temperatures involved, and the usual use of a torch rather than an iron, would seem to indicate that the process should be referred to as "brazing" rather than "soldering", but the endurance of the "soldering" apellation serves to indicate the arbitrary nature of the distinction (and the level of confusion) between the two processes.Induction soldering is a process which is similar to brazing. The source of heat in induction soldering is induction heating by high-frequency AC current. Generally copper coils are used for the induction heating. This induces currents in the part being soldered. The coils are usually made of copper or a copper base alloy. The copper rings can be made to fit the part needed to be soldered for precision in the work piece. Induction soldering is a process in which a filler metal (solder) is placed between the faying surfaces of (to be joined) metals. The filler metal in this process is melted at a fairly low temperature. Fluxes are a common use in induction soldering. This is a process which is particularly suitable for soldering continuously. The process is usually done with coils that wrap around a cylinder/pipe that needs to be soldered. Some metals are easier to solder than others. Copper, silver, and gold are easy. Iron and nickel are found to be more difficult. Because of their thin, strong oxide films, stainless steel and aluminum are a little more difficult. Titanium, magnesium, cast irons, steels, ceramics, and graphites can be soldered but it involves a process similar to joining carbides. They are first plated with a suitable metallic element that induces interfacial bonding.DESOLDERING AND RESOLDERINGUsed solder contains some of the dissolved base metals and is unsuitable for reuse in making new joints. Once the solder's capacity for the base metal has been achieved it will no longer properly bond with the base metal, usually resulting in a brittle cold solder joint with a crystalline appearance.It is good practice to remove solder from a joint prior to resolderingdesoldering braids or vacuum desoldering equipment (solder suckers) can be used. Desoldering wicks contain plenty of flux that will lift the contamination from the copper trace and any device leads that are present. This will leave a bright, shiny, clean junction to be resoldered.The lower melting point of solder means it can be melted away from the base metal, leaving it mostly intact though the outer layer will be "tinned" with solder. Flux will remain which can easily be removed by abrasive or chemical processes. This tinned layer will allow solder to flow into a new joint, resulting in a new joint, as well as making the new solder flow very quickly and easily.Common toolsHand-soldering tools include the electric soldering iron, which has a variety of tips available ranging from blunt to very fine to chisel heads for hot-cutting plastics, and the soldering gun, which typically provides more power, giving faster heat-up and allowing larger parts to be soldered. Hot-air guns and pencils allow rework of component packages which cannot easily be performed with irons and guns.Soldering torches are a type of soldering device that uses a flame rather than a soldering iron tip to heat solder. Soldering torches are often powered by butane[3] and are available in sizes ranging from very small butane/oxygen units suitable for very fine but high-temperature jewelry work, to full-size oxy-fuel torches suitable for much larger work such as copper piping.A soldering copper is a tool with a large copper head and a long handle, which is heated in a blacksmith's forge fire, and used to apply heat to sheet metal for soldering. Soldering coppers are sometimes used in auto bodywork, although body solder has been mostly superseded by non-metallic fillers.Toaster ovens and hand held infrared lights have been used to reproduce production processes on a much smaller scale.Bristle brushes are usually used to apply plumbing paste flux. For electronic work, flux-core solder is generally used, but additional flux may be used from a flux pen or dispensed from a small bottle with a syringe-like needle.Wire brush, wire wool and emery cloth are commonly used to prepare plumbing joints for connection. Electronic joints rarely require mechanical cleaning.For PCB assembly and rework, alcohol and acetone are commonly used with cotton swabs or bristle brushes to remove flux residue. A heavy rag is usually used to remove flux from a plumbing joint before it cools and hardens. A fiberglass brush can also be used.For electronic work, solder wick and vacuum-operated "solder sucker" are used to undo solder connections.A heat sink, such as a crocodile clips, can also be used to prevent damaging heat-sensitive components while soldering.

