MAJOR PROJECT REPORT

on

TEMPERATURE SENSOR AND CONTROL EQUIPMENT

Submitted to Punjab Technical University in partial fulfillment of the requirement for the award of

BACHELOR OF TECHNOLOGYIn

ELECTRONICS & INSTRUMENTATION ENGINEERING

Submitted ByRAMANDEEP SINGH

7170610130SURBHI BHANDARI

7170610143

Guided ByMr.AMRJEET SINGH

Mr. VIKAS GOEL

DEPTT. OF ELECTRONICS & INSTRUMENTATION ENGINEERING

INSTITUTE OF ENGINEERING & TECHNOLOGY, BHADDAL

2007-11

CANDIDATE’S DECLARATION

We hereby declare that the major project which is presented in this report entitled

“TEMPERATURE SENSOR AND CONTROL EQUIPMENT” submitted in the

partial fulfillment of the requirements for the award of the degree of Bachelor of

Technology in Electronics & Instrumentation Engineering to the Punjab Technical

University, Jalandhar, is an authentic record of our own work carried out at I.E.T-

Bhaddal campus. The material embodied in this project work has not been

submitted to any other university or institution for the award of any degree.

RAMANDEEP SINGH SURBHI BHAN DARIEI/07/7544 EI/07/75577170610130 7170610143Place: IET BHADDAL ROPAR Date:

This is to certify that above statement made by the candidate(s) is correct to the best of my knowledge.

Guided by:Mr. AMARJEET SINGHDepartment of Electronics & Instrumentation Engineering

Approved by:

H.O.D. (EIE)I.E.T. - Bhaddal

ACKNOWLEDGEMENT

We express our gratitude to the Punjab Technical University, Jalandhar, for giving

us the opportunity to work on the major project during our final year of B. Tech. of

Electronics & Instrumentation Engineering. There are many who helped us during

this project work, and we want to thank them all.

We would like to thank Dr. H.R.Verma, Director-Principal, Institute of Engineering

and Technology, Bhaddal for his kind support. Our special thanks to Mr. Vikas

Goel HOD EIE & our project guide for his invaluable guidance throughout our

project work and endeavor period has provided us with the requisite motivation to

complete our project successfully.

We specially appreciate the help and guidance all those people who have directly or

indirectly helped us making our project a success.

RAMANDEEP SINGH

SURBHI BHANDARI

Table of contents

1. Abstract2. Block diagram3. Block diagram description

Temperature sensorADCMicrocontrollerLCDPower Supply

4. Circuit Diagram5. Circuit Description6. List of components7. Working8. Software tools9. Results and conclusions10. References

List of figures and tablesFigure 1: Block diagramFigure 2: Circuit diagram

Table 1: List of components

ABSTRACT:-

Measuring the impact of environmental Constraints is Important for proper data Analysis and control. Different types of data loggers and data acquisition systems are available in the market to perform this task well.

Temperature measurement is today more common. The ambient temperature keeps varying during different times of the day and night at different places. Temperature measurement can be done for weather forecast or for automation in electronics devices and industries.

Here we describe a temperature measurement device which uses microcontroller AT89C51, temperature sensor and other components. The temperature is measured at a user-defined interval. Each time the current temperature goes above the user-defined threshold value, the buzzer sounds.

BLOCK DIAGRAM:-

BLOCK DESCRIPTION:-

1. Temperature Sensor: - The LM35 series are precision integrated-circuit temperature sensors, whose output voltage is linearly proportional to the Celsius (Centigrade) temperature. It is used to sense the temperature.

2. Analog to Digital Converter :- An analog-to-digital converter (abbreviated ADC, A/D or A to D) is a device which converts the sensed analog signal to digital signal.The ADC0804 is CMOS 8-bit successive approximation A/D converters that use a differential potentiometric ladder-similar to the 256R products. These converters are designed to allow operation with the NSC800 and INS8080A derivative control bus with TRI-STATE output latches directly driving the data bus. These A/Ds appear like memory locations or I/O ports to the microprocessor and no interfacing logic is needed.

3. Microcontroller: - The AT89S51 is a low-power, high-performance CMOS 8-bit microcontroller with 4K bytes of In-System Programmable Flash memory. The device is manufactured using Atmel’s high-density nonvolatile memory technology and is compatible with the industryStandard 80C51 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 In-System Programmable

Flash on a monolithic chip, the Atmel AT89S51 is a powerful microcontroller

which provides a highly-flexible and cost-effective solution to many embedded control applications.

The AT89S51 provides the following standard features: 4K bytes of Flash, 128 bytes of RAM, 32 I/O lines, Watchdog timer, two data pointers, 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 AT89S51 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 external interrupt or hardware reset.

4. LCD MODULE:- The output is taken over the LCD screen.

CIRCUIT DIAGRAM:-

CIRCUIT DESCRIPTION:-

Fig. 1 shows the circuit of the microcontroller- based temperature meter. It comprises microcontroller AT89C51, temperature sensor LM35, analogue to- digital converter ADC0804, voltage regulator 7805 (Fig. 2), an LCD module and a few discrete components.

The AT89C51 is a low-power, high-performance CMOS 8-bit microcomputer with 4 kB of Flash programmable and erasable read only memory (PEROM). It provides the following standard features: 4 kB of flash, 128 bytes of RAM, 32 input/output (I/O) lines, two 16-bit timer/ counters, five-vector two-level interrupt architecture, a full-duplex serial port, and 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, timers/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.

An 11.0592MH2 crystal is connected to pins 18 and 19 to provide basic clock to the microcontroller. Capacitors C4 and C5 connected in parallel to the crystal maintain the resonance. Switch S1 is used to manually reset the microcontroller, while the power-on reset signal for the microcontroller is derived from the combination of capacitor C3 and resistor R2.

IC LM35 (IC3) is a three-terminal, precision temperature sensor whose output voltage is linearly proportional to the Celsius temperature with 110.0 mV/"C scale factor. It thus has an advantage over linear temperature sensors calibrated in °Kelvin, as the user is not required to subtract a large constant voltage from its output to obtain convenient Centigrade scaling.

