Automatic Washbasin Controller

To derive the power supply for the circuit, the 230V AC

mains is stepped down by transformer Xl to deliver a secondary output of 12V,

500 mA. The. transformer output is rectified by a full-wave rectifier comprising

diodes DI through D4, filtered by capacitor CI and regulated by IC 7805 (IC4).

Capacitor C2 bypasses the ripples present in the regulated supply. LEDll acts as

the power indicator and Rl3 limits the current through LEDI, the BC 557, BC 547

and few discrete component make a 1khz frequency it emits by ir led, and

transmitted to the air, when some obstacle come front of the TX-RX pair, rx

received it and give signal to lm324 ic, it convert this signal to 0/1, it pass the

relay driver transistor, it on = 1 and off = 0, this on off the relay, it on/off the

light of the project.

Basic Electronics

When a beginner to electronics first looks at a circuit board full of

components he/she is often overwhelmed by the diversity of do-dads. In

these next few sections we will help you to identify some of the simple

components and their schematical symbol. Then you should be able to call

them resistors and transistors instead of “Whatchamacallits”.

Electronic component are classed into either being Passive devices

or Active devices.

A Passive Device is one that contributes no power gain (amplification)

to a circuit or system. It has not control action and does not require any

input other than a signal to perform its function. In other words, “A

components with no brains!” Examples are Resistors, Capactitors and

Inductors

Active Devices are components that are capable of controlling voltages

or currents and can create a switching action in the circuit. In other

words, “Devices with smarts!” Examples are Diodes, Transistors and

Integrated circuits. Most active components are semiconductors.

Resistors:

This is the most common component in electronics. It is used mainly to

control current and voltage within the circuit. You can identify a simple

resistor by its simple cigar shape with a wire lead coming out of each end. It

uses a system of color coded bands to identify the value of the component

(measured in Ohms) *A surface mount resistor is in fact mere millimeters in

size but performs the same function as its bigger brother, the simple

esistor. A potentiometer is a variable resistor. It lets you vary the resistance

with a dial or sliding control in order to alter current or voltage on the fly.

This is opposed to the “fixed” simple resistors.

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.

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 

blue, green, 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 values - the resistor colour code

Condensors/Capacitors:

Capacitors, or "caps", vary in size and shape - from a small surface mount model

up to a huge electric motor cap the size of a paint can. It storages electrical

energy in the form of electrostatic charge. The size of a capacitor generally

determines how much charge it can store. A small surface mount or ceramic cap

will only hold a minuscule charge. A cylindrical electrolytic cap will store a much

larger charge. Some of the large electrolytic caps can store enough charge to kill

a person. Another type, called Tantalum Capacitors, store a larger charge in a

The ResistorColour Code

Colour Number

Black 0

Brown 1

Red 2

Orange 3

Yellow 4

Green 5

Blue 6

Violet 7

Grey 8

White 9

smaller package.This is a measure of a capacitor's ability to store charge. A large

capacitance means that more charge can be stored. Capacitance is

measured in farads, symbol F. However 1F is very large, so prefixes are

used to show the smaller values.

Three prefixes (multipliers) are used, µ (micro), n (nano) and p (pico):

µ means 10-6 (millionth), so 1000000µF = 1F n means 10-9 (thousand-millionth), so 1000nF = 1µF p means 10-12 (million-millionth), so 1000pF = 1nF

Capacitor values can be very difficult to find because there are many

types of capacitor with different labelling systems!

There are many types of capacitor but they can be split into two groups, polarised and unpolarised. Each group has its own circuit symbol.

Polarised capacitors (large values, 1µF +)

Examples:        Circuit symbol:   

Electrolytic Capacitors

Electrolytic capacitors are polarised and they must be connected the

correct way round, at least one of their leads will be marked + or -.

They are not damaged by heat when soldering.

There are two designs of electrolytic capacitors; axial where the leads

are attached to each end (220µF in picture) and radial where both leads

are at the same end (10µF in picture). Radial capacitors tend to be a

little smaller and they stand upright on the circuit board.

It is easy to find the value of electrolytic capacitors because they are

clearly printed with their capacitance and voltage rating. The voltage

rating can be quite low (6V for example) and it should always be

checked when selecting an electrolytic capacitor. It the project parts list

does not specify a voltage, choose a capacitor with a rating which is

greater than the project's power supply voltage. 25V is a sensible

minimum for most battery circuits.