SOLDERING TOOLSThe only tools that are essential to solder are a soldering iron and some solder. There are, however, lots of soldering accessories available (see soldering accessories for more information).Different soldering jobs will need different tools, and different temperatures too. For circuit board work you will need a finer tip, a lower temperature and finer grade solder. You may also want to use a magnifying glass. Audio connectors such as XLR's will require a larger tip, higher temperature and thicker solder. Clamps and holders are also handy when soldering audio cables.Soldering IronsThere are several things to consider when choosing a soldering iron. Wattage adjustable or fixed temperature power source (electric or gas) portable or bench use I do not recommend soldering guns, as these have no temperature control and can get too hot. This can result in damage to circuit boards, melt cable insulation, and even damage connectors.WattageIt is important to realise that higher wattage does not necessarily mean hotter soldering iron. Higher wattage irons just have more power available to cope with bigger joints. A low wattage iron may not keep its temperature on a big joint, as it can loose heat faster than it can reheat itself. Therefore, smaller joints such as circuit boards require a lesser wattage iron - around 15-30 watts will be fine. Audio connectors need something bigger - I recommend 40 watts at least.TemperatureThere are a lot of cheap, low watt irons with no temperature control available. Most of these are fine for basic soldering, but if you are going to be doing a lot you may want to consider a variable temperature soldering iron. Some of these simply have a boost button on the handle, which is useful with larger joints, others have a thermostatic control so you can vary the heat of the tip.If you have a temperature controlled iron you should start at about 315-345C (600-650F). You may want to increase this however - I prefer about 700-750F. Use a temperature that will allow you to complete a joint in 1 to 3 seconds.PowerMost soldering irons are mains powered - either 110/230v AC, or benchtop soldering stations which transform down to low voltage DC. Also available are battery and gas powered. These are great for the toolbox, but you'll want a plug in one for your bench. Gas soldering irons loose their heat in windy outside conditions more easily that a good high wattage mains powered iron.PortabilityMost cheaper soldering irons will need to plug into the mains. This is fine a lot of the time, but if there is no mains socket around, you will need another solution. Gas and battery soldering irons are the answer here. They are totally portable and can be taken and used almost anywhere. They may not be as efficient at heating as a good high wattage iron, but they can get you out of a lot of hassle at times. If you have a bench setup, you should consider using a soldering station. These usually have a soldering iron and desoldering iron with heatproof stands, variable heat, and a place for a cleaning pad. A good solder station will be reliable, accurate with its temperature, and with a range of tips handy it can perform any soldering task you attempt with it.SolderThe most commonly used type of solder is rosin core. The rosin is flux, which cleans as you solder. The other type of solder is acid core and unless you are experienced at soldering, you should stick to rosin core solder. Acid core solder can be tricky, and better avoided for the beginner. Rosin core solder comes in three main types - 50/50, 60/40 and 63/37. These numbers represent the amount of tin and lead are present in the solder,as shown below.Solder Type% Tin% LeadMelting Temp (F)

50/505050425

60/406040371

63/376337361

Any general purpose rosin core solder will be fine.SOLDERING ACCESSORIESSoldering Iron TipsTry to use the right size tip whenever you can. Smaller wires and circuit boards require small fine tips, and mic cable onto an XLR would need a larger tip. You can get pointed tips, or flat tipped ones (sometimes called 'spade tips'). If you have a solder station with a desolderer, you will also want a range of desoldering tips and cleaners.Soldering Iron StandsThese are handy to use if you are doing several or more joints. It is a heat resistant cradle for your iron to sit in, so you don't have to lie it down on the bench while it is hot. It really is essential if you are planning to do a lot of bench soldering as it is only a matter of time before you burn something (probably your elbow resting on the hot tip) if you don't use one.ClampsI strongly recommend clamps of some sort. Trying to hold your soldering iron, the solder, and the wire is tricky enough, but when you have to hold the connector as well it is almost impossible. The are however, adjustable clamps that can be manipulated to hold both the connector and the wire in place so you still have two free hands to apply the heat and the solder. These are cheap items, and I know mine have paid for themselves many times over.Magnifying glassIf you are doing work on PCBs (printed circuit boards) you may need to get a magnifying glass. This will help you see the tracks on the PCB, and unless you have exceptional sight, small chip resistors are pretty difficult to solder on well without a magnifying glass. Once again, they are not expensive, and some clamps come with one that can mount on the clamp stand.Solder WickSolder wick is a mesh the you lie on a joint and heat. When it heats up it also melts the solder which is drawn out of the joint. It is usually used for cleaning up solder from tracks on a circuit board, but you will need a solder sucker to clean out the holes in the circuit board. Place the wick on the solder you want to remove then put your soldering iron on top of the wick. The wick will heat up, then the solder will melt and flow away from the joint and into wick.Solder SuckersIf you don't have a solder station with desolderer, and you work on PCB's, you are going to need one of these before too long. They are spring loaded and suck the melted solder out of the joint. They are a bit tricky to use, as you have to melt the solder with your iron, then quickly position the solder sucker over the melted solder and release the spring to suck up the solder. I find solder wick to be easier to use and more effective.Fume ExtractorsSolder fumes are poisonous. A fume extractor will suck the fumes (smoke) into itself and filter it. An absolute must for your health if you are setting up a soldering bench.PREPARATIONStep 1: PreparationIf you are preparing the cable for a connector, I strongly suggest you put any connector parts on now (the screw on part of an XLR, or casing of a 1/4" jack for example). Get into the habit of sliding these on before you start on the cable, or else you can bet it won't be long before you finish soldering your connector only to discover you forgot to put the connector casing on, and have to start all over again.Once you have all the connector parts on that you need, you will need to strip your cable. This means removing the insulation from the end of the wire and exposing the copper core. You can either use a wire stripper, side cutters, or a knife to do this. The obvious tool to choose to strip a wire would be......a wire stripper. There are many types of wire stripper, and most of them work the same. You simply put the wire in, and squeeze it and pull the end bit off. It will cut to a preset depth, and if you have chosen the right depth it will cut the insulation off perfectly. It is possible to choose the wrong depth and cut too deeply, or too shallow, but they are very easy to use.On the other hand, some people (myself included) prefer to use a knife or side cutters. I use side cutters for small cable and a Stanley knife for bigger cables...and although I have a couple of wire strippers, I haven't used them for years. This may seem odd, but I've got my side cutters and knife with me anyway, and they do the job fine.If you are using side cutters (as shown here), position them about 10mm (1/2 inch) from the end, and gently squeeze the cutters into the insulation to pierce it, but not far enough to cut the copper strands of the core. Open the cutters slightly so you can turn the wire and pierce the rest of the insulation. You may have to do this a few times to cut through all of the insulation, but it is better to cut too shallow and have to turn and cut again rather than cut the core and have to start again. Now you should be able to slide the insulation off with your cutters, or pull it off with your fingers. This may sound a tedious method, but in no time at all you will be able to do it in two cuts and a flick of the cutters.I won't explain how I use a knife to do larger cable, as I'd hate someone to slice a finger or thumb open following my instructions. Using a sharp blade like that certainly does have it's risks, so stick with wire cutters or side cutters if you are at all unsure.If your connector has been used before, make sure you remove any remnants of wire and solder from the contacts. Do this by putting the tip of your soldering iron into the hole and flicking the solder out when it has melted. Common Sense Alert! Please be careful when you flick melted solder...flick it away from you.TINNINGStep 2: TinningWhatever it is you are soldering, you should 'tin' both contacts before you attempt to solder them. This coats or fills the wires or connector contacts with solder so you can easily melt them together.To tin a wire, apply the tip of your iron to the wire for a second or two, then apply the solder to the wire. The solder should flow freely onto the wire and coat it (if it's stranded wire the solder should flow into it, and fill the wire). You may need to snip the end off afterwards, particularly if you have put a little too much solder on and it has formed a little ball at the end of the wire.Be careful not to overheat the wire, as the insulation will start to melt. On cheaper cable the insulation can 'shrink back' if heated too much, and expose more copper core that you intended. You can cut the wire back after you have tinned it, but it's best simply not to over heat it.The larger the copper core, the longer it will take to heat up enough to draw the solder in, so use a higher temperature soldering iron for larger cables if you can.To tin a contact on an audio XLR connector, hold the iron on the outside of the the contact for a second or two, then apply the solder into the cavity of the contact. Once again, the solder should flow freely and fill the contact. Connectors such as jacks have contacts that are just holes in a flat part of the connector. To tin these you put your iron on it, and apply the solder to where the iron is touching. The solder should flow and cover the hole.Once you have tinned both parts, you are ready to solder them together.