The LM35 does not require any external calibration or trimming to provide typical accuracies. It is rated for full -55oC to 150.C range and operates off 4V-30V input. It gives 0V output for 0°C temperature. The analogue output (Vout) at pin 2 of LM35 is fed to Vin (+) pin 6 of analogue-to-digital converter ADC0804, whose V,, (-) plr:r7 is connected to ground. Pin 1 of LM35 is connected to 5V supply and pin 3 is grounded.

ADC0804 (IC2) is a CMOS, 8-bit, single-channel analogue-to-digital converter. It features conversion time of less than 100 ms, differential analogue input voltage, TTL-compatible inputs and outputs, on-chip clock generator, analogue voltage input range

from 0V to 5V, and no zero adjustment. The conversion time depends on resistor R3 and capacitor C6. The conversion rate in free-running mode is 640 kHz. Digital and analogue ground should be separated in ADC0804 to avoid any interference in the circuit.

The resolution of 8-bit ADC0804 is 19.53 mV, which doesn't match with the scale factor of LM3S and therefore can cause error. To avoid this error, the full-scale range of ADC0804 is made 0-256V by adjusting the voltage at pin 9 (Vret/2) to 1.28V through1-kilo-ohm preset VR2. In ADC0804, the input analogue voltage is divided by its step size to give digital output. For each 10mV rise and fall of the analogue input at Vin (+), digital outputs at DBO throughDB7 increase and decrease respectively. The maximum input voltage that can be converted by the ADC is 2.55V (10mV x 2SS) giving full-scale output of FF hex value in this system.

The 8-bit digital output of ADC0804 (DB0 through DB7) is connected to 8-bit port p0 of the microcontroller. Signals RD, WR and INTR of the ADC are connected to P27, P2.6 and P2.5 of the microcontroller. These signals of the ADC act as handshaking signals with microcontroller IC1.RD and WR are the input pins of the ADC, while INTR is the output pin. Through INTR signal, the microcontroller gets to know when the conversion from analogue into digital is completed by the ADC.The microcontroller makes WR Pin 'low' and RD pin 'high' to start the conversion. Pin INTR goes high for the end of conversion. A transition from high to low on INTR indicates end of conversion. Then the microcontroller makes RD 'low' and WR 'high' to read the 8-bit data at DBO through DB7 through microcontroller port P0. Through its firmware, the microcontroller multiplies the digital input at port 0 with the step size value of ADC0804 and then divides with the temperature/volt scale factor of LM35 to give the measured and calibrated ºC temperature.The measured temperature is instantaneously displayed on the LCD. Port Pl, of the microcontroller is connected to data port pins 7 through 14 of the LCD module. The handshake signals of the LCD (RS, R/W and Enable) are connected to P3.2, P3.3 and.P3.4 of the microcontroller, respectively. All the data is sent to the LCD in ASCII form to display. Only the commands are sent in hex form to the LCD. RS signal is used to distinguish between data (RS=1) and command (RS=O). Use Preset VR1 to control the contrast of the LCD.

Switches S2, S3 and S4 connected to pins P2.2, P2.1 and P2.0 are treated as ‘Up’, 'down' and enter, buttons, respectively by the temperature setting of the microcontroller. Measuring interval and threshold temperature values are to be entered by the user using switches S2, S3 and S4 whenever the microcontroller starts. The range of measuring interval is 1 second to 99 seconds.According to this measuring interval, the microcontroller measures the temperature value in its flash memory. Whenever the measured temperature rises above the threshold value, the piezoelectric buzzer at pin P2.4 sounds until the temperature becomes lower than these threshold value.Time between measurements of two temperature samples is treated as waiting time measuring interval. So during waiting time, LED2 connected at pin P2.3 of the

microcontroller glows. It is turned off during measurement. Resistor R4 acts as the current limiter for LED2.

Fig 2: Power Supply Circuit

Fig. 2 shows the power supply circuit. The 230V, 50 Hz AC mains is stepped down by transformer X1 to deliver secondary output of 9V 500mA.The transformer output is rectified by a full-wave rectifier comprising diodes D1 through D4, filtered by capacitor C1 and regulated by IC LM7805 to provide +5V DC output. Capacitor C2 provides further filtering. LED1 indicates DC power and R1 acts as the current limiter.

List of components:-

S.No.

Code Name Value Price

1. R1,R4R2,R3,R5-R8Resistor n/wVR1-VR2

Resistors 330 ohms10k10k10k

25 paisa each

2. C4,C5C6C2C3C1

Capacitors 33Pf150pF0.1µF10µF1000µF

1

13

3. IC1IC2IC3IC4D1-D4LED1,LED2

MicrocontrollerADCTemp. sensorRegulatorDiodeLED

AT89S51ADC0804LM35LM78051N40075mm

5020

1011

4. X1 Transformer 230V,500mA 50

XtalLCDPZ1

CrystalLCD ModulePiezobuzzer

12MHz16*2 line

10

Construction and testing:-

An actual-size, single-side PCB for the microcontroller-based temperature meter is shown in Fig. below and its component layout Wire the circuit on the PCB. Use bases for ICs AT89C51 and ADC0804 program the ATS9C51 with suitable programmer and put into the IC base after soldering all the components and checking +5V at each Vcc point of the circuit. Also check continuity between respective connections using a multimeter.

For proper measurement, adjust preset VR2 to give 1.28V at pin 9 of the ADC. Initially, using preset VR1, set the contrast level for proper Display on the LCD. If the reading on the display is not steady, check for loose connections or dry soldering joints.

An actual-size, single-side PCB for the microcontroller-based temperature meter

Component layout for the PCB

SOFTWARE:-

The software is well commented and easy to understand. Written inAssembly language and assembled using A51 assembler, it works as per the flow-chart shown in Fig. 5.Assembler directives and comments are used for proper understanding of the software. The hex code generated by the assembler is burnt into the microcontroller using a suitable programmer.The ranges for measuring time interval (01 to 99 seconds) and threshold temperature value (20.C to 49oC) are set by the software. The values of the measured temperature and the number of samples taken until power-on, are displayed on the LCD screen as shown in Fig. 6. The number of samples is updated according to the measuring interval.