Tantalum Bead Capacitors

Tantalum bead capacitors are polarised and have low voltage ratings

like electrolytic capacitors. They are expensive but very small, so they

are used where a large capacitance is needed in a small size.

Modern tantalum bead capacitors are printed with their capacitance and

voltage in full. However older ones use a colour-code system which has

two stripes (for the two digits) and a spot of colour for the number of

zeros to give the value in µF. The standard colour code is used, but for

the spot, grey is used to mean × 0.01 and white means × 0.1 so that

values of less than 10µF can be shown. A third colour stripe near the

leads shows the voltage (yellow 6.3V, black 10V, green 16V, blue 20V,

grey 25V, white 30V, pink 35V).

For example:   blue, grey, black spot   means 68µF 

For example:   blue, grey, white spot   means 6.8µF 

For example:   blue, grey, grey spot   means 0.68µF 

Unpolarised capacitors (small values, up to 1µF)

Examples:        Circuit symbol:

Small value capacitors are unpolarised and may be connected either

way round. They are not damaged by heat when soldering, except for

one unusual type (polystyrene). They have high voltage ratings of at

least 50V, usually 250V or so. It can be difficult to find the values of

these small capacitors because there are many types of them and

several different labelling systems!

Many small value capacitors have their value printed but without a

multiplier, so you need to use experience to work out what the multiplier

should be!

For example 0.1 means 0.1µF = 100nF.

Sometimes the multiplier is used in place of the decimal point: 

For example:   4n7 means 4.7nF.

Capacitor Number Code

A number code is often used on small capacitors where printing is

difficult: the 1st number is the 1st digit,

the 2nd number is the 2nd digit, the 3rd number is the number of zeros to give the capacitance in pF. Ignore any letters - they just indicate tolerance and voltage rating.

For example:   102   means 1000pF = 1nF   (not 102pF!)

For example:   472J means 4700pF = 4.7nF (J means 5% tolerance).

Diodes:

Diodes are basically a one-way valve for electrical current. They let it flow in one

direction (from positive to negative) and not in the other direction. This is used to

perform rectification or conversion of AC current to DC by clipping off the negative

portion of a AC waveform. The diode terminals are cathode and anode and the

arrow inside the diode symbol points towards the cathode, indicating current flow

in that direction when the diode is forward biased and conducting current. Most

diodes are similar in appearance to a resistor and will have a painted line on one

end showing the direction or flow (white side is negative). If the negative side is

on the negative end of the circuit, current will flow. If the negative is on the ositive

side of the circuit no current will flow.

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 LEDs. 

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!

Colours of LEDs

LEDs are available in red, orange, amber, yellow, green, blue and white. Blue and white LEDs are much more expensive than the other colours.

The colour of an LED is determined by the semiconductor material, not by the colouring of the 'package' (the plastic body). LEDs of all colours are available in uncoloured packages which may be diffused (milky) or clear (often described as 'water clear'). The coloured packages are also available as diffused (the standard type) or transparent. 

Switch :

This is a mechanical part which when pressed makes the current to flow through

it. If the switch is released the current stops flowing through it. This helps to

control a circuit.

Transistors:

The transistor performs two basic functions. 1) It acts as a switch turning current

on and off. 2) It acts as a amplifier. This makes an output signal that is a

magnified version of the input signal. Transistors come in several sizes depending

on their application. It can be a big power transistor such as is used inpower applifiers in your stereo, down to a surface mount (SMT) and even down

to .5 microns wide (I.E.: Mucho Small!) such as in a microprocessor or Integrated

Circuit.

NPN Transistor: Bipolar junction perform the function of amplifications where

a small varying voltage or current applied to the base (the lead on the left

side of the symbol) is proportionately replicated by a much larger voltage or

current between the collector and emitter leads. Bipolar junction refers to

sandwich construction of the semiconductor, where a wedge of "P" material is

placed between two wedges of "N" material. In this NPN construction a small

base current controls the larger current flowing from collector to emitter (the lead

with the arrow).

PNP Transistor:

Similar to NPN transistors, PNP's have a wedge of "N" material

between two wedges of "P" material. In this design, a base current regulates the

larger current flowing from emitter to collector, as indicated by the direction of the

arrow on the emitter lead. In CED players, PNP transistors are used less

frequently that the NPN type for amplification functions.

Batteries:

Symbol of batteries shows +ve terminal by a longer line than the –ve terminal.

For low power circuit dry batteries are used.

Speakers:

These convert electrical signals to accoustic viberations. It comprises a permanent

magnet and a moving coil (through which electrical signal is passed). This moving coil is

fixed to the diaphram which vibrates to produce sound

ICs (Integrated Circuits):Integrated Circuits, or ICs, are complex circuits inside one simple package. Silicon

and metals are used to simulate resistors, capacitors, transistors, etc. It is a space

saving miracle. These components come in a wide variety of packages and sizes.

You can tell them by their "monolithic shape" that has a ton of "pins" coming out

of them. Their applications are as varied as their packages. It can be a simple

timer, to a complex logic circuit, or even a microcontroller (microprocessor with a

few added functions) with erasable memory built inside.

SOLDERING INSTRUCTIONS

1.1 Cleaning for soldering:1. Ensure that parts to be soldered and the PCB are clean and free from dirt or grease.

2. Use isopropyl alcohol with the help of non-static Bristol brush for cleaning.

3. Use lint-free muslin cloth for wiping or alternatively use mild soap solution followed by thorough rinsing with water and drying.

1.2 Tips for good Soldering:

1. Use 15 to 25 watt soldering iron for general work involving small joints and for CMOS IC’s, FETS and ASIC’S use temperature controlled soldering station ensuring that the tip temperature is maintained within 330-350 deg. centigrade.

2. For bigger joints use elevated temperature as per job.

3. Before using a new tip, ensure that it is tinned and before applying the tip to the job, wipe it using a wet sponge.

4. Use 60 : 40 (tin : lead) resin core (18-20 SWG) solder.

5. Ensure that while applying the tip to the job, the tip of the soldering iron is held at an angle such that the tip grazes the surface to be heated and ensure that it does not transfer heat to other joints/ components in its vicinity at the same time heating all parts of joint equally.

6. Heat the joint for just the.right amount of time, during which a very short length of solder flows over the joint and then smoothly withdraw the tip.

7. Do not carry molten solder to the joint.

8. Do not heat the electronic parts for more than 2-4 seconds since most of them are sensitive to heat.

9. Apply one to three mm solder which is neither too less nor too much and adequate for a normal joint.

10. Do not move the components until the molten solder, at the joint has cooled._

1.3 Tips for de-soldering:

1. Remove and re-make if a solder joint is bad or dry.

2. Use a de-soldering pump which is first cocked and then the joint is heated in the same way as during soldering, and when the solder melts, push the release button to disengage the pump.

3. Repeat the above operation 2-3 times until the soldered component can be comfortably removed using tweezers or long nose pliers.

4. Deposit additional solder before using the de-soldering pump for sucking it in case of difficulty in sucking the solder if it is too sparse as this will hasten the de-soldering operation.

5. Alternatively, use the wet de-soldering wick using soldering flux which is nothing but a fine copper braid used as a shield in coaxial cables etc. and then press a short length of the wick using the tip of the hot iron against the joint to be disordered so that the iron melts the solder which is drawn into the braid.

6. Do not allow the solder to cool while the braid is still adhering to the joint.

7. Solder the component again after cleaning by repeating the steps under subpar A and B above.

8. Allow it to cool and check for continuity.

1.4 Precautions:

1. Mount the components at the appropriate places before soldering. Follow the circuit description and components details, leads identification etc. Do not start soldering before making it confirm that all the components are mounted at the right place.

2. Do not use a spread solder on the board, it may cause short circuit.

3. Do not sit under the fan while soldering

4. Position the board so that gravity tends to keep the solder where you want it.

5. Do not over heat the components at the board. Excess heat may damage the components or board.

6. The board should not vibrate while soldering otherwise you have a dry or a cold joint.

7. Do not put the kit under or over voltage source. Be sure about the voltage either dc or ac while operating the gadget.

8. Do spare the bare ends of the components leads otherwise it may short circuit with the other components. To prevent this use sleeves at the component leads or use sleeved wire for connections.

9. Do not use old dark color solder? It may give dry joint. Be sure that all the joints are clean and well shiny.

1.5 Illustrations showing correct/wrong insertion of components and their soldering:

Corrected assembling and soldering process can provide the product in the best performance.

HOW TO MAKE GOODHOMEMADE PCBs?

Do not use sodium hydroxide for developing photoresist laminates. It is completely a

dreadful stuff for developing PCBs. Apart from its causticity, it is very sensitive to

both temperature and concentration, and made-up solution doesn’t last long