GSM based irrigation system

Abstract— Irrigation is the process of artificiallysupplying water to land where crops are cultivated.Traditionally hand pumps, canal water and rainfall werea major source of water supply for irrigation. Thismethod has led to severe drawbacks like underirrigation, over-irrigation which in turn causesleaching and loss of nutrient content of soil. Changingenvironmental conditions and shortage of water have ledto the need for a system which efficiently managesirrigation of fields. Automated irrigation system is amachine based system, which automates the irrigation ofland by combining various software and hardwareapproaches together for field irrigation.This paper deals with a detailed survey of various GSM

based automated farm irrigation systems. GSM serves asan important part since it is responsible forcontrolling the irrigation facility and sends them toreceiver through coded signal. Our study isconcentrated on comparison of various GSM approaches.

I. INTRODUCTIONIrrigation is a scientific process of artificially

supplying water to the land or soil that is beingcultivated. Traditionally in dry regions having no orlittle rainfall water had to be supplied to the fieldseither through canals or hand pumps, tube wells. Butthis method had severe problems such as increase inworkload of farm labor and often it lead to problemsuch as over-irrigation or under-irrigation, andleaching of soil. Further there were issues likeweeding, lesser yield of crop as an effect of abovementioned problems.Hence there was a need for a way to test the soil

condition before supplying water to the fields. Thismechanism would reduce the workload of the farmer andhelp maintain proper soil conditions for improved andbetter crop production. Hence with the advance oftechnology it was possible to design systems thateliminated the direct involvement of the farmer withrespect to irrigation of their fields.

These systems automated the entire irrigation system bycontrolling the motors that irrigated the fields.A GSM based farm irrigation system has two major

technologies behind it, primary being the “GSM” andsecondary one is the controller or processor. GSM(Global System for Mobile Communication) is a standardset used to describe protocols for digital cellularnetworks. This GSM facility serves as an important partfor controlling the irrigation on field and sending theresults to the farmer using coded signals to a mobiledevice which indirectly controls the entire farmirrigation system. The processor or the controllerworks as a central core for functioning of theautomated process after it has been initiated by theGSM based device and finally presents the output to thedevice.This paper contains five detailed comparative study of

GSM based farm irrigation approaches. Now a day, aBluetooth module is also interfaced with theprocessor/controller for simplifying the mobile devicecomplications. It gives a detailed study of theadvantages and disadvantages of the varioustechnologies proposed by the systems in the papersunder study.The system continuously monitors the soil moisture,

water level of the well, temperature, humidity, dewpoint, weather conditions and provides the detailsabout the field to user though SMS. The systemconsists of a centralized unit having a subscribernumber which forms a link between user and deviceand acts as a primary node for sending and receivingthe data though SMSs by the user. The centralizedunit communicates with the system through SMSs whichwill be received by GS with the help of SIM card;

the GSM sends this data to ARM7, after processing itdisplays it on the LCD. The activation command isgiven to start the motor and indirectly activate thetransistorized relay circuit to constantly monitorthe environmental factors and once the requiredlevel is reached the motor is turned off and themessage is sent to the farmer.B] Real time automation of Indian Agricultural

System [2] deals with ARM7 and GSM combined togetherfor programming and developing the automated system.It is very much similar to the system presented inReal-time automization of Agricultural Environmentfor Social Modernization of Indian AgriculturalSystem [1]. In the system, soil moisture is measuredusing dielectric constant of soil and is informed tothe centralized unit which sends a message to thedevice which waits for a certain amount of defaulttime for user response if no response is received itcontinuously monitors the field and keeps on sendingthe parameters to the centralized unit where it isstored in the EEPROM of ARM. Additionally, tomonitor the plant or leaf’s health, a leaf wetnesssensor has been used allowing us to forecast diseaseand to protect plan canopy. It uses ARM7TDMI, 16kbRAM, flash memory, In-system programming with timersand serial interfaces and modems for creating thereal time applications.C] Innovative GSM Bluetooth Based Remote Controlled