LCD Screen

Each port of the microcontroller is made input through software by putting high on the respective pin or port. By default, all the ports act as outputs. Instead of using timer, nested loops are used to provide delays at various locations of the software. The values for the loops are calculated according to the crystal frequency and the machine cycles taken by the used instructions. Functioning of all the keys (up, down and enter) is also handled by the software. Pooling, identification of keys, and limits for up and down are provided by the software.

SOFTWARE TOOLS:-

Orcad for circuit designing .We first make schematic in it. This in turn creates lay out of PCB.

Keil for compiling. Microcontroller understands hex files. But as hex files are very complicated therefore we make use of the software keil. Programming in keil makes use of C or Assembly language which are easily programmable. Keil on its own converts these files to hex files.

Proload After the formation of hex file we need to insert this hex file into the micro controller so that it executes the program written in the keil. For this purpose we make use of proload.

Soldering

Soldering 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 400 °C (800 °F). 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.

Applications

One 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.

Solders

Soldering 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 183–190 °C (361–374 °F) 50/50: melts between 185–215 °C (365–419 °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.

Flux

In 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 techniques

Methods

Soldering 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 processes—brazing 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 resoldering

Used 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 resoldering—desoldering 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 tools

Hand-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 Tools

The 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 Irons

There 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.

Wattage

It 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.

Temperature

There 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 315-345°C (600-650°F). You may want to increase this however - I prefer about 700-750°F. Use a temperature that will allow you to complete a joint in 1 to 3 seconds.

Power

Most 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.

Portability

Most 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.

 

Solder

The 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 % Lead Melting Temp (°F)

50/50 50 50 425

60/40 60 40 371

63/37 63 37 361

Any general purpose rosin core solder will be fine.

Soldering Accessories

Soldering Iron Tips

Try 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 Stands

These 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.

Clamps

I 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 glass

If 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 Wick

Solder 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 Suckers

If 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 Extractors

Solder 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.

Preparation

Step 1: Preparation

If 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.

Tinning

Step 2: Tinning

Whatever 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.

Soldering

Step 3: Soldering

This 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 Iron

You 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.

Troubleshooting

If 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.

Power supply

The term power supply is more commonly abbreviated to PSU, this will be used from hereon in.

Telecommunications equipment is designed to operate on voltages lower than the domestic Mains voltage. In order to reduce this voltage a PSU is used.

To provide a useable low voltage the PSU needs to do a number of things:-

Reduce the Mains AC (Alternating current) voltage to a lower level. Convert this lower voltage from AC to DC (Direct current)

Regulate the DC output to compensate for varying load (current demand)

Provide protection against excessive input/output voltages.

Reduction of AC MainsThis is achieved by using a device known as a Transformer an electromagnetic device consisting of an ferrous iron core which has a large number of turns of wire wound around it, known as the Primary Winding

The ends of these turns of wire being connected to the input voltage (in this case Mains AC).

A second number of turns of wire are wound around the Primary Winding, this set being known as the Secondary Winding.

The difference between the number of turns provides us with a way of reducing (in our case) a high AC voltage to a lower one.

Conversion of AC to DCTo convert our now low AC voltage to DC we use a Rectifier Diode connected to the Secondary Winding.

This is a silicon diode, which has operation analogous to a bicycle tyre valve (as the valve only allows air to flow into the tyre, the diode only allows current to flow in one direction)

As our low AC voltage will be working at a frequency of 50Hz (Mains AC frequency) it is desirable to reduce the inherent hum on this to a lower level.

This is achieved by a technique known as Smoothing (“Ironing” out the bumps in the AC).

A simple way to reduce the hum is to use Full Wave Rectification.

Today this is usually done by four diodes in a bridge configuration known as a Bridge Rectifier. (This can be four individual diodes or a dedicated self contained package)

Regulation of Output VoltageThe Electrolytic Capacitor is a device capable of storing energy the amount of energy and the time it remains stored depending on the value.

In a simple PSU the easiest way to provide regulation to compensate for varying load conditions is to use a pair of relatively high value Electrolytic Capacitors.

Their values in this case being in the region of 470uF to 2000uF depending on the application and the amount of current required from the output of the unit.

One of these capacitors is connected across the DC output of the rectifier diode(s) or bridge, this capacitor also providing an extra degree of smoothing the output waveform.

The second capacitor is connected via a low value, medium to high wattage resistor, which assists in limiting the current demand.

Protection against excessive voltages In a simple PSU the easiest way to do this is by providing fuses at the input to the transformer, generally in the live side of the mains supply, also at the DC outputs.

In the event of an excessive input voltage, or excessive current being drawn from the output, one of these fuses should normally blow protecting the PSU and the equipment connected to it.

The transformer may also be fitted with an internal or external thermal fuse, which will open if the transformer becomes hot due to the aforementioned conditions.

Transformers

A "transformer" takes one voltage and changes it into another.

What is a transformer, and why should I care?

A "transformer" changes one voltage to another. This attribute is useful in many ways.

A transformer doesn't change power levels. If you put 100 Watts into a transformer, 100 Watts come out the other end. [Actually, there are minor losses in the transformer because nothing in the real world is 100% perfect. But transformers come pretty darn close; perhaps 95% efficient.]

A transformer is made from two coils of wire close to each other (sometimes wrapped around an iron or ferrite "core"). Power is fed into one coil (the "primary"), which creates a magnetic field. The magnetic field causes current to flow in the other coil (the "secondary"). Note that this doesn't work for direct current (DC): the incoming voltage needs to change over time - alternating current (AC) or pulsed DC.

Iron core

The number of times the wires are wrapped around the core ("turns") is very important and determines how the transformer changes the voltage.

If the primary has fewer turns than the secondary, you have a step-up transformer that increases the voltage.

If the primary has more turns than the secondary, you have a step-down transformer that reduces the voltage.

If the primary has the same number of turns as the secondary, the outgoing voltage will be the same as what comes in. This is the case for an isolation transformer.

In certain exceptional cases, one large coil of wire can serve as both primary and secondary. This is the case with variable auto-transformers and xenon strobe trigger transformers.

 Types of transformersIn general, transformers are used for two purposes: signal matching and power supplies.

 Power TransformersPower transformers are used to convert from one voltage to another, at significant power levels.

