WIRE LESS CONTROLLED LAND MINE DETECTION ROBO-VEHICLE

RECEIVER PART

POWER SUPPLY

LAND MINE DETECTOR

BUZZER

MOTOR DRIVER

ROBO-VEHICLE

RF RECEIVER

ANTENNA

TRANSMITTER

(Block diagram)

POWER SUPPLY

SWITCHES

RF TRANSMITTER

ANTENNA

currently, very little technology is used in real-world demining activities. active programs by the u.s. army in both land mine detection sensor

development and systems integration are evaluating new technologies, incrementally improving existing technologies, increasing the probability

of detection, reducing the false alarm rate, and planning out usable deployment scenarios. through iterative design/build test cycles, and blind

and scored testing at army mine lanes, steady progress is being made.

Hardware Used

Power supply section

Pinout of the 7805 regulator IC. Pinout of the 7812 regulator IC.

1. Unregulated voltage in 1. Unregulated voltage in

2. Ground 2. Ground

3. Regulated voltage out 3. Regulated voltage out

The power supply designed for catering a fixed demand connected in

this project. The basic requirement for designing a power supply is as

follows,

1. The voltage levels required for operating the devices is +5volt. Here

+5 Volts required for operating microcontroller. And as well as

required for drivers and amplifiers and IR transmitters and receivers.

2. The current requirement of each device or load must be added to

estimate the final capacity of the power supply.

The power supply always specified with one or multiple voltage outputs

along with a current capacity. As it is estimate the requirement of power

is approximately as follows,

Out Put Voltage = +5Volt, Capacity = 1000mA

The power supply is basically consisting of three sections as follows,

1. Step down section

2. Rectifier Section

3. Regulator section

Design principle:

There are two methods for designing power supply, the average value

method and peak value method. In case of small power supply peak

value method is quit economical, for a particular value of DC output the

input AC requirement is appreciably less. In this method the DC output

is approximately equal to Vm. A full wave bridge rectifier is designed

using two diodes and the output of the rectifier is filtered with a low pass

filter. The capacitor value is decided so that it will back up for the

voltage and current during the discharging period of the DC output. In

this case the output with reference to the center tap of the transformer is

taken in to consideration, though the rectifier designed is a full wave

bridge rectifier but the voltage across the load is a half wave rectified

output. The Regulator section used here is configured with a series

regulator LM78XX the XX represents the output voltage and 78 series

indicates the positive voltage regulator 79 series indicates the negative

regulator for power supply. The positive regulator works satisfactorily

between the voltage XX+2 to 40 Volts DC. The output remains constant

within this range of voltage. The output remains constant within this

range of voltage.

Circuit connection: - In this we are using Transformer (12-0-12) v /

1mA, IC 7805, diodes IN 4007, LED & resistors. Here 230V, 50 Hz ac

signal is given as input to the primary of the transformer and the

secondary of the transformer is given to the bridge rectification diode.

The positive output of the bridge rectifier is given as i/p to the IC

regulator (7805) through capacitor (1000uf/25v). The o/p of the IC

regulator is given to the LED through resistors to act as indicator.

Circuit Explanations: - When ac signal is given to the primary of the

transformer, due to the magnetic effect of the coil magnetic flux is

induced in the coil (primary) and transfer to the secondary coil of the

transformer due to the transformer action.” Transformer is an

electromechanical static device which transformer electrical energy from

one coil to another without changing its frequency”. Here the diodes are

connected to the two +12volt output of the transformer. The secondary

coil of the transformer is given to the diode circuit for rectification

purposes.

During the +ve cycle of the ac signal the diodes D1 conduct due to the

forward bias of the diodes and diodes D2 does not conduct due to the

reversed bias of the diodes. Similarly during the –ve cycle of the ac

signal the diodes D2 conduct due to the forward bias of the diodes and

the diodes D1 does not conduct due to reversed bias of the diodes. The

output of the bridge rectifier is not a power dc along with rippled ac is

also present. To overcome this effect, a low pass filter is connected to

the o/p of the diodes (D1 & D2). Which removes the unwanted ac signal

and thus a pure dc is obtained. Here we need a fixed voltage, that’s for

we are using IC regulators (7805).”Voltage regulation is a circuit that

supplies a constant voltage regardless of changes in load current.” This

IC’s are designed as fixed voltage regulators and with adequate heat

sinking can deliver output current in excess of 1A. The o/p the full wave

rectifier is given as input to the IC regulator through low pass filter with

respect to GND and thus a fixed o/p is obtained. The o/p of the IC

regulator (7805) is given to the LED for indication purpose through

resistor. Due to the forward bias of the LED, the LED glows ON state,

and the o/p are obtained from the pin no-3.