Embedded System for Irrigation [3] proposes a systemwhere GSM/Bluetooth based remote controlled embeddedsystem is used for irrigation. The system sets theirrigation time depending on the environmentalfactors and can automatically irrigate the field[3]. Information, regarding the status of power

supply, is exchanged between the system using SMSson GSM network. In addition to the GSM a Bluetoothfacility has also been interfaced to themicrocontroller for eliminating the SMS charges andthe range limitations. The system checks for thewater flow from the pump if no water supply isavailable system sends information to user viaBluetooth/SMS. The sensor information is sent to thefarmer and the farmer sends data in the form of SMSsin the GSM network to start of stop the irrigationaccording to the received information. The systemconsists of an 8-bit PIC microcontroller havinginbuilt ADCs and interface to various sensor, pump.

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D] Integration of Wireless Technologies forSustainable Agriculture [4] proposes the system thateliminates the use of wired technology and improves theold method of collecting data and allows the farmer tocontrol their sprinklers remotely. It utilizes wirelesssensor networks to collect real time status ofagricultural field and uses mobile phone to control thewatering of the field using sprinkler.The wireless sensor nodes collect information

regarding water level conditions and send the data tothe central sink node which processes the informationand sends it to the user’s mobile phone and heaccordingly controls the watering of the field usingsprinkler controller. The nodes contain a sensor, radiotransceivers, battery and interfacing circuit [4]. Thesystem proposes the use of sprinklers having two majorfeatures, pulsing (water application depth can becontrolled by a series of on-off cycles)[4] and nozzleorifice control (mechanically activated pin to alterthe area which adjusts the sprinkler flow rate)[4],controlled by the sprinkler controller which in turnhas a GSM modem and a microcontroller. It uses a missedcall instruction format wherein each number of missedcalls is associated with a certain number ofinstructions to be performed, which is calculated bythe microcontroller.

E] Design of Ultra Low Cost Cell Phone Based EmbeddedSystem for Irrigation [5] uses AVR ATMega32microcontroller and includes protection against singlephasing, over current, over voltage, dry running andprobable bearing faults; and alerts the user throughmissed calls/buzzers on completion of tasks. RTC DS1307

and DS18S20 are used for time and temperaturemeasurement [5]. The system offers attractive featureslike automated control based on parameters specifiedthough keyboard, SMS, number of missed calls inspecified duration from user mobile though serial cableand based on the commands received and the presentsensor conditions microcontroller system sends signalto the switch on-off the motor though starter usingrelay. Interfacing is done using RS232, AT commands isused. The SMS is a store and forward [5] way oftransmitting messages.

III. ADVANTAGES AND DISADVANTAGES

The system described in [1] uses ARM7, low powerconsuming processor which is very important. GSMtechnology’s ready availability, simplicity, lesssignal deterioration makes it better for sendingcontrol signals and For critical applicationsrequiring real-time monitoring the field conditioncan be transmitted using radio link [1].The drawback of this system was that GSM has a

fixed maximum cell site range of 35km [1] which isimposed by technical limitations. Secondly, thefarmer needs to be familiar with the entire complexAT commands, and finally soil parameters regardingfertilizers and plant diseases are not incorporatedin the system.The system described in [2] also is a low power

consumer with simple and efficient GSM facilities.

It measures all possible soil environmental factorsincluding the health of the plant and detects amountof water or ice on the leaf’s surface also [2]. Thedrawbacks of the system are firstly farmer has tosuffer SMS costs due to the GSM facility, and badrange of the GSM provider may also act as a limitingfactor to the system.The system described in [3] has incorporated

Bluetooth for remote monitoring which reduces theproblem of range with GSM network and saves SMS costfor the farmer. The smoke sensors used to sendemergency information to user incase of fire infield or burning of motor [3]. The design is lowpower, low cost, small size, robust and highlyversatile. It has the same problems as the systemsabove, that range of GSM and Bluetooth is notdependable and user needs to familiarize himselfwith too many complex AT commands.The system described in [4] uses sprinkler

irrigation rather than traditional motors whichincreases the area of water supply. Also, lowinfiltrated soil can be tackled using this systemand since it is a wireless system it has increasedmobility, portability and suitability in adverseconditions. Also it is low cost and user does nothave to memorize complex instructions due to simplemissed call format. But due to this, it also suffersfrom problem of limited instructions, and farmer hasto remember the number of missed calls for eachinstruction and it may not be possible to reach thenumber of missed calls in that time delay.