 

Step-up transformers

A "step-up transformer" allows a device that requires a high voltage power supply to operate from a lower voltage source. The transformer takes in the low voltage at a high current and puts out the high voltage at a low current.

Examples:

You are a Swiss visiting the U.S.A., and want to operate your 220VAC shaver off of the available 110 VAC.

The CRT display tube of your computer monitor requires thousands of volts, but must run off of 220 VAC from the wall.

 Step-down transformers

A "step-down transformer" allows a device that requires a low voltage power supply to operate from a higher voltage. The transformer takes in the high voltage at a low current and puts out a low voltage at a high current.

Examples:

Your Mailbu-brand landscape lights run on 12VAC, but you plug them into the 220 VAC line.

Your doorbell doesn't need batteries. It runs on 220 VAC, converted to 12VAC.

In many cases, step-down transformers take the form of wall warts.

 

Isolation transformers

An "isolation transformer" does not raise or lower a voltage; whatever voltage comes in is what goes out. An isolation transformer prevents current from flowing directly from one side to the other. This usually serves as a safety device to prevent electrocution.  

Variable auto-transformers

A "variable auto-transformer" (variac) can act like a step-up transformer or step-down transformer. It has a big knob on top that allows you to dial in whatever output voltage you want.

This page from the All Electronics catalog (#103, Winter 2003) shows some variacs.

WARNING: A variable auto-transformer does not provide isolation from line current. For that you need an isolation transformer.

 InvertersAn "inverter" takes a DC power source and boosts it up to a higher voltage. The most common type of inverter takes power from an automobile and cranks out 220 VAC to run appliances and power tools. Inverters are also used to operate fluorescent lamps from battery power.

Technically, an inverter isn't a transformer; it contains a transformer (and lots of other stuff).

 Signal Transformers"Signal transformers" also take one thing in and transform it to another thing out. But in this case, the power levels are low, and the transformed thing carries some type of information signal.

In most cases, these transformers are thought of as impedance matching.

 

Rectifier

What is a Rectifier?

A rectifier changes alternating current into direct current. This process is called rectification. The three main types of rectifier are the half-wave, full-wave, and bridge. A rectifier is the opposite of an inverter, which changes direct current into alternating current.

Half-Wave Rectifier

The simplest type is the half-wave rectifier, which can be made with just one diode. When the voltage of the alternating current is positive, the diode becomes forward-biased and current flows through it. When the voltage is negative, the diode is reverse-biased and the current stops. The result is a clipped copy of the alternating current waveform

with only positive voltage, and an average voltage that is one third of the peak input voltage. This pulsating direct current is adequate for some components, but others require a more steady current. This requires a full-wave rectifier that can convert both parts of the cycle to positive voltage.

Full-Wave Rectifier

The full-wave rectifier is essentially two half-wave rectifiers, and can be made with two diodes and an earthed center tap on the transformer. The positive voltage half of the cycle flows through one diode, and the negative half flows through the other. The center tap allows the circuit to be completed because current can not flow through the other diode. The result is still a pulsating direct current but with just over half the input peak voltage, and double the frequency.

Bridge Rectifier

The bridge rectifier, also called a diode bridge, consists of four diodes connected together in a square. Two diodes are connected at their anodes, and the other two are connected at their cathodes. These form the rectified output terminals. The remaining ends are joined to form two input terminals. It it usually packaged as one component with four terminals. The bridge rectifier allows for full-wave rectification without the need for an earthed center tap on the transformer.

Smoothing

Even the bridge rectifier has some variation in it's output voltage, so a filter is required to smooth out this ripple. A capacitor connected across the output terminals acts as a basic filter by storing energy during the peak voltage, and releasing it when the voltage falls. This removes most of the ripple but does not result in a steady voltage. A choke and second capacitor are usually added to further smooth the ripple.

Rectifier Uses

Rectifiers are used mostly in power adapters and alternators to convert alternating current to direct current. They are also used in radios to demodulate signals from the antenna.

COMPONENTS

Resistors

Example:       Circuit symbol:   

Function

Resistors 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.

Connecting and soldering

Resistors may be connected either way round. They are not damaged by heat when

soldering.

Resistor values - the resistor colour code

Resistance is measured in ohms, the symbol for ohm is an omega .

1 is quite small so resistor values are often given in k and M .

1 k = 1000     1 M = 1000000 .

Resistor values are normally shown using coloured bands.

Each colour represents a number as shown in the table.

Most resistors have 4 bands:

The first band gives the first digit.

The second band gives the second digit.

The third band indicates the number of zeros.

The fourth band is used to shows the tolerance (precision) of the resistor, this may

be ignored for almost all circuits but further details are given below.

The Resistor

Colour Code

Colour Number

Black 0

Brown 1

Red 2

Orange 3

Yellow 4

Green 5

Blue 6

Violet 7

Grey 8

White 9

This resistor has red (2), violet (7), yellow (4 zeros) and gold bands.

So its value is 270000 = 270 k .

On circuit diagrams the is usually omitted and the value is written 270K.

Small value resistors (less than 10 ohm)

The standard colour code cannot show values of less than 10 . To show these small

values two special colours are used for the third band: gold which means × 0.1 and

silver which means × 0.01. The first and second bands represent the digits as normal.

For example:

red, violet, gold bands represent 27 × 0.1 = 2.7 

green, blue, silver bands represent 56 × 0.01 = 0.56 

Tolerance of resistors (fourth band of colour code)

The tolerance of a resistor is shown by the fourth band of the colour code. Tolerance is

the precision of the resistor and it is given as a percentage. For example a 390 resistor

with a tolerance of ±10% will have a value within 10% of 390 , between 390 - 39 = 351

and 390 + 39 = 429 (39 is 10% of 390).

A special colour code is used for the fourth band tolerance:

silver ±10%,   gold ±5%,   red ±2%,   brown ±1%.

If no fourth band is shown the tolerance is ±20%.

Tolerance may be ignored for almost all circuits because precise resistor values are rarely

required.

Resistor shorthand:

Resistor values are often written on circuit diagrams using a code system which avoids

using a decimal point because it is easy to miss the small dot. Instead the letters R, K and

M are used in place of the decimal point. To read the code: replace the letter with a

decimal point, then multiply the value by 1000 if the letter was K, or 1000000 if the letter

was M. The letter R means multiply by 1.