50Hz

IC7805

GND

12-0-12

+5VDC

LED

330R

230VAC

31

2

- +

IN4007

POWER SUPPLY SECTION

ATMEGA32 MICROCONTROLLER

Features

High-performance, Low-power AVR 8-bit Microcontroller Advanced RISC Architecture

– 131 Powerful Instructions – Most Single-clock Cycle Execution– 32 x 8 General Purpose Working Registers– Fully Static Operation– Up to 16 MIPS Throughput at 16 MHz– On-chip 2-cycle Multiplier

High Endurance Non-volatile Memory segments– 32K Bytes of In-System Self-programmable Flash program memory

8-bit– 1024 Bytes EEPROM– 2K Byte Internal SRAM

Microcontroller– Write/Erase Cycles: 10,000 Flash/100,000 EEPROM– Data rete ntion: 20 years at 85°C/100 years at 25°C

(1 ) with 32K Bytes

– Optional Boot Code Section with Independent Lock Bits In-System Programming by On-chip Boot Program In-System True Read-While-Write Operation

– Programming Lock for Software Security

Programmable JTAG (IEEE std. 1149.1 Compliant) Interface

– Boundary-scan Capabilities According to the JTAG Standard– Extensive On-chip Debug Support

Flash– Programming of Flash, EEPROM, Fuses, and Lock Bits through the

JTAG Interface

Peripheral Features– Two 8-bit Timer/Counters with Separate Prescalers and Compare

Modes– One 16-bit Timer/Counter with Separate Prescaler, Compare Mode,

and Capture Mode

– Real Time Counter with Separate Oscillator –Four PWM Channels

– 8-channel, 10-bit ADC Summary

• 8 Single-ended Channels• 7 Differential Channels in TQFP Package Only• 2 Differential Channels with Programmable Gain at 1x, 10x, or

200x– Byte-oriented Two-wire Serial Interface– Programmable Serial USART– Master/Slave SPI Serial Interface– Programmable Watchdog Timer with Separate On-chip Oscillator– On-chip Analog Comparator

Special Microcontroller Features– Power-on Reset and Programmable Brown-out Detection– Internal Calibrated RC Oscillator– External and Internal Interrupt Sources– Six Sleep Modes: Idle, ADC Noise Reduction, Power-save, Power-

down, Standby and Extended Standby I/O and Packages

– 32 Programmable I/O Lines– 40-pin PDIP, 44-lead TQFP, and 44-pad QFN/MLF

Operating Voltages– 2.7 - 5.5V for ATmega32A

Speed Grades– 0 - 16 MHz for ATmega32A

Power Consumption at 1 MHz, 3V, 25 C for ATmega32A– Active: 0.6 mA– Idle Mode: 0.2 mA– Power-down Mode: < 1 µA

Overview

The ATmega32A is a low-power CMOS 8-bit microcontroller based on the AVR enhanced RISC Architecture. By executing powerful instructions in a single clock cycle, the ATmega32A .Achieves throughputs approaching 1 MIPS per MHz allowing the system designed to optimize power consumption versus processing speed.

Pin Configurations

PIN DESCRIPTION

VCC Digital supply voltage.

GNDGround.

Port A (PA7..PA0)

Port A serves as the analog inputs to the A/D Converter.

Port A also serves as an 8-bit bi-directional I/O port, if the A/D Converter is not

used. Port pins can provide internal pull-up resistors (selected for each bit). The

Port A output buffers have symmetrical drive characteristics with both high sink

and source capability. When pins PA0 to PA7 are used as inputs and are

externally pulled low, they will source current if the internal pull-up resistors

are activated. The Port A pins are tri-stated when a reset condition becomes

active, even if the clock is not running.

Port B (PB7..PB0)

Port B is an 8-bit bi-directional I/O port with internal pull-up resistors (selected

for each bit). The Port B output buffers have symmetrical drive characteristics

with both high sink and source capability. As inputs, Port B pins that are

externally pulled low will source current if the pull-up resistors are activated.

