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SENSORS - CURRENT SENSORAutomatic Street Light

Automatic Street light

An introduction:

Needs no manual operation for switching ON and OFF. When there is need of light. It detects itself weather there is need for light or not. When darkness rises to a certain value then automatically street light is switched ON and when there is other source of light i.e. day time, the street light gets OFF. The sensitiveness of the street light can also be adjusted. In our project we have used four L.E.D for indication of bulb but for high power switching one can connect Relay (electromagnetic switch) at the output of pin 3 of I.C 555. Then it will be possible to turn ON/OFF any electrical appliances connected all the way through relay.

Principle :

This circuit uses a popular timer I.C 555. I.C 555 is connected as comparator with pin-6 connected with positive rail, the output goes high(1) when the trigger pin 2 is at lower then 1/3rd level of the supply voltage. Conversely the output goes low (0) when it is above 1/3rd level. So small change in the voltage of pin-2 is enough to change the level of output (pin-3) from 1 to 0 and 0 to 1. The output has only two Burglar Alarm

The circuit illustrated here is used as an Burglar alarm. LDR is kept at such a place that when thief enters our house then a shadow will fall on the LDR. A small beam of light source is also needed to supply continuous signal to LDR. For best Light source we can use Laser diode which will work for few KMs. For home use Infra Red LED’s will be good and will be tricky to thief and works with same efficiency at night.

This circuit uses a popular timer I.C which is 555. I.C 555 is connected as comparator with pin 6 connected with positive supply, the output goes high-1 when the trigger pin 2 is at lower than 1/3 level of the supply voltage. Conversely the output goes low-0 when it is above 1/3. So small change in voltage of pin 2 is enough to change the output state of pin 3 from 1 to 0 and 0 to 1. The output has only two states high and low and can not remain in any intermediate stage. Burglar Alarm Circuit Diagram

LED = Light Emitting Diode

LDR = Light Dependent Resistance

IC = Integrated Circuit

Components:-

1) 9V battery with snap

2)LDR

3)Variable resistance 100K ohms

4)Resistance 470 ohms

5)LED

6)IC 555

7)Switch

It is power by 9V battery for portable use. The circuit is economic in power consumption. Pin 4,6& 8 is connected to the positive supply and pin 1 is grounded.

To detect the present robber we have used LDR and a source of light.

LDR is a special type of resistance whose value depends on the brightness of the light which is falling on it. It has a resistance of about 1 megaohms when in total darkness,but a resistance of only about 2-5 k ohms when brightly illuminated. It responds to a large part of the light spectrum.

The source of light and LDR is so adjusted with a reflector that light will directly fall on the LDR but when robber enters inside then it will block the beam of light and LDR will be under darkness.

We have made a potential divider circuit with LDR and 100 K variable resistance connected in series. Voltage is directly proportional to conductance so more voltage we will get by this divider when LDR is getting light and low voltage in darkness. Sensitiveness can be adjusted by variable resistance. Divided voltage is given to pin 2nd of 555. As soon as LDR gets dark the voltage of the pin 2 drops 1/3 of the supply voltage and pin 3 gets high and Buzzer Beeps.

For Demo we have used simple LED for LED1 may be Red or White Color

states high and low and can not remain in any intermediate stage. It is powered by a 6V battery for portable use. The circuit is economic in power consumption. Pin 4, 6 and 8 is connected to the positive supply and pin 1 is grounded. To detect the present of an object we have used LDR and a source of light. LDR is a special type of resistance whose value depends on the brightness of the light which is falling on it. It has resistance of about 1 mega ohm when in total darkness, but a resistance of only about 5k ohms when brightness illuminated. It responds to a large part of light spectrum. We have made a Electronic Eye

ELECTRONIC EYE PROJECT

THEORY AND CIRCUIT DIAGRAM

Electronic eye has much use in this electronic age. Also Known as magic eye. It can be used as an automatic guest indicator at the door, If fitted on the bottom of the door entrance. Once it is installed at the door there is no need to install a call bell. It can also be used at homes or in banks as a burglar alarm.