For example:

560R means 560

2K7  means 2.7 k = 2700

39K  means 39 k

1M0  means 1.0 M = 1000 k

Resistors in Series and Parallel:

Power Ratings of Resistors

Electrical energy is converted to heat when current flows through

a resistor. Usually the effect is negligible, but if the resistance is

low (or the voltage across the resistor high) a large current may

pass making the resistor become noticeably warm. The resistor

must be able to withstand the heating effect and resistors have

power ratings to show this.

Power ratings of resistors are rarely quoted in parts lists because

for most circuits the standard power ratings of 0.25W or 0.5W are High power resistors

(5W top, 25W bottom)

suitable. For the rare cases where a higher power is required it should be clearly specified

in the parts list, these will be circuits using low value resistors (less than about 300 ) or

high voltages (more than 15V).

The power, P, developed in a resistor is given by:

P = I² × R

or

P = V² / R

where: P = power developed in the resistor in watts (W)

I  = current through the resistor in amps (A)

R = resistance of the resistor in ohms ( )

V = voltage across the resistor in volts (V)

Examples:

A 470 resistor with 10V across it, needs a power rating P = V²/R = 10²/470 =

0.21W.

In this case a standard 0.25W resistor would be suitable.

A 27 resistor with 10V across it, needs a power rating P = V²/R = 10²/27 = 3.7W.

A high power resistor with a rating of 5W would be suitable.

Variable Resistors

Construction

Variable resistors consist of a resistance track with connections

at both ends and a wiper which moves along the track as you

turn the spindle. The track may be made from carbon, cermet

(ceramic and metal mixture) or a coil of wire (for low

resistances). The track is usually rotary but straight track

versions, usually called sliders, are also available.

Variable resistors may be used as a rheostat with two connections (the wiper and just one

end of the track) or as a potentiometer with all three connections in use. Miniature

versions called presets are made for setting up circuits which will not require further

adjustment.

Variable resistors are often called potentiometers in books and catalogues. They are

specified by their maximum resistance, linear or logarithmic track, and their physical

size. The standard spindle diameter is 6mm.

The resistance and type of track are marked on the body:

 4K7 LIN means 4.7 k linear track. 1M LOG means 1 M logarithmic track.

Standard Variable Resistor

Some variable resistors are designed to be mounted directly on the circuit board, but most

are for mounting through a hole drilled in the case containing the circuit with stranded

wire connecting

their terminals to the circuit board.

Resistor color code

Example 1

(Brown=1),(Black=0),(Orange=3)

10 x 103 = 10k ohm

Tolerance(Gold) = ±5%

Example 2

(Yellow=4),(Violet=7),(Black=0),(Red=2)

470 x 102 = 47k ohm

Tolerance(Brown) = ±1%

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 eachother, 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.

When a circuit tester, such as an analog meter

set to measure resistance, is connected to a 10 microfarad (µF) electrolytic capacitor, a

current will flow, but only for a moment. You can confirm that the meter's needle

moves off of zero, but returns to zero right away.

When you connect the meter's probes to the capacitor in reverse, you will note that

current once again flows for a moment. Once again, when the capacitor has fully

charged, the current stops flowing. So the capacitor can be used as a filter that blocks

DC current. (A "DC cut" filter.)

However, in the case of alternating current, the current will be allowed to pass.

Alternating current is similar to repeatedly switching the test meter's probes back and

forth on the capacitor. Current flows every time the probes are switched.

The value of a capacitor (the capacitance), is designated in units called the Farad(F).

The capacitance of a capacitor is generally very small, so units such as the microfarad

( 10-6F ), nanofarad ( 10-9F ), and picofarad (10-12F ) are used.

Recently, an new capacitor with very high capacitance has been developed. The Electric

Double Layer capacitor has capacitance designated in Farad units. These are known as

"Super Capacitors."

Sometimes, a three-digit code is used to indicate the value of a capacitor. There are two

ways in which the capacitance can be written. One uses letters and numbers, the other

uses only numbers. In either case, there are only three characters used. [10n] and [103]

denote the same value of capacitance. The method used differs depending on the

capacitor supplier. In the case that the value is displayed with the three-digit code, the

1st and 2nd digits from the left show the 1st figure and the 2nd figure, and the 3rd digit

is a multiplier which determines how many zeros are to be added to the capacitance.

Picofarad ( pF ) units are written this way.

For example, when the code is [103], it indicates 10 x 103, or 10,000pF = 10

nanofarad( nF ) = 0.01 microfarad( µF ).

If the code happened to be [224], it would be 22 x 104 = or 220,000pF = 220nF =

0.22µF.

Values under 100pF are displayed with 2 digits only. eg, 47 would be 47pF.

The capacitor has an insulator( the dielectric ) between 2 sheets of electrodes. Different

kinds of capacitors use different materials for the dielectric.

Breakdown voltage

When using a capacitor, you must pay attention to the maximum voltage which can be

used. This is the "breakdown voltage." The breakdown voltage depends on the kind of

capacitor being used. You must be especially careful with electrolytic capacitors

because the breakdown voltage is comparatively low. The breakdown voltage of

electrolytic capacitors is displayed as Working Voltage.

The breakdown voltage is the voltage that when exceeded will cause the dielectric

(insulator) inside the capacitor to break down and conduct. When this happens, the

failure can be catastrophic.

Electrolytic Capacitors (Electrochemical type capacitors)

Aluminum is used for the electrodes by using a thin oxidization membrane.

Large values of capacitance can be obtained in comparison with the size of the

capacitor, because the dielectric used is very thin.

The most important characteristic of electrolytic capacitors is that they have polarity.

They have a positive and a

negative electrode

[Polarised]. This means

that it is very important

which way round they are

connected. If the capacitor

is subjected to voltage

exceeding its working

voltage, or if it is

connected with incorrect

polarity, it may burst. It is extremely dangerous, because it can quite literally explode.

Make absolutely no mistakes.

Generally, in the circuit diagram, the positive side is indicated by a "+" (plus) symbol.