SOLDERINGStep 3: SolderingThis step can often be the easiest when soldering audio cables.You simply need to place your soldering iron onto the contact to melt the solder.When the solder in the contact melts, slide the wire into the contact.Remove the iron and hold the wire still while the solder solidifies again.You will see the solder 'set' as it goes hard.This should all take around 1-3 seconds. A good solder joint will be smooth and shiny. If the joint is dull and crinkly, the wire probably moved during soldering. If you have taken too long it will have have solder spikes. If it does not go so well, you may find the insulation has melted, or there is too much stripped wire showing. If this is the case, you should desolder the joint and start again.

CLEANING YOUR SOLDERING IRONYou should clean your tip after each use. There are many cleaning solutions and the cheapest (and some say best) is a damp sponge. Just rub the soldering iron tip on it after each solder.Another option is to use tip cleaner. This comes in a little pot that you push the tip into. This works well if your tip hasn't been cleaned for a while. It does create a lot of smoke, so it is better not to let the tip get so dirty that you need to use tip cleaner.Some solder stations come with a little pad at the base of the holder. If you have one of these, you should get into the habit of wiping the tip on the pad each time you apply solder with it.If you need to clean solder off a circuit board, solder wick is what you need. You place the wick on the joint or track you want to clean up, and apply your soldering iron on top. The solder melts and is drawn into the wick. If there is a lot of solder the wick will fill up, so gently pull the wick through the joint and your iron, and the solder will flow into it as it passes.

Tips and Tricks1. Melted solder flows towards heat. 2. Most beginning solderers tend to use too much solder and heat the joint for too long. 3. Don't move the joint until the solder has cooled. 4. Keep your iron tip clean. 5. Use the proper type of iron and tip size. TROUBLESHOOTINGIf either of the parts you are soldering is dirty or greasy, the solder won't take (or 'stick') to it. Desolder the joint and clean the parts before trying again.Another reason the solder won't take is that it may not be the right sort of metal. For example you cannot solder aluminium with lead/tin solder. If the joint has been moved during soldering, it may look grainy or dull. It may also look like this if the joint was not heated properly while soldering.If the joint was overheated the solder will have formed a spike and there will be burnt flux residue.

9. CONCLUSIONBy making the project PROGRAMMABLE SECURITY CODE LOCK in major project for final year I conclude that In this project we put our greatest effort to understand & explore more & more about the project. This project has many useful applications in industries and security systems for all types of applications also. we try our best to make this project successful.

10. BIBLIOGRAPHYI developed my this project report of PROGRAMMABLE SECURITY CODE LOCK from following books and web sites.Electronics and Circuits, by Allen MottersheadBasic Electronics, by Miami A.Kwww.electronicsforu.comwww.wikipedia.comwww.atmel.Comwww.electroschematics.comwww.datasheetarchive.com

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