The Port B pins are tri-stated when a reset

condition becomes active, even if the clock is not running.Port B also serves the

functions of various special features of the ATmega32

Port C (PC7..PC0)

Port C is an 8-bit bi-directional I/O port with internal pull-up resistors (selected

for each bit). The Port C output buffers have symmetrical drive characteristics

with both high sink and source capability. As inputs, Port C pins that are

externally pulled low will source current if the pull-up resistors are activated.

The Port C pins are tri-stated when a reset

condition becomes active, even if the clock is not running. If the JTAG interface

is enabled, the pull-up resistors on pins PC5(TDI), PC3(TMS) and PC2(TCK)

will be activated even if a reset occurs.

Port C also serves the functions of the JTAG interface and other special features

of the ATmega32.

Port D (PD7..PD0)

Port D is an 8-bit bi-directional I/O port with internal pull-up resistors (selected

for each bit). The Port D output buffers have symmetrical drive characteristics

with both high sink and source capability. As inputs, Port D pins that are

externally pulled low will source current if the pull-up resistors are activated.

The Port D pins are tri-stated when a reset condition becomes active, even if the

clock is not running. Port D also serves the functions of various special features

of the ATmega32.

RESET

Reset Input. A low level on this pin for longer than the minimum pulse length

will generate a reset, even if the clock is not running. The minimum pulse

length is 0.1 vcc. Shorter pulses are not guaranteed to generate a reset.

XTAL1

Input to the inverting Oscillator amplifier and input to the internal clock

operating circuit.

XTAL2

Output from the inverting Oscillator amplifier.

AVCC

AVCC is the supply voltage pin for Port A and the A/D Converter. It should be

externally

Connected to VCC, even if the ADC is not used. If the ADC is used, it should

be connected

to VCC through a low-pass filter.

AREF

AREF is the analog reference pin for the A/D Converter.

ADC• 10-bit Resolution

• 0.5 LSB Integral Non-linearity

• ±2 LSB Absolute Accuracy

• 13 - 260 μs Conversion Time

• Up to 15 kSPS at Maximum Resolution

• 8 Multiplexed Single Ended Input Channels

• 7 Differential Input Channels

• 2 Differential Input Channels with Optional Gain of 10x and 200x(1)

• Optional Left adjustment for ADC Result Readout

• 0 - VCC ADC Input Voltage Range

• Selectable 2.56V ADC Reference Voltage

• Free Running or Single Conversion Mode

• ADC Start Conversion by Auto Triggering on Interrupt Sources

• Interrupt on ADC Conversion Complete

• Sleep Mode Noise Canceler

Note: 1. The differential input channels are not tested for devices in PDIP

Package. This feature is only guaranteed to work for devices in TQFP and

QFN/MLF Packages .The ATmega16 features a 10-bit successive

approximation ADC. The ADC is connected to an 8-channel Analog

Multiplexer which allows 8 single-ended voltage inputs constructed from the

pins of Port A. The single-ended voltage inputs refer to 0V (GND). The device

also supports 16 differential voltage input combinations. Two of the differential

inputs (ADC1, ADC0 and ADC3, ADC2) are equipped with a programmable

gain stage, providing amplification steps of 0 dB (1x), 20 dB (10x), or 46 dB

(200x) on the differential input voltage before the A/D conversion. Seven

differential analog input channels share a common negative terminal (ADC1),

while any other ADC input can be selected as the positive input terminal. If 1x

or 10x gain is used, 8-bit resolution can be expected. If 200x gain is used, 7-bit

resolution can be expected.

The ADC contains a Sample and Hold circuit which ensures that the input

voltage to the ADC is held at a constant level during conversion..

The ADC has a separate analog supply voltage pin, AVCC. AVCC must not

differ morethan ±0.3 V from VCC. See the paragraph “ADC Noise Canceler”

on page 213 on how toconnect this pin.

Internal reference voltages of nominally 2.56V or AVCC are provided On-chip.

The voltage reference may be externally decoupled at the AREF pin by a

capacitor for better noise performance.

Operation

The ADC converts an analogue input voltage to a 10-bit digital value through

successive approximation. The minimum value represents GND and the

maximum value represents the voltage on the AREF pin minus 1 LSB.

Optionally, AVCC or an internal 2.56V reference voltage may be connected to

the AREF pin by writing to the REFSn bits in the ADMUX Register. The

internal voltage reference may thus be decoupled by an external capacitor at the

AREF pin to improve noise immunity.

The analogue input channel and differential gain are selected by writing to the

MUX bits in ADMUX. Any of the ADC input pins, as well as GND and a fixed

band gap voltage reference, can be selected as single ended inputs to the ADC.

A selection of ADC input pins can be selected as positive and negative inputs to

the differential gain amplifier. If differential channels are selected, the

differential gain stage amplifies the voltage difference

between the selected input channel pair by the selected gain factor. This

amplified value then becomes the analogue input to the ADC. If single ended

channels are used, the gain amplifier is bypassed altogether.

The ADC is enabled by setting the ADC Enable bit, ADEN in ADCSRA.

Voltage reference and input channel selections will not go into effect until

ADEN is set. The ADC does not consume power when ADEN is cleared, so it

is recommended to switch off the ADC before entering power saving sleep

modes.

The ADC generates a 10-bit result which is presented in the ADC Data

Registers, ADCH and ADCL. By default, the result is presented right adjusted,

but can optionally be presented left adjusted by setting the ADLAR bit in

ADMUX.

If the result is left adjusted and no more than 8-bit precision is required, it is

sufficient to read ADCH. Otherwise, ADCL must be read first, then ADCH, to

ensure that the content of the Data Registers belongs to the same conversion.

Once ADCL is read, ADC access to Data Registers is blocked. This means that

if ADCL has been read, and a conversion completes before ADCH is read,

neither register is updated and the result from the conversion is lost. When

ADCH is read, ADC access to the ADCH and ADCL Registers is re-enabled.

The ADC has its own interrupt which can be triggered when a conversion

completes. When ADC access to the Data Registers is prohibited between

reading of ADCH and ADCL, the interrupt will trigger even if the result is lost.

Starting a Conversion

A single conversion is started by writing a logical one to the ADC Start

Conversion bit,ADSC. This bit stays high as long as the conversion is in

progress and will be cleared by hardware when the conversion is completed. If a

different data channel is selected while a conversion is in progress, the ADC

will finish the current conversion before performing the channel change.

Alternatively, a conversion can be triggered automatically by various sources.

Auto Triggering is enabled by setting the ADC Auto Trigger Enable bit,

ADATE in ADCSRA. The trigger source is selected by setting the ADC Trigger

Select bits, ADTS in SFIOR When a positive edge occurs on the selected

trigger signal, the ADC prescaler is reset and a conversion is started. This

provides a method of starting conversions at fixed intervals. If the trigger signal

still is set when the conversion completes, a new conversion will not be started.

If another positive edge occurs on the trigger signal during conversion, the edge

will be ignored. Note that an Interrupt Flag will be set even if the specific

interrupt is disabled or

the global interrupt enable bit in SREG is cleared. A conversion can thus be

triggered without causing an interrupt. However, the Interrupt Flag must be

cleared in order to trigger a new conversion at the next interrupt event

Motor drivers

L293D

L293D has two channels. i.e, you can connect two motors to the same bridge. I

have driven 4 motors of 250mA using L293D, with 2 motor in each channel. Now

let's see the ratings of L293D Output Current 1 A Per Channel (600 mA for

L293D) Peak Output Current 2 A Per Channel (1.2 A for L293D) Maximum VC –

4.5 to 36V (>VSS)( it should be greater than or equal the supply voltage,vss) input

side(input to L293D from parallel port or microcontroller) VIH High-level input

voltage( a voltage which L293D takes input as HIGH(1))

VC ≤7 V (2.3 to VC)

VC ≥7 V (2.3 to 7 V)

VIL High-level input voltage( a voltage which L293D takes input as LOW(0))

(-.3 to 1.5V), remember that VIL should not be less than -.3V output side(output of

L293D to motor) VOH High-level output voltage (VCC2 − 1.8, VCC2 − 1.4) VOL

Low-level output voltage (1.2v , 1.8v)

If you want to use PWM to control L293D then apply PWM output to the chip

inhibit of the IC. Remember all these parameters when you connect L293D in

circuits. L293B are available, if you use it use 4 external protection diodes. L293D

costs around Rs.90. I have seen too many post about the problems occurring

L293D, so here i am explaining things in more detail, how to connect L293D in

circuit so that it won't create any problems to you.

TROUBLESHOOTING L293D:

1. Insert IC into the breadboard. Make sure that IC is inserted properly into

breadboard. You can verify it using continuity test in the multi-meter. Test

continuity between the pins of the IC and the holes of the breadboard. If you get a

beep then you can sure that IC is fitted strongly into breadboard and the portion of

breadboard you are using is good.

2. Test the continuity in the 16 pins of the IC and the breadboard holes, to make

sure that nothing goes wrong. You should be thorough with the steps you are

taking.

3. Apply Vss=5V (Pin 16) . The first thing to apply when you connect an IC is

applying Vcc and ground. Remember Vss should be in the range of 4.5V to 7V

4. Now connect ground at Pins 4, 5, 12, 13. Remember if you use multiple

supplies, you should short circuit all grounds and this ground is applied to the Pins.

5. Now Vss and Gnd applying is over.

6. Now apply +5V to chip enable pins. Chip enable pins are pin1,9

7. Here we are trying to use both channels, at least test both channels of the IC so

that we can test whether IC is good or not.

8. Apply Vc at Pin8. For testing the IC you can apply Vc=Vss=5V. When you

connect the motor you should apply Vc>Vss or may it can be equal also. I have

tested it.

9. The following test are done for each channels separately. In the following

explanation I refer '1' as +5V (Vss) and '0' as ground.

10. Apply Input 1 = Input 2 =0(reground) and connect multimeter to output 1 and

ground of the circuit. Now test output1 and output2 voltages. Both should be zero

at this condition.

11. Apply Input1=1 and Input2=0 and check voltages at output1 and output2.

Remember your multimeter's one lead should be ground. Then you should get one

output= Vc and other output = 0. Suppose

if you got output1=Vc and output2=0.

12. Apply Input1=0 and Input2=1 and check voltages at output1 and output2. Then

output1=0 and output2=Vc. That is this case is should be reverse of the previous

case, motor will rotate in opposite

direction.

13. Apply Input1=1 and Input2=1 and check voltages at output1 and output2. Then

output1=output2=Vc. This is the braking case.

14. Test conditions 10-13 for both channels to test the IC is good. You should test

it thoroughly so that a repetition is not needed. If your IC is not working, repeat

steps 1-13 to make sure IC is bad.

15. the most problems occurring are breadboard problems, IC not inserted

properly, applying Vss and Vc wrongly (this can sometimes cause problems to IC),

not disabling chip inhibit, absence of common ground.

16. If you are applying Vc=Vss = +5V, then you can use two LED's to see outputs.

17. When chip inhibit is enabled, ie chip is not working the outputs will be high

impedance, you can test high impedance using an LED. First connect the cathode

of LED to ground through a series resistor of

330ohm and test the output. LED will not glow. The apply 5V to the anode of the

LED and apply output to the cathode through a series resistor of 330 ohm. Now

also LED won't glow. Now you can assure that the output is high impedance.

18. Before connecting motor to the outputs of L293D, first test the motor is

working with the desired VC by applying VC and ground directly to the two leads

of the motor. Confirm this first, then connect the motor.

19. L293d has a thermal shutdown function. So see it is working in all conditions

of the circuit and robot

Metal Detecting Sensor

Detects metal objects upto 7 cm giving active low

output with LED indication & buzzer on detectingmetal.

Applications

Detect presence of any metallic objectLocate pipes, cables, metal studs, …Avoid disasters when drilling holes in wallsGreat project for novicesYour own unique applicationInterface with any microcontroller

Specifications

Detection range adjustable up to 7 cmOperation range varies according to size of the metallic objectPower Supply : 5V DC Power Consumption: 50mA max.Detection Indicator LED and BuzzerDigital output. Active with logic “0”Dimensions : 52x71 mmFull SMD design

Using the Sensor

Connect regulated DC power supply of 5 Volts. Blackwire is Ground, Next middle wire is Brown which is outputand Red wire is positive supply. These wires are alsomarked on PCB.When adjusting sensitivity move away from any metalobject.Turn sensitivity pre-set until the LED is about to light. Toset maximum sensitivity, turn preset until the LED isweakly lit and just becomes off.To test sensor you only need power the sensor by

connect two wires +5V and GND. You can leave theoutput wire as it is. When LED is off the output is at 5V.Bring the metal object nearby the PCB coil and the LEDwill lit up and output becomes 0V.The output is active low and can be given directly to microcontroller for interfacingapplications.