Electrolytic capacitors range in value from about 1µF to thousands of µF. Mainly this

type of capacitor is used as a ripple filter in a power supply circuit, or as a filter to

bypass low frequency signals, etc. Because this type of capacitor is comparatively

similar to the nature of a coil in construction, it isn't possible to use for high-frequency

circuits. (It is said that the frequency characteristic is bad.)

The photograph on the left is an example of

the different values of electrolytic capacitors

in which the capacitance and voltage differ.

From the left to right:

1µF (50V) [diameter 5 mm, high 12 mm]

47µF (16V) [diameter 6 mm, high 5 mm]

100µF (25V) [diameter 5 mm, high 11 mm]

220µF (25V) [diameter 8 mm, high 12 mm]

1000µF (50V) [diameter 18 mm, high 40 mm]

The size of the capacitor sometimes depends on the manufacturer. So the

sizes shown here on this page are just examples.

In the photograph to the right, the mark indicating the negative lead of the component

can be seen. You need to pay attention to the polarity indication so as not to make a

mistake when you assemble the circuit.

Ceramic Capacitors

Ceramic capacitors are

constructed with materials such as titanium acid barium used as the dielectric.

Internally, these capacitors are not constructed as a coil, so they can be used in high

frequency applications. Typically, they are used in circuits which bypass high frequency

signals to ground.

These capacitors have the shape of a disk. Their capacitance is comparatively small.

The capacitor on the left is a 100pF capacitor with a diameter of about 3 mm.

The capacitor on the right side is printed with 103, so 10 x 103pF becomes 0.01 µF. The

diameter of the disk is about 6 mm.

Ceramic capacitors have no polarity.

Ceramic capacitors should not be used for analog circuits, because they can distort the

signal.

Multilayer Ceramic Capacitors

The multilayer ceramic capacitor has a many-layered dielectric. These capacitors are

small in size, and have good temperature and frequency characteristics.

Square wave signals used in digital circuits can have a comparatively high

frequency component included.

This capacitor is used to bypass the high frequency to ground.

In the photograph, the capacitance of the

component on the left is displayed as 104. So, the

capacitance is 10 x 104 pF = 0.1 µF. The thickness

is 2 mm, the height is 3 mm, the width is 4

mm.The capacitor to the right has a capacitance of

103 (10 x 103 pF = 0.01 µF). The height is 4 mm,

the diameter of the round part is 2

mm.

These capacitors are not polarized.

That is, they have no polarity.

This capacitor uses thin polyester film

as the dielectric.

They are not high tolerance, but they

are cheap and handy. Their tolerance

is about ±5% to ±10%.

Care must be taken, because different

manufacturers use different methods to denote the capacitance values

0.01 Here are some other polyester film capacitors.

Starting from the left

Capacitance: 0.0047 µF (printed with 472K)

[the width 4mm, the height 6mm, the thickness 2mm]

Capacitance: 0.0068 µF (printed with 682K)

[the width 4mm, the height 6mm, the thickness 2mm] Capacitance: 0.47 µF

(printed with 474K)

[the width 11mm, the height 14mm, the thickness 7mm]

These capacitors have no polarity.

Mica Capacitors

These capacitors use Mica for the

dielectric. Mica capacitors have

good stability because their

temperature coefficient is small.

Because their frequency

characteristic is excellent, they are

used for resonance circuits, and

high frequency filters. Also, they

have good insulation, and so can be utilized in high voltage circuits. It was often used

for vacuum tube style radio transmitters, etc.

Mica capacitors do not have high values of capacitance, and they can be relatively

expensive.

Pictured at the right are "Dipped mica capacitors." These can handle up to 500 volts.

The capacitance from the left

Capacitance: 47pF (printed with 470J)

[the width 7mm, the height 5mm, the thickness 4mm]

Capacitance: 220pF (printed with 221J)

[the width 10mm, the height 6mm, the thickness 4mm]

Capacitance: 1000pF (printed with 102J)

[the width 14mm, the height 9mm, the thickness 4mm]

These capacitors have no polarity.

Variable Capacitors

Variable capacitors are used for adjustment etc. of

frequency mainly.

On the left in the photograph is a "trimmer," which uses ceramic as the dielectric. Next

to it on the right is one that uses polyester film for the dielectric.

The pictured components are meant to be mounted on a printed circuit board.

When adjusting the value of a variable

capacitor, it is advisable to be careful.

One of the component's leads is connected

to the adjustment screw of the capacitor.

This means that the value of the capacitor

can be affected by the capacitance of the

screwdriver in your hand. It is better to use a special screwdriver to adjust these

components.

Pictured in the upper left photograph are variable capacitors with the following

specifications:

Capacitance: 20pF (3pF - 27pF measured)

[Thickness 6 mm, height 4.8 mm]

Their are different colors, as well. Blue: 7pF (2 - 9), white: 10pF (3 - 15), green: 30pF

(5 - 35), brown: 60pF (8 - 72).

In the same photograph, the device on the right has the following specifications:

Capacitance: 30pF (5pF - 40pF measured)

[The width (long) 6.8 mm, width (short) 4.9 mm, and the height 5 mm]

The components in the photograph on the right are used for radio tuners, etc. They are

called "Varicons" but this may be only in Japan.

The variable capacitor on the left in the photograph, uses air as the dielectric. It

combines three independent capacitors.

For each one, the capacitance changed 2pF - 18pF. When the adjustment axis is turned,

the capacitance of all 3 capacitors change simultaneously.

Physically, the device has a depth of 29 mm, and 17 mm width and height. (Not

including the adjustment rod.)

There are various kinds of variable capacitor, chosen in accordance with the purpose for

which they are needed. The pictured components are very small.

To the right in the photograph is a variable capacitor using polyester film as the

dielectric. Two independent capacitors are combined.

The capacitance of one side changes 12pF - 150pF, while the other side changes from

11pF - 70pF.

Physically, it has a depth of 11mm, and 20mm width and height. (Not including the

adjustment rod.)

The pictured device also has a small trimmer built in to each capacitor to allow for

precise adjustment up to 15pF.

Diodes

Example:        Circuit symbol:   

Function

Diodes 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.

