DC Motors

These are the motors that are commonly found in the toys and the tape recorders. These motors change the direction of rotation by changing the polarity. Most chips can’t pass enough current or voltage to spin a motor. Also, motors tend to be electrically noisy (spikes) and can slam power back into the control lines when the motor direction or speed is changed.

Specialized circuits (motor drivers) have been developed to supply motors with power and to isolate the other ICs from electrical problems. These circuits can be designed such that they can be completely separate boards.
A very popular circuit for driving DC motors (ordinary or gear head) is called an H-bridge. It’s called that because it looks like the capital letter ‘H’ on classic schematics. The great ability of an H-bridge circuit is that the motor can be driven forward or backward at any speed, optionally using a completely independent power source

IC

IC (Integrated Circuit) means that all the components of the circuit are fabricated on same chip. Digital ICs are a collection of resistors, diodes, and transistors fabricated on a single piece of semiconductor, usually silicon called a substrate, which is commonly referred to as ‘wafer’. The chip is enclosed in a protective plastic or ceramic package from which pins extend out connecting the IC to other device. Suffix N or P stands for dual-in-line (plastic package (DIP)) while suffix J or I stands for dual-in-line ceramic package. Also the suffix for W stands for flat ceramic package.

The pins are numbered counter clockwise when viewed from the top of the package with respect to an identity notch or dot at one end of the chip. The manufacturer’s name can usually be guessed from its logo that is printed on the IC. The IC type number also indicates the manufacturer’s code.

The middle portion i.e. the IC type number tells about the IC function and also the family, which the particular IC belongs to. IC’s that belongs to standard TTL series have an identification number that starts with 74; for e.g. 7402, 74LS04, 74S04 etc.

TRANSFORMER

Transformer works on the principle of mutual inductance. We know that if two coils or windings are placed on the core of iron, and if we pass alternating current in one winding, back emf or induced voltage is produced in the second winding. We know that alternating current always changes with the time. So if we apply AC voltage across one winding, a voltage will be induced in the other winding. Transformer works on this same principle. It is made of two windings wound around the same core of iron. The winding to which AC voltage is applied is called primary winding. The other winding is called as secondary winding.

RESISTORS

The flow of charge (or current) through any material, encounters an opposing force similar in many respect to mechanical friction. This opposing force is called resistance of the material. It is measured in ohms.  In some electric circuits resistance is deliberately introduced in the form of the resistor.

COLOUR CODES 

COLOUR	NUMBER	MULTIPLIER	COLOUR	TOLERANCE
Black	0	100	Gold	5%
Brown	1	101	Silver	10%
Red	2	102	No colour	20%
Orange	3	103
Yellow	4	104
Green	5	105
Blue	6	106
Violet	7	107
Grey	8	108
White	9	109
Gold		10-1
Silver		10-2

  CAPACITORS

  A capacitor can store charge, and its capacity to store charge is called capacitance. Capacitors consist of two conducting plates, separated by an insulating material (known as dielectric). The two plates are joined with two leads. The dielectric could be air, mica, paper, ceramic, polyester, polystyrene, etc.  This dielectric gives name to the capacitor. Like paper capacitor, mica capacitor etc.

Electrolytic Capacitor

Electrolytic capacitors have an electrolyte as a dielectric. When such an electrolyte is charged, chemical changes takes place in the electrolyte. If its one plate is charged positively, same plate must be charged positively in future. We call such capacitors as polarized. Normally we see electrolytic capacitor as polarized capacitors and the leads are marked with positive or negative on the can. Non-electrolyte capacitors have dielectric material such as paper, mica or ceramic. Therefore, depending upon the dielectric, these capacitors are classified.

Ceramic Capacitor

Such capacitors have disc or hollow tabular shaped dielectric made of ceramic material such as titanium dioxide and barium titanate. Thin coating of silver compounds is deposited on both sides of dielectric disc, which acts as capacitor plates. Leads are attached to each sides of the dielectric disc and whole unit is encapsulated in a moisture proof coating. Disc type capacitors have very high value up to 0.001uf. Their working voltages range from 3V to 60000V. These capacitors have very low leakage current. Breakdown voltage is very high.

 DIODE

In this discussion the term diode and rectifier will be used interchangeably; however, the term diode usually implies a small signal device with current typically in the milliamp range; and a rectifier, a power device, conducting from 1 to 1000 amps or even higher. Many diodes or rectifiers are identified as 1N4007. A semiconductor diode consists of a PN junction and has two (2) terminals, an anode (+) and a cathode (-). Current flows from anode to cathode within the diode. A diode and schematic representation are shown below.

An ideal diode is like a light switch in your home. When the switch is closed, the circuit is completed; and the light turns on. An ideal diode & a typical diode characteristic would be:

TRANSISTORS

Junction transistors consist of two junctions made from N-type and P-type semiconductor materials and are called bipolar transistors (two polarities). They have three connections emitter, base, and collector.

The forward biased base/emitter junction causes electrons to be attracted from the emitter area towards the base. Arriving in the base area, most of the negative electrons come under the influence of the more positive collector and are attracted by it. This is shown in the left hand drawing, where the base current plus collector current equals the emitter current. Alpha gain is collector current divided by emitter current, and is always less than 1. Beta gain is collector current divided by base current and can be fairly high number. Therefore, causing a small base current to flow makes a much larger collector current to flow. A small base current controls a large collector current. There is 0.6 volts across the base\emitter junction, where it is forward biased (0.3 volts for germanium).

EEPROM 24C02

Pin no 8 is connected to the positive supply +5 volt. Pin no 4 is ground pin. Pin no 1, 2, 3 is 3 address line. Here we use 0 address base, so we connect all the pins of the 24c02 is to zero point.  Pin no 5 is connected to the port P2.3 and pin no 6 is connected to the p2.2 and pin no 7 is connected to the p2.1 of the 89S52 micro controller.

 VOLTAGE REGULATOR

The PCB can use any power supply that creates a DC voltage between 6 and 12 volts. A 5V voltage regulator (7805) is used to ensure that no more than 5V is delivered to the PCB regardless of the voltage present at the J12 connector (provided that voltage is less than 12VDC). The voltage regulator functions by using a diode to clamp the output voltage at 5VDC regardless of the input voltage – excess voltage is converted to heat and dissipated through the body of the regulator. If a DC supply of greater than 12V is used, excessive heat will be generated, and the PCB may be damaged. If a DC supply of less than 5V is used, insufficient voltage will be present at the regulators output.

If a power supply provides a voltage higher than 7 or 8 volts, the regulator must dissipate significant heat. The “fin” on the regulator body (the side that protrudes upward beyond the main body of the part) helps to dissipate excess heat more efficiently.

Applications:

Machine control

Water pump control

Boilers control- it can be used to control boiler ,furnaces and remote high temperature equpments

COMPONENTS USED:

  Integrated Circuit:

IC89S51  : MCU

IC–7805          :     Voltage regulator

TSOP1738

PC817

Transistor:

T1-T5                       :     BC548

T6-T8                       :     BC557

Resistors:

R1-R3              :     1 K

R4-R14            :     10KΩ

R15-R17          :     100KΩ

R18                  :     56KΩ

R19-R20          :     470E

R21                  :     100 E

R22                  :     4KΩ

Diodes:

D1-D10            :    1N4007

Capacitors:

C1-C2            :     27 PF

C3-C4            :     470 µF

C5                  :     10 µF

C6                  :     100µF

Transformer:

9-0-9, 1A.

Crystal

3.579 MHz

Others

LCD

CD Driver

LED