The system described in [5] provide optimum waterdistribution in fields based on manual settings,

number of missed calls in specified time duration,SMS from cell phones. It ensures protection of motoragainst overloads and overheating and facesimbalances and also provides automated restarting[5]. It uses buzzers, missed calls for alertpurpose. It’s an ultra low cost due to usage ofobsolete cell phone models [5]. It has a dedicatedvoice based call approach for spoken commands tohelp the illiterate farmers [5]. The only drawbackit has is that it uses the same network operator forcontrol system and user cell phones to ensuregreater probability of successful connection; and itrequires extra storage memory for adding othersensors.372

IV. CONCLUSION

There is an urgent need for a system that makes theagricultural process easier and burden free from thefarmer’s side. With the recent advancement oftechnology it has become necessary to increase theannual crop production output of our country India, anentirely agro-centric economy. The ability to conservethe natural resources as well as giving a splendidboost to the production of the crops is one of the mainaims of incorporating such technology into theagricultural domain of the country. To save farmer’seffort, water and time has been the most importantconsideration. Hence systems need to be designed toprovide this ability efficiently using wireless sensornetworking, sprinkler irrigation, GSM, SMS technology,Bluetooth technology and readily available mobile phonedevices is a certain help to the farmers to get betteryield on a large scale and thereby increasing theagricultural wealth and the economic growth of ourcountry.

In this paper we presented a summarized approach ofvarious different types irrigation systems based on GSMapproach. The project is carried out using ARM7TDMIcore with the help of GSM technologies to ensure afaithful irrigation of the farm field. These systemswere all remotely controlled systems which proposed alow cost information exchange via SMS and GSM network.The soil moisture, humidity and various otherenvironmental factors influencing growth of crops areperiodically sensed using high quality accurate sensorand those values are passed on to theprocessor/controller to calculate required amount ofwater and fertilizers and various other inputs during

irrigation and accordingly supplied to the farm. Thefunctionality of GSM increases the efficiency of theautomated irrigation system by giving it a more userfriendly interface using SMS (Short Message Service)coupled with missed called services and incorporationof Bluetooth for further controlling the system fromthe farmer’s side.

The result of the survey conducted has lead to a verypositive approach on the impact of GSM technology infarm irrigation methods and techniques. The approachesstudied had various pros and cons in the time requiredfor operations or complexity or feasibility and userinteractions. With technology advancing everyday newtechniques have been implemented for further minimizingthe irrigation process like using prebuilt mobile phoneor standalone application software for conduction theirrigation process.

MICROCONTROLLER:-

This amplified signal is then given to the controller. A

microcontroller (also microcomputer, MCU or µC) is a small

computer on a single integrated circuit consisting internally of

a relatively simple CPU, clock, timers, I/O ports, and memory.

Program memory in the form of NOR flash or OTP ROM is also often

included on chip, as well as a typically small amount of RAM.

Microcontrollers are designed for small or dedicated

applications.

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

industry-standard 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.

Pin Description

VCC Supply voltage (all packages except 42-PDIP).

GND Ground (all packages except 42-PDIP; for 42-PDIP GND connects

only the logic core and the embedded program memory).

VDD Supply voltage for the 42-PDIP which connects only the logic

core and the embedded program memory.

PWRVDD Supply voltage for the 42-PDIP which connects only the I/O

Pad Drivers. The application board must connect both VDD and

PWRVDD to the board supply voltage.

PWRGND Ground for the 42-PDIP which connects only the I/O Pad

Drivers. PWRGND and GND are weakly connected through the common

silicon substrate, but not through any metal link. The

application board MUST connect both GND and PWRGND to the board

ground.

Port 0 Port 0 is an 8-bit open drain bi-directional I/O port. As

an output port, each pin can sink eight TTL inputs. When 1s are

written to port 0 pins, the pins can be used as high-impedance

inputs.

Port 0 can also be configured to be the multiplexed low-order

address/data bus during

accesses to external program and data memory. In this mode, P0

has internal pull-ups.

Port 0 also receives the code bytes during Flash programming and

outputs the code bytes

during program verification. External pull-ups are required

during program verification.

Port 1 Port 1 is an 8-bit bi-directional I/O port with internal

pull-ups. The Port 1 output buffers can sink/source four TTL

inputs. When 1s are written to Port 1 pins, they are pulled high

by the internal pull-ups and can be used as inputs. As inputs,

Port 1 pins that are externally being pulled low will source

current (IIL) because of the internal pull-ups.

Port 1 also receives the low-order address bytes during Flash

programming and verification.

Port 2 Port 2 is an 8-bit bi-directional I/O port with internal

pull-ups. The Port 2 output buffers can sink/source four TTL

inputs. When 1s are written to Port 2 pins, they are pulled high

by the internal pull-ups and can be used as inputs. As inputs,

Port 2 pins that are externally being pulled low will source

current (IIL) because of the internal pull-ups.

Port 2 emits the high-order address byte during fetches from

external program memory and during accesses to external data

memory that uses 16-bit addresses (MOVX @ DPTR). In this

application, Port 2 uses strong internal pull-ups when emitting

1s. During accesses to external data memory that use 8-bit

addresses (MOVX @ RI), Port 2 emits the contents of the P2

Special

Function Register.

Port 2 also receives the high-order address bits and some control

signals during Flash programming and verification.

Port 3 Port 3 is an 8-bit bi-directional I/O port with internal

pull-ups. The Port 3 output buffers can sink/source four TTL

inputs. When 1s are written to Port 3 pins, they are pulled high

by the internal pull-ups and can be used as inputs. As inputs,

Port 3 pins that are externally being pulled low will source

current (IIL) because of the pull-ups.

Port 3 receives some control signals for Flash programming and

verification.

Port 3 also serves the functions of various special features of

the AT89S51, as shown in the following table.

RST Reset input. A high on this pin for two machine cycles while

the oscillator is running resets the device. This pin drives High

for 98 oscillator periods after the Watchdog times out. The

DISRTO bit in SFR AUXR (address 8EH) can be used to disable this

feature. In the default state of bit DISRTO, the RESET HIGH out

feature is enabled.

ALE/PROG Address Latch Enable (ALE) is an output pulse for

latching the low byte of the address during accesses to external

memory. This pin is also the program pulse input (PROG) during

Flash programming.

In normal operation, ALE is emitted at a constant rate of 1/6 the

oscillator frequency and may be used for external timing or

clocking purposes. Note, however, that one ALE pulse is skipped

during each access to external data memory.

If desired, ALE operation can be disabled by setting bit 0 of SFR

location 8EH. With the bit set, ALE is active only during a MOVX

or MOVC instruction. Otherwise, the pin is weakly pulled high.

Setting the ALE-disable bit has no effect if the microcontroller

is in external execution mode.

PSEN Program Store Enable (PSEN) is the read strobe to external

program memory.

When the AT89S51 is executing code from external program memory,

PSEN is activated twice each machine cycle, except that two PSEN

activations are skipped during each access to external data

memory.

EA/VPP External Access Enable. EA must be strapped to GND in

order to enable the device to fetch code from external program

memory locations starting at 0000H up to FFFFH. Note, however,

that if lock bit 1 is programmed, EA will be internally latched

on reset.

EA should be strapped to VCC for internal program executions.

This pin also receives the 12-volt programming enable voltage

(VPP) during Flash programming.

XTAL1 Input to the inverting oscillator amplifier and input to

the internal clock operating circuit.

XTAL2 Output from the inverting oscillator amplifier

TRANSFORMATION:-

As already discussed the supply which we get is 220V A.C. supply.

In order to decrease the magnitude of the voltage we make use of

step down transformer. This transformer has more windings in the

primary coil than in the secondary coil. So the voltage output at

the secondary is an A.C. supply with magnitude less than 220V as

shown below:

RECTIFICATION:-

As all the electronic circuits work on DC therefore this low

voltage A.C. cannot be directly fed to our circuit. Thus a

process of rectification is required. In this process, A.C.

voltage is converted into D.C. voltage using two semiconductor

rectifying diodes as shown below:

Now as the two diodes D1 and D2 are connected in the opposite

manner. Therefore one of the diode gets forward biased during the

positive half of the a.c input and other gets forward biased

during the negative half of the a.c. input. Thus during the

positive half cycle rectification takes place through diode

D1(diode D2 being reverse biased, cannot rectify) and during the

negative half cycle, the rectification takes place through the

diode D2(diode D1 being reverse biased, cannot rectify). But as

at least one of the diode always remain in the conducting mode

therefore both the halves of the a.c. input gets rectified and

hence the name full wave rectifier.

SMOOTHING/FILTRATION

The output of the rectification process is a varying D.C. As the

D.C. waveform cannot be varying so it means that rectification is

not 100% efficient due to which there is still some component of

the input A.C. present in the D.C. voltage which is responsible

for the variation. So in order to remove this A.C. component we

require filtration or smoothing of the signal. This can be done

using an electrolytic capacitor of 2200uf. As the capacitor

offers infinite impedance to the D.C. signal and Zero impedance

to the A.C. signal therefore, it allows the A.C. component to

pass through and blocks the D.C. component. This means it will

filter out the D.C. component from the input signal. Thus the

output of the process will be a pure D.C. supply as shown below:

Now there is still some variation indicating that output D.C.

voltage is not having constant magnitude. This is due to the

capacitor used for filtration. Its time of charging and

discharging are not equal due to which the filtration is not up

to the mark. For making the output voltage assume a constant

value we need a voltage regulator.

REGULATION:-

Voltage regulator is used for this purpose mainly from the series

of 78- - of the transistor. For getting the constant output of 5

volts we make use of 7805 voltage regulator. This process takes

place as shown below:

This completes all the processes. Now we have a constant D.C.

supply with us which can be fed to any electronic circuit without

any pro problem

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.

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

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

transformers

In general,

transformers are used for two purposes: signal matching and power

supplies.

 Power Transformers

Power 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.

 Inverters

An "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.

 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 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

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 

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

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.

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.

D.C. MOTOR

In any electric motor, operation is based on simple

electromagnetism. A current-carrying conductor generates a

magnetic field; when this is then placed in an external magnetic

field, it will experience a force proportional to the current in

the conductor, and to the strength of the external magnetic

field. As you are well aware of from playing with magnets as a

kid, opposite (North and South) polarities attract, while like

polarities (North and North, South and South) repel. The internal

configuration of a DC motor is designed to harness the magnetic

interaction between a current-carrying conductor and an external

magnetic field to generate rotational motion.

Let's start by looking at a simple 2-pole DC electric motor (here

red represents a magnet or winding with a "North" polarization,

while green represents a magnet or winding with a "South"

polarization).

Every DC motor has six basic parts -- axle, rotor (a.k.a.,

armature), stator, commutator, field magnet(s), and brushes. In

most common DC motors (and all that BEAMers will see), the

external magnetic field is produced by high-strength permanent

magnets1. The stator is the stationary part of the motor -- this

includes the motor casing, as well as two or more permanent

magnet pole pieces. The rotor (together with the axle and

attached commutator) rotate with respect to the stator. The rotor

consists of windings (generally on a core), the windings being

electrically connected to the commutator. The above diagram shows

a common motor layout -- with the rotor inside the stator (field)

magnets.

The geometry of the brushes, commutator

contacts, and rotor windings are such that

when power is applied, the polarities of

the energized winding and the stator

magnet(s) are misaligned, and the rotor

will rotate until it is almost aligned with

the stator's field magnets. As the rotor

reaches alignment, the brushes move to the

next commutator contacts, and energize the

next winding. Given our example two-pole

motor, the rotation reverses the direction

of current through the rotor winding,

leading to a "flip" of the rotor's magnetic

field, driving it to continue rotating.