Forward Voltage Drop

Electricity uses up a little energy pushing its

way through the diode, rather like a person

pushing through a door with a spring. This means that there is a small voltage across a

conducting diode, it is called the forward voltage drop and is about 0.7V for all normal

diodes which are made from silicon. The forward voltage drop of a diode is almost

constant whatever the current passing through the diode so they have a very steep

characteristic (current-voltage graph).

Reverse Voltage

When a reverse voltage is applied a perfect diode does not conduct, but all real diodes

leak a very tiny current of a few µA or less. This can be ignored in most circuits because

it will be very much smaller than the current flowing in the forward direction. However,

all diodes have a maximum reverse voltage (usually 50V or more) and if this is

exceeded the diode will fail and pass a large current in the reverse direction, this is called

breakdown.

Ordinary diodes can be split into two types: Signal diodes which pass small currents of

100mA or less and Rectifier diodes which can pass large currents. In addition there are

LEDs (which have their own page) and Zener diodes (at the bottom of this page).

Testing diodes

You can use a multimeter or a simple   tester (battery, resistor and LED) to check that a

diode conducts in one direction but not the other. A lamp may be used to test a

rectifier   diode , but do NOT use a lamp to test a

signal   diode because the large current passed by the lamp

will destroy the diode!

.

Rectifier diodes (large current)

Rectifier diodes are used in power supplies to convert

alternating current (AC) to direct current (DC), a process

called rectification. They are also used elsewhere in

circuits where a large current must pass through the diode.

All rectifier diodes are made from silicon and therefore have a forward voltage drop of

0.7V. The table shows maximum current and maximum reverse voltage for some popular

rectifier diodes. The 1N4001 is suitable for most low voltage circuits with a current of

less than 1A.

DiodeMaximum

Current

Maximum

Reverse

Voltage

1N4001 1A 50V

1N4002 1A 100V

1N4007 1A 1000V

1N5401 3A 100V

1N5408 3A 1000V

Bridge rectifiers

There are several ways of connecting

diodes to make a rectifier to convert AC

to DC. The bridge rectifier is one of them

and it is available in special packages

containing the four diodes required.

Bridge rectifiers are rated by their

maximum current and maximum reverse voltage. They have four leads or terminals: the

two DC outputs are labelled + and -, the two AC inputs are labelled.

The diagram shows the operation of a bridge

rectifier as it converts AC to DC. Notice how

alternate pairs of diodes conduct.

Various types of Bridge Rectifiers

Note that some have a hole through their centre for attaching to a heat sink

Zener diodes

Example:      Circuit symbol:  

                  a = anode, k = cathode

Zener diodes are used to maintain a fixed voltage. They

are designed to 'breakdown' in a reliable and non-

destructive way so that they can be used in reverse to

maintain a fixed voltage across their terminals. The

diagram shows how they are connected, with a resistor

in series to limit the current.

Zener diodes can be distinguished from ordinary diodes by their code and breakdown

voltage which are printed on them. Zener diode codes begin BZX... or BZY... Their

breakdown voltage is printed with V in place of a decimal point, so 4V7 means 4.7V for

example.

Zener diodes are rated by their breakdown voltage and maximum power:

The minimum voltage available is 2.7V.

Power ratings of 400mW and 1.3W are common.

Light Emitting Diodes (LEDs)

Example:        Circuit symbol:   

Function

LEDs emit light when an electric current passes through them.

Connecting and soldering

LEDs must be connected the correct way round, the diagram may be

labelled a or + for anode and k or - for cathode (yes, it really is k, not

c, for cathode!). The cathode is the short lead and there may be a

slight flat on the body of round LEDs. If you can see inside the LED the cathode is the

larger electrode (but this is not an official identification method).

LEDs can be damaged by heat when soldering, but the risk is small unless you are very

slow. No special precautions are needed for soldering most

Testing an LED

Never connect an LED directly to a battery or power supply!

It will be destroyed almost instantly because too much current

will pass through and burn it out.

LEDs must have a resistor in series to limit the current to a safe

value, for quick testing purposes a 1k resistor is suitable for

most LEDs if your supply voltage is 12V or less. Remember to connect the LED the

correct way round!

. Tri-colour LEDs

The most popular type of tri-colour LED has a red and a green LED

combined in one package with three leads. They are called tri-colour

because mixed red and green light appears to be yellow and this is produced

when both the red and green LEDs are on.

The diagram shows the construction of a tri-colour LED. Note the different

lengths of the three leads. The centre lead (k) is the common cathode for

both LEDs, the outer leads (a1 and a2) are the anodes to the LEDs allowing

each one to be lit separately, or both together to give the third colour.

Bi-colour LEDs

A bi-colour LED has two LEDs wired in 'inverse parallel' (one forwards, one backwards)

combined in one package with two leads. Only one of the LEDs can be lit at one time and

they are less useful than the tri-colour LEDs described above.

Sizes, Shapes and Viewing angles of LEDs

LEDs are available in a wide variety of sizes and shapes. The

'standard' LED has a round cross-section of 5mm diameter and this is

probably the best type for general use, but 3mm round LEDs are also

popular.

Round cross-section LEDs are frequently used and they are very easy to install on boxes

by drilling a hole of the LED diameter, adding a spot of glue will help to hold the LED if

necessary. LED clips are also available to secure LEDs in holes. Other cross-section

shapes include square, rectangular and triangular.

As well as a variety of colours, sizes and shapes, LEDs also vary in their viewing angle.

This tells you how much the beam of light spreads out. Standard LEDs have a viewing

angle of 60° but others have a narrow beam of 30° or less.

Rapid Electronics stock a wide selection of LEDs and their catalogue is a good guide to

the range available.

Calculating an LED resistor value

An LED must have a resistor connected in series to

limit the current through the LED, otherwise it will

burn out almost instantly.

The resistor value, R is given by:

R = (VS - VL) / I

VS = supply voltage

VL = LED voltage (usually 2V, but 4V for blue and white LEDs)

I = LED current (e.g. 20mA), this must be less than the maximum permitted

If the calculated value is not available choose the nearest standard resistor value which is

greater, so that the current will be a little less than you chose. In fact you may wish to

LED Clip

choose a greater resistor value to reduce the current (to increase battery life for example)

but this will make the LED less bright.