Operation

The heart of this sensor is the inductive oscillator circuit which monitors high frequency current lossin coil. The circuit is designed for any metallic body detection by detecting the variations in the highfrequency Eddy current losses. With an external tuned circuit they act as oscillators. Output signallevel is altered by an approaching metallic object.Output signal is determined by supply current changes. Independent of supply voltage, thiscurrent is high or low according to the presence or the absence of a close metallic object. If themetal object is near the searching coil, the output current will flow more. On the other hand, the

current will be decrease when the object is far from the searching coil.

3V PCB Mount Piezo Buzzer

Compact PCB Mount Buzzers in AC and DC type, ideal for use with Microcontrollers and Control Systems. Low current consumption and loud sound output.

Features

Resonant Frequency: 4,500Hz Rated Voltage: 3Vdc (DC input) Operating Voltage: 3 - 18Vdc Rated Current: 5mA @ 5Vdc Sound Pressure Level: 70dB @ 3Vdc Weight: 1 gram Dimensions: 12mm Diameter, 8.5mm High, Pin Spacing - 7.5mm

RF TRANSMITTER

Introduction

Radio Frequency Technology

Radio Frequency (RF) in the range of 3 Hz and 30 GHz. RF communications are typically

support 1200 to 9600 baud. Recently developed modulation schemes and spread spectrum

technologies are achieving up to 19,200 baud.

RF technology evolution challenges:

Higher frequency utilization

Higher bit rates and thus larger BW’s

RF is affected by absorption, multi path interference, EMI etc.

RF is affected by material like steel, wall, window glass etc.

Radio based on frequency convertible platforms. Flexible and scalable modular architecture.

Increased integration to fit new standards and frequencies in the same cabinet Co-sitting

capabilities with other standards requires high performance transmitters and receivers.

RF Network Configuration:

System Identification

Should be unique

Channel / Frequency

Should have minimal interference with other systems

Data Rates.

TLP434A Ultra Small Transmitter Diagram

Frequency 315, 418 and 433.92 Mhz

Modulation : ASK

Operation Voltage : 2 - 12 VDC

Pin Specifications

Pin 1: GND

Pin 2: Data In

Pin 3: Vcc

Pin 4: Antenna (RF output)

RF Transmitter Specifications

Application Circuit

Typical Key-chain Transmitter using HT12E-18DIP, a Binary 12 bit Encoder from Holtek

Semiconductor Inc.

RECEIVER

Introduction

Radio Frequency Technology:

Radio Frequency (RF) in the range of 3 Hz and 30 GHz. RF communications are typically

support 1200 to 9600 baud. Recently developed modulation schemes and spread spectrum

technologies are achieving up to 19,200 baud.

RF technology evolution challenges:

Higher frequency utilization

Higher bit rates and thus larger BW’s

RF is affected by absorption, multi path interference, EMI etc.

RF is affected by material like steel, wall, window glass etc.

Radio based on frequency convertible platforms. Flexible and scalable modular architecture.

Increased integration to fit new standards and frequencies in the same cabinet. Co-sitting

capabilities with other standards requires high performance transmitters and receivers.

RF Network Configuration:

System Identification

Should be unique

Channel / Frequency

Should have minimal interference with other systems

Data Rates

RLP434A SAW Based Receiver Diagram

Frequency 315, 418 and 433.92 MHz

Modulation : ASK

Supply Voltage : 3.3 - 6.0 VDC

Output : Digital & Linear

Pin Specifications

Pin 1: Gnd

Pin 2: Digital Data Output

Pin 3: Linear Output /Test

Pin 4: Vcc

Pin 5: Vcc

Pin 6: Gnd

Pin 7: Gnd

Pin 8: Antenna

RF Receiver Specifications

Application Circuit

Typical RF Receiver using HT12D-18DIP, a Binary 12 bit Decoder with 8 bit uC HT48RXX

from Holtek Semiconductor Inc.

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,

commentator, field magnet(s), and brushes. In most common DC motors, 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) rotates 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).