In real life, though, DC motors will always

have more than two poles (three is a very

common number). In particular, this avoids

"dead spots" in the commutator. You can

imagine how with our example two-pole

motor, if the rotor is exactly at the

middle of its rotation (perfectly aligned

with the field magnets), it will get

"stuck" there. Meanwhile, with a two-pole

motor, there is a moment where the

commutator shorts out the power supply

(i.e., both brushes touch both commutator

contacts simultaneously). This would be bad

for the power supply, waste energy, and

damage motor components as well. Yet

another disadvantage of such a simple motor

is that it would exhibit a high amount of

torque "ripple" (the amount of torque it

could produce is cyclic with the position

of the rotor).

So since most small DC motors are of a three-pole design, let's

tinker with the workings of one via an interactive animation

(JavaScript required):

You'll notice a few things from this -- namely, one pole is fully

energized at a time (but two others are "partially" energized).

As each brush transitions from one commutator contact to the

next, one coil's field will rapidly collapse, as the next coil's

field will rapidly charge up (this occurs within a few

microsecond). We'll see more about the effects of this later, but

in the meantime you can see that this is a direct result of the

coil windings' series wiring:

There's probably no better way to see how an

average DC motor is put together, than by

just opening one up. Unfortunately this is

tedious work, as well as requiring the

destruction of a perfectly good motor.

Luckily for you, I've gone ahead and done

this in your stead. The guts of a

disassembled Mabuchi FF-030-PN motor (the

same model that Solarbotics sells) are

available for you to see here (on 10 lines /

cm graph paper). This is a basic 3-pole DC

motor, with 2 brushes and three commutator

contacts.

The use of an iron core armature (as in the Mabuchi, above) is

quite common, and has a number of advantages2. First off, the

iron core provides a strong, rigid support for the windings -- a

particularly important consideration for high-torque motors. The

core also conducts heat away from the rotor windings, allowing

the motor to be driven harder than might otherwise be the case.

Iron core construction is also relatively inexpensive compared

with other construction types.

But iron core construction also has several disadvantages. The

iron armature has a relatively high inertia which limits motor

acceleration. This construction also results in high winding

inductances which limit brush and commutator life.

In small motors, an alternative design is often used which

features a 'coreless' armature winding. This design depends upon

the coil wire itself for structural integrity. As a result, the

armature is hollow, and the permanent magnet can be mounted

inside the rotor coil. Coreless DC motors have much lower

armature inductance than iron-core motors of comparable size,

extending brush and commutator life.

Diagram courtesy of MicroMo

The coreless design also allows manufacturers to build smaller

motors; meanwhile, due to the lack of iron in their rotors,

coreless motors are somewhat prone to overheating. As a result,

this design is generally used just in small, low-power motors.

BEAMers will most often see coreless DC motors in the form of

pager motors.

Again, disassembling a coreless motor can

be instructive -- in this case, my hapless

victim was a cheap pager vibrator motor.

The guts of this disassembled motor are

available for you to see here (on 10 lines

/ cm graph paper). This is (or more

accurately, was) a 3-pole coreless DC

motor.

I disembowel 'em so you don't have to...

To get the best from DC motors in BEAMbots, we'll need to take a

closer look at DC motor behaviors -- both obvious and not.

It is based on the principle that when a current-carrying

conductor is placed in a magnetic field, it experiences a

mechanical force whose direction is given by Fleming's Left-hand

rule and whose magnitude is given by

Force, F = B I l newton

Where B is the magnetic field in weber/m2.

I is the current in amperes and

l is the length of the coil in meter.

The force, current and the magnetic field are all in different

directions.

If an Electric current flows through two copper wires that are

between the poles of a magnet, an upward force will move one wire

up and a downward force will move the other wire down.

Figure 1: Force in DC

Motor

Figure 2 : Magnetic Field

in DC Motor

Figure 3 : Torque in DC

Motor

Figure 4 : Current Flow in

DC Motor

The loop can be made to spin by fixing a half circle of copper

which is known as commutator, to each end of the loop. Current is

passed into and out of the loop by brushes that press onto the

strips. The brushes do not go round so the wire do not get

twisted. This arrangement also makes sure that the current always

passes down on the right and back on the left so that the

rotation continues. This is how a simple Electric motor is made.

References

www.datasheetarchive.com

www.google.com

www.wikipedia.com

www.answers.com