For exampleIf the supply voltage VS = 9V, and you have a red LED (VL = 2V), requiring a current I =

20mA = 0.020A,

R = (9V - 2V) / 0.02A = 350 , so choose 390 (the nearest standard value which is

greater).

Working out the LED resistor formula using Ohm's lawOhm's law says that the resistance of the resistor, R = V/I, where:

  V = voltage across the resistor (= VS - VL in this case)

  I = the current through the resistor

So   R = (VS - VL) / I

Connecting LEDs in series

If you wish to have several LEDs on at the same time it

may be possible to connect them in series. This

prolongs battery life by lighting several LEDs with the

same current as just one LED.

All the LEDs connected in series pass the same

current so it is best if they are all the same type. The

power supply must have sufficient voltage to provide

about 2V for each LED (4V for blue and white) plus at

least another 2V for the resistor. To work out a value for the resistor you must add up all

the LED voltages and use this for VL.

Flashing LEDs

Flashing LEDs look like ordinary LEDs but they contain an integrated circuit (IC) as well

as the LED itself. The IC flashes the LED at a low frequency, typically 3Hz (3 flashes per

second). They are designed to be connected directly to a supply, usually 9 - 12V, and no

series resistor is required. Their flash frequency is fixed so their use is limited and you

may prefer to build your own circuit to flash an ordinary LED, for example our

Flashing   LED project which uses a 555 astable circuit.

LED Displays

LED displays are packages of many LEDs arranged in a pattern, the most familiar pattern

being the 7-segment displays for showing numbers (digits 0-9). The pictures below

illustrate some of the popular designs:

Bargraph 7-segment Starburst Dot matrix

Pin connections of LED displays

There are many types of LED display and a

supplier's catalogue should be consulted for the pin

connections. The diagram on the right shows an

example from the. Like many 7-segment displays,

this example is available in two versions: Common

Anode (SA) with all the LED anodes connected

together and Common Cathode (SC) with all the

cathodes connected together. Letters a-g refer to the

7 segments, A/C is the common anode or cathode as appropriate (on 2 pins). Note that

some pins are not present (NP) but their position is still numbered.

Pin connections diagram

.

Regulator

7805 is an integrated three-terminal positive fixed linear voltage regulator. It supports an

input voltage of 7 volts to 35 volts and output voltage of 5 volts. It typically has a current

rating of 1 amp although both higher and lower current models are available. Its output

voltage is fixed at 5.0V. The 7805 also have a built-in current limiter as a safety feature.

The 7805 will automatically reduce output current if it gets too hot. It belongs to a family

of three-terminal positive fixed regulators with similar specifications and differing fixed

voltages from 8 to 15 volts.

The last two digits represent the voltage; for instance, the 7812 is a 12-volt regulator. The

78xx series of regulators is designed to work in complement with the 79xx series of

negative voltage regulators in systems that provide both positive and negative regulated

voltages, since the 78xx series can't regulate negative voltages in such a system.

The 7805 is one of the most common and well known of the 78xx series regulators, as its

small component count and medium-power regulated 5V make it useful for powering

TTL.

Voltage Regulator (regulator), usually having three legs, converts varying input voltage and produces a constant regulated output voltage. They are available in a variety of outputs.   The most common part numbers start with the numbers 78 or 79 and finish with two digits indicating the output voltage. The number 78 represents positive voltage and 79 negative one. The 78XX series of voltage regulators are designed for positive input. And the 79XX series is designed for negative input.  Examples:            5V DC Regulator Name: LM7805 or MC7805          -5V DC Regulator Name: LM7905 or MC7905          6V DC Regulator Name: LM7806 or MC7806          -9V DC Regulator Name: LM7909 or MC7909 The LM78XX series typically has the ability to drive current up to 1A. For application requirements up to 150mA, 78LXX can be used. As mentioned above, the component has three legs: Input leg which can hold up to 36VDC Common leg (GND) and an output leg with the regulator's voltage. For maximum voltage regulation, adding a capacitor in parallel between the common leg and the output is usually recommended. Typically a 0.1MF capacitor is used. This eliminates any high frequency AC voltage that could otherwise combine with the output voltage. See below circuit diagram which represents a typical use of a voltage regulator.   

 

Lm7805 Heat sink Note:   As a general rule the input voltage should be limited to 2 to 3 volts above the output voltage. The LM78XX series can handle up to 36 volts input, be advised that the power difference between the input and output appears as heat. If the input voltage is unnecessarily high, the regulator will overheat. Unless sufficient heat dissipation is provided through heat sinking, the regulator will shut down.

MICROCONTROLLER

A microcontroller (also microcontroller unit, MCU or µC) is a small computer on a single integrated circuit consisting of a relatively simple CPU combined with support functions such as a crystal oscillator, timers, watchdog, serial and analog I/O etc. Program memory in the form of NOR flash or OTP ROM is also often included on chip, as well as a, typically small, read/write memory.Microcontrollers are designed for small or dedicated applications. Thus, in contrast to the microprocessors used in personal computers and other high-performance or general purpose applications, simplicity is emphasized. Some microcontrollers may operate at clock frequencies as low as 32kHz, as this is adequate for many typical applications, enabling low power consumption (mill watts or microwatts). They will generally have the ability to retain functionality while waiting for an event such as a button press or other interrupt; power consumption while sleeping (CPU clock and most peripherals off) may be just Nan watts, making many of them well suited for long lasting battery applications. Other microcontrollers may serve performance-critical roles, where they may need to act more like a Digital signal processor (DSP), using higher clock speeds and not needing such very low powered operation.

Microcontrollers are used in automatically controlled products and devices, such as automobile engine control systems, remote controls, office machines, appliances, power tools, and toys. By reducing the size and cost compared to a design that uses a separate microprocessor, memory, and input/output devices, microcontrollers make it economical to digitally control even more devices and processes. Mixed signal microcontrollers are

common, integrating analog components needed to control non-digital electronic systems.

SCOPE AND CONCLUSION

This project is used in bio-medical instrumentation. It is used to sense and control the temperature.

References

www.datasheetarchive.com

www.google.com

www.wikipedia.com

www.answers.com