Fix the LDR to the wooden door or a locker to be protected in such a manner that when anybody tries to open it, a shadow falls on the LDR and the circuit gets activated and produce a pleasant sound through the buzzer.

This electronic eye circuit uses NOT gate from CMOS I.C CD 4049. CD 4049 contains 6 independent NOT gate in one package; we have used here (a) one only. NOT gate output goes high(1) when the input pin 3 is at lower then 1/3rd level of the supply voltage. Conversely the output goes low (0) when it is above 1/3rd level. So small change in the voltage of pin-2 is enough to change the level of output (pin-3) from 1 to 0 and 0 to 1. The output has only two states high and low and can not remain in any intermediate stage. It is powered by a 9V battery for portable use. The circuit is economic in power consumption. Pin 1 is connected to the positive supply and pin 8 is grounded.

To detect the present of an object we have used LDR and a source of light. LDR is a special type of resistance whose value depends on the brightness of the light which is falling on it. It has resistance of about 1 mega ohm when in total darkness, but a resistance of only about 5k ohms when brightness illuminated. It responds to a large part of light spectrum.

We have made a potential divider circuit with LDR and 220 KΩ resistance connected in series. We know that voltage is directly proportional to conductance so more voltage we will get from this divider when LDR is getting light and low voltage in darkness. This divided voltage is given to input of NOT gate.

As soon as LDR gets dark the voltage of input not gate Touch Switch

Fire Alarm

NAND Gate

Part List

Transistor = BC548 or any general purpose NPN Transistor will work. Dynamo

Consider a coil of fine insulated wire wound on a plastic or cardboard tube. Connect the ends of the coil to a DC milliammeter or galvanometer (for demonstration purposes!). A center-zero meter is preferred for this demonstration. Now take a bar magnet and thrust the magnet into the coil. The meter will deflect. Now withdraw the magnet. The meter deflects the other way. As we insert and withdraw the magnet, the meter deflects from one side to the other. With the magnet stationary, the meter reads zero. What’s happening? We see that when the magnet is moving, a current is induced in the coil. The moving magnetic field, from the moving magnet, cuts the conductors forming the coil.

PREVIOUS POST: Electronic Eye

NEXT POST: Heat SensorSolar Cell

The circuit illustrated below is used as Solar Cell. You can get plate from your old faulty solar calculator. Carefully dissemble plate with out tearing its 2 wire. Connect both wire to a LED through a switch. When Solar Plate is kept in sunlight and switched ON you will see LED glows .

Please make sure for the correct polarity of LED.

Theory :

When energy is added to pure silicon, for example in the form of heat, it can cause a few electrons to break free of their bonds and leave their atoms. A hole is left behind in each case. These electrons then wander randomly around the crystalline lattice looking for another hole to fall into. These electrons are called free carriers, and can carry electrical current

Solar Plate can be made by :

Step 1

Stain the Titanium Dioxide with the Natural Dye

Step 2

Coat the Counter Electrode

Step 3

Add the Electrolyte and Assemble the Finished Solar Cell

Musical Bell

This circuits uses very few component and gives melody sound. It uses 3 terminal IC UM66 and can be build small enough to be placed inside a greeting card and operatedFM Transmitter

Image of FM TransmitterFM Transmitter

Image of FM Transmitter

Circuit Diagram of FM Transmitter

The circuit uses only single Transistor but good voice quality. This Circuit is very simple and uses few components. Main part of the circuit is RC ( Resistance Capacitor )circuit to produce RF at required Frequency band.

At FM receiver side Radio waves(oscillating magnetic lines) produces current in Arial. Which is further amplified, Demodulated and feed to a Speaker.

Part List

Capacitor :

10 Mfd, .01 Mfd, .001Mfd, 2.2pf, 4pf, 5pf, 27pf, 68pf

Resistance :

3.3K, 2.7K, 3.9K, 220 Ohms

Transistor=494B

Mic = Condenser Mic

3V battery with Container, Switch

Arial

This Video explains how Radio waves are produced

PREVIOUS POST: Logic Gates

NEXT POST: Automatic Street Light

Using Fuse Tube Light

The circuit illustrated below can RE use your thrown tube light. A high DC voltage can glow a a weak florescent tube light. An used florescent tube gets black at one edge. Which indicates weakness. At such end Positive voltage should be applied and can be marked as anode and other clear end cathode can be marked for Negative voltage or electron will be supplied.

Please see circuit Diagram.For converting AC in to DC we have used a Rectifier Circuit. Choke Should be used in series with rectifier circuit for limiting current.Rectified voltage(DC) is applied to both end of the tube.

PREVIOUS POST: Musical Bell

NEXT POST: Telescope

Circuit Diagram of FM Transmitter

The circuit uses only single Transistor but good voice quality. This Circuit is very simple and uses few components. Main part of the circuit is RC ( Resistance Capacitor )circuit to produce RF at required Frequency band.

At FM receiver side Radio waves(oscillating magnetic lines) produces current in Arial. Which is further amplified, Demodulated and feed to a Speaker.

Part List

Capacitor :

10 Mfd, .01 Mfd, .001Mfd, 2.2pf, 4pf, 5pf, 27pf, 68pf

Resistance :

3.3K, 2.7K, 3.9K, 220 Ohms

Transistor=494B

Mic = Condenser Mic

3V battery with Container, Switch

Arial

This Video explains how Radio waves are produced

off a single 3V flat button cell.

There is not much to the circuit. The UM66 is connected to its supply and its output fed to a transistor for amplification. Any common speaker can be used or a “flat” piezoelectric tweeter like the one found in alarm wrist watches. If you use the piezo, then it can be connected directly between the output pin 1 and ground pin 3 without the transistor.

The UM66 looks like a transistor with 3 terminals. It is complete miniature tone generator with a tune. Now they come with wide variety of different tunes.

For amplification we have used a NPN transistor which is BC548. Here BC548 makes a common emitter circuit. For limiting the base current we have used a resistance of 220 Ohms so that transistor will not get damaged by excess current.

Circuit Diagram of Musical Bell

PROCEDURE :

1. Draw circuit diagram on ply board and make hole with compass or broader for component pin insertion.

2. Identify emitter base collector of transistor and pin no. of IC UM66

3. Solder all parts according to the circuit. You will need soldering iron, Soldering flux and flexible wire.

4. Make sure all points are well soldered according to the Circuit Diagram and no dry solders. Wrong connection of IC may heat up and get damage.

5. After loading battery power ON the circuit. Now you can check the function of the project.

PREVIOUS POST: Rain Alarm

NEXT POST: Using Fuse Tube Light

LED (Light Emitting Diode) any Color except white.

Resistance = 10 K,270 k and 220 ohms.

3 Pcs Slide Switch

1 battery container for connecting 2 cell.

This circuit works well and consumes only 3 Volt.

Circuit Diagram of NAND GATE is given below.

Other logic gate such as NOT,AND, OR can also be designed by NAND, NOR Gates.You can use NAND, NOR as Universal gate.

See my next project. I have made AND, OR, NOT by using NAND Logic gate IC CD4011.

MP3 Player Kit

MP3 Player with Digital FM Radio Receiver

This circuit project is used for playing mp3 files from a memory chip, card reader or from a pen drive. Same circuit is also used for receiving telecast of FM band Radio with digital Display of frequency.

You will need MP3 Kit.

Kit include MP3 Card with Digital Display, USB port, Remote Control and connecting cables as shown in the fig below :

Four Tone Siren

FOUR TONE SIREN

UM3561 PROJECT CIRCUIT

UM3561 IC includes oscillator and selector circuits so few external component is used for construction of four tone siren.

The UM3561 contains programmed mask ROM to simulate siren sound. Power consumption of IC is low.It is powered by 3 Volt. One NPN Transistor is used for amplification of audio signal.

Circuit Diagram of Four Tone Siren

Part List :

IC UM3561

Resistance = 220 Ohms

Condenser 100Mfd

Transistor BC548

Battery Container 3V

Switches

PREVIOUS POST: Touch Switch

NEXT POST: Fire Alarm

You will need IR (Infra Red) Sensor which is commonly used in TV, DVD Player etc.

Robot Kit

Microcontroller based Project

As you know our site is based on Simple Electronics Project Circuit. But to achieve higher performance, (Engineering Level Project) now day’s electronics kits uses Advance Digital Circuit for high quality output.

Advance Project requires a circuit which can be programmed for different work and can be capable of sensing from surroundings by using all types of sensors or module available in the market. i.e. (Remote Sensor, Keyboard,LCD Panel, Ultra sound sensor, RF Data, Sound, Gas Sensor, Memory chip reader/writer, humidity sensor etc.)

Among many I found two advance types of Kits which will be best for Hobby Circuit and also can be used in Robot.

This two Advance Controller Kits are PICAXE and ARDUINO which you can use in almost all Electronics Project. Among both arduino is more advance.

PICAXE Kits PICAXE microcontrollers are exciting, low-cost, re-programmable chips that can be used as low-cost ‘brains’ in many kinds of electronic project.

Among different PIC chips, I recommend PICAXE 28×1. PICAXE needs Serial port for programming which can be directly connected to computer on the other hand Arduino supports USB which is commonly used everywhere.

PICAXE is programmed using a simple BASIC language or via the Logicator flowcharting software. Windows Mac and Linux are all supported by the free BASIC software which can be downloaded from www.picaxe.com

Arduino Uno is a new version 2011 microcontroller board based on the ATmega328. It has 14 digital input/output pins (of which 6 can be used as PWM outputs), 6 analog inputs, a 16 MHz crystal oscillator, a USB connection, a power jack, an ICSP header, and a reset button. It contains everything needed to support the microcontroller; simply connect it to a computer with a USB cable or power it with a AC-to-DC adapter or battery to get started.

Benefits:

*Contains everything required to support the microcontroller

*User friendly USB connection (or can be powered with a AC-DC adapter or a battery)

*14 digital input/output pins (6 of these can be utilised as PWM outputs)

*6 analog inputs

*16 MHz crystal oscillator

*USB connection, and power jack for 9V supply

*ICSP header

*Reset button

PREVIOUS POST: MP3 Player Kit

You will need Power Supply Source of 5V. You can use Voltage Regulator IC7805 if source voltage is greater then 6 Volt.

Power Supply Source can be 4Pcs chargeable Pencil Battery for portable use or for mains 230V Supply you have to use a 9V Transformer with rectifier circuit also known as adapter plus a Regulator IC 7805 as shown in the fig below.

You can also use SMPS type adapter of 5 Volt 1A. which is commonly available for mini cd Player or ipod charger. In that case you don’t need to use Regulator IC.

Half Amp current is enough if you are not using an Amplifier Circuit.

If you wish to use Speaker then you have to use Amplifier Circuit.

For Amplification you can use 6283 Circuit.

For Simple Circuit new Project we have omitted panel button which is marked K1,K2,K3 and K4 on PCB. All function is included in remote.

Circuit Diagram of this project will be available soon.

6283 Amplifier Circuit will be available soon.

Circuit Diagram of low cost refrigerator will be available soon.

PREVIOUS POST: Automatic Street Light

IC CD4011 Contains 4 NAND Gates so I used 2 IC in this project. Other components are :-

3 Pc of 470 ohms, 3pcs led, 5 pcs mini SPDT Switch, 1 Rocker Switch, 9V Battery with Snap, Varo board IC type.

NEXT POST: Touch Switch

Here is a simple circuit which can be used as a Fire Alarm. 3 Volt is enough to operate. There is not much to the circuit. The IC UM66 is connected to its supply and its output fed to a transistor for amplification.

UM66 is a complete miniature tone generator with a ROM of 64 notes, oscillator and a preamplifier. For amplification we have used a NPN transistor which is BC548. Here BC548 makes a common emitter circuit. For limiting the base current we have used a resistance of 220 Ohms so that transistor will not get damaged even if IC is wrong connected.

For heat sensor we have used tube light starter in place of manual switch. In a starter there is a metal plate and a pin with small gap. When starter gets heated then metal plate of starter expands and get in contact with the pin and circuit is completed and we get audio from speaker. For fast sensing we can use starter without its glass body by carefully breaking glass cover.

Circuit Diagram of Fire Alarm

PREVIOUS POST: Four Tone Siren

NEXT POST: Burglar Alarm

Same Circuit can be use as Touch Alarm, Rain Alarm etc

THEAFS ARE ATTRACTED TO EXPENSIVE THINGS WHEN THEY COME IN OUR HOUSES. WE CAN PROTECT OUR PRODUCT OR THING BY MAKING THEM TOUCH PROOF OR WE CAN STOP ANY UNIDENTIFIED PERSONS ENTRY IN OUR HOUSE BY MAKING DOOR AND WINDOW TOUCH PROOF.THIS CIRCUIT ALERT US WHEN ANY THEAF COME TO STOLE PRODUCTS FROM OUR HOUSE OR TOUCH ANY METALLIC THING AT DOOR / WINDOW OR IN SIDE . WE CAN USE THIS CERCUIT TO PROTECT OUR CAR OR BIKE BY MAKING THEM TOUCH PROOF.

AS WE HAVE DISCRIBE ABOVE THIS PRODUCT GIVE ALARM WHEN ANY HUMAN BODY TOUCH ANY OF THE METTALIC THING WHICH ARE PROTECTED BY THIS CIRCUIT. THIS PROJECT IS WORKING ON TWO TRANSISTORS

WHICH MAKE COMPLIMENTORY PAIR DIRECT COUPLED AMPLIFIER. THIS CIRCUIT BASICALLY A AUDIO OSILATOR FOR OSILATION WE USE COLLECTOR OF TRANSISTOR BC558 WHICH IS CONNECTED TO THE BASE OF TRANSISTOR BC 548 VIA RESISTANCE 18 K .01 or .02 MFD CAPACITOR . TRANSISTOR BC-548 IS WORKING AS A PREAMPLIFIER.

WHEN ANY HUMAN BODY TOUCH THE TOUCH SENSOR WHICH IS CONNECTED TO BASE OF TRANSISTOR BC-548. THIS TRANSISTOR CONDUCT WITH HUMAN SKIN CONDUCTANCE . WHEN TRANSISTOR BC-548 START CONDUCTING IT’S FORCED TO Logic Gates

Simple Logic Processor Circuit or you can say a simple computer.

Picture of our Logic Gate Project

We have made three logic gate in our project. 1st is OR Gate, 2nd is AND Gate and 3rd one is NOT Gate. LED’s as indicator glows to show output level high or low.Here we have kept glow as “1″ and dark for “0″ This circuit uses Diode and Transistor for switching.

3V supply is enough for the circuit.

Component List :

LED Red or Green – 3Pcs

Switch mini SPST or slide Switch – 5 Pcs

Diode 4007 – 2Pcs

Transistor BC558 – 3Pcs

Resistance 1 K – 3 Pcs

Resistance 220 Ohms – 1 Pc

Battery Container 3V

I have made another Project which include AND & NOT Gate. See picture below.

For AND gate I have used 2 NPN Transistor in series which is BC548 whose each base is driven by switch and resistance of 10K ohms. Output is connected to a LED through a resistance of 220 ohms.

By combining both the gate you can make NAND logic gate. Circuit diagram given below.

Now days logic gate IC is used instead of basic circuit. Two Type available TTL and CMOS.

OR Gate =

AND Gate =

NOT Gate = CD4049, 7404

NAND Gate = CD4011, 7400

PREVIOUS POST: Electronic Letter Box

NEXT POST: FM Transmitter

• SENSOR CIRCUIT

o ELECTRONIC LETTER BOX

o CLAP SWITCH

o RAIN ALARM

o HEAT SENSOR

o AUTOMATIC STREET LIGHT

o ELECTRONIC EYE

o BURGLAR ALARM

o TOUCH SWITCH

o FIRE ALARM

• DIGITAL CIRCUIT

o NAND GATE

o LOGIC GATES

o MP3 PLAYER WITH FM

o ROBOT CIRCUIT

• POWER SUPPLY CIRCUITS :

o DYNAMO

o SOLAR CELL

• MUSICAL CIRCUIT

o MUSICAL BELL

o FOUR TONE SIREN

• MISC PROJECT

o FM TRANSMITTER

o TELESCOPE

o USING FUSE TUBE LIGHT

•

TRANSISTOR BC558 TO START CONDUCTING . SO WE GET ALARM SOUND FROM SPEAKER. WHEN WE TAKE BACK OUR HAND THEN DOES NOT CONNECTED TO BASE OF TRANSISTOR BC-548 . SO IT’S DOES NOT CONDUCT WE DO NOT GET THE ALARM SOUND.

Circuit Diagram of Touch Switch / Touch Alarm / Rain Alarm

PREVIOUS POST: NAND Gate

NEXT POST: Four Tone Siren

drops 1/3rd of the supply voltage and pin 2 gets high and LED or buzzer which is connected to the output gets activated.

Advantage of using Logic gate is that data can be easily send to other digital interface device ie one can easily fed data to computer using parallel port or for further processing .

Circuit Diagram of Electronic Eye

Part List :

potential divider circuit with LDR and 100K variable resistance connected in series. We know that voltage is directly proportional to conductance so more voltage we will get from this divider when LDR is getting light and low voltage in darkness. This divided voltage is given to pin 2 of IC 555. Variable resistance is so adjusted that it crosses potential of 1/3rd in brightness and fall below 1/3rd in darkness.

Sensitiveness can be adjusted by this variable resistance. As soon as LDR gets dark the voltage of pin 2 drops1/3rd of the supply voltage and pin 3 gets high and LED or buzzer which is connected to the output gets activated.

Circuit Diagram of Automatic Street Light

Component used

9v Battery with strip

Switch

L.D.R (Light Depending Resistance)

I.C NE555 with Base

L.E.D (Light Emitting Diode) 3 to 6 pieces.

Variable Resistance of 47 Kilo ohms

P.C.B (Printed Circuit Board of 555 or Vero board.

COMPONENTS :

a) Battery: For 9v power supply we can use 6pcs dry cell or 6F22 9v single piece battery.

b)Switch:Any general purpose switch can be used. Switch is used as circuit breaker.

c) L.D.R: (Light Depending Resistance)

it is a special type of resistance whose value depends on the brightness of light which is falling on it. It has resistance of about 1mega ohm when in total darkness, but a resistance of only about 5k ohms when brightness illuminated. It responds to a large part of light spectrum.

d) L.E.D:

A diode is a component that only allows electricity to flow one way. It can be

thought as a sort of one way street for electrons. Because of this characteristic, diode are used to transform or rectify AC voltage into a DC voltage. Diodes have two connections, an

anode and a cathode. The cathode is the end on the schematic with the point of the triangle pointing towards a line. In other words, the triangle points toward

that cathode. The anode is, of course, the opposite end. Current flows from the anode to the cathode. Light emitting diodes, or LEDs, differ from regular diodes in that when a voltage is applied, they emit light. This light can be red (most common), green, yellow, orange, blue (not very common), or infa red. LEDs are used as indicators, transmitters, etc. Most likely, a LED will never burn out like a regular lamp will and requires many times less current. Because LEDs act like regular diodes

and will form a short if connected between + and -, a current limiting resistor is used to prevent that very thing. LEDs may or may not be drawn with the circle surrounding them.

e) Variable resistance:(Potentiometer)

Resistors are one of the most common electronic components. A resistor is a device that limits, or resists current. The current limiting ability or resistance is measured in ohms, represented by the Greek symbol Omega. Variable resistors (also called potentiometers or just “pots”) are resistors that have a variable resistance. You adjust the resistance by turning a shaft. This shaft moves a wiper across the actual resistor element. By changing the amounts of resistor between the wiper connection and the connection (s) to the resistor element, you can change the resistance. You will often see the resistance of resistors written with K (kilohms) after the number value. This means that there are that many thousands of ohms. For example, 1K is 1000 ohm,2K is 2000 ohm, 3.3K is 3300 ohm, etc. You may also see the suffix M (mega ohms). This simply means million. Resistors are also rated by their power handling capability. This is the amount of heat the resistor can take before it is destroyed. The power capability is measured in W (watts) Common wattages for variable

resistors are 1/8W, 1/4W, 1/2W and 1W. Anything of a higher wattage is referred to as a rheostat

f) PCB (Printed Circuit Board)

with the help of P.C.B it is easy to assemble circuit with neat and clean end products. P.C.B is made of Bakelite with surface pasted with copper track-layout. For each components leg, hole is made.

Connection pin is passed through the hole and is soldered.

WORKING:

When light falls on the LDR then its resistance decreases which results in increase of the voltage at pin 2 of the IC 555. IC 555 has got comparator inbuilt, which compares between the input voltage from pin2 and 1/3rd of the power supply voltage. When input falls below 1/3rd then output is set high otherwise it is set low. Since in

brightness, input voltage rises so we

obtain no positive voltage at output of pin 3 to drive relay or LED, besides in poor light condition we get output to energize.

Precautions:

a) LDR used should be sensitive.

Before using in the circuit it should be tested with multimeter.

b) I.C should not be heated too much while soldering, can destroy the I.C. For safety and easy to replace, use of I.C base is suggested. While placing the I.C pin no 1 should be made sure at right hole.

c) Opposite polarity of battery can destroy I.C so please check the polarity before switching ON the circuit. One should use diode in series with switch for safety since diode allows flowing current in one direction only.

d) L.E.D glows in forward bias only so incorrect polarity of L.E.D will not glow. Out put voltage of our project is 7.3 volt therefore 4 LED in series can be easily used with out resistance.

e) Each component should be soldered neat and clean. We should check for any dry soldered.

f) LDR should be so adjusted that it should not get light from streetlight itself.

PREVIOUS POST: FM Transmitter

NEXT POST: MP3 Player Kit

• SENSOR CIRCUIT

o ELECTRONIC LETTER BOX

o CLAP SWITCH

o RAIN ALARM

o HEAT SENSOR

o AUTOMATIC STREET LIGHT

o ELECTRONIC EYE

o BURGLAR ALARM

o TOUCH SWITCH

o FIRE ALARM

• DIGITAL CIRCUIT

o NAND GATE

o LOGIC GATES

o MP3 PLAYER WITH FM

o ROBOT CIRCUIT

• POWER SUPPLY CIRCUITS :

o DYNAMO

o SOLAR CELL

• MUSICAL CIRCUIT

o MUSICAL BELL

o FOUR TONE SIREN

• MISC PROJECT

o FM TRANSMITTER

o TELESCOPE

o USING FUSE TUBE LIGHT

•

Current Sensing

Current sensing is as it says - sensing the amount of current in use by a particular circuit or device. If you want to know the amount of power being used for any robot component, current sensing is the way to go.

Applications

Current sensing is not a typical application in robotics. Most robots would never need a current sensing ability. Current sensing is a way for a robot to measure it's internal state and rarely required to explore the outside world. It is useful for a robot builder to better understand power use of the various components within a robot. Sensing can be done for DC motors, circuits, or servos to measure actuator power requirements. It can be done for things like microcontrollers to measure power performance in different situations. It can be useful for things likerobot battery monitors. And lastly, robot hand grasp detection devices and collision detection. For example, if the current use suddenly increases, that means a physical object is causing resistance.

Methods

There are several methods to sense current, each having its own advantages and disadvantages.

The easiest method is using a typical benchtop DC power supply.

Electronic Letter Box

To detect the present of letter we have used LDR and a source of light. LDR is a special type of resistance whose value depends on the brightness of the light which is falling on it. It has a resistance of about 1 megaohms when in total darkness, but a resistance of only about 2-5 k ohms when brightly illuminated. It responds to a large part of the light spectrum.

The source of light and LDR is so adjusted in the letter box that light will directly fall on the LDR but when letter is kept inside then it will block the beam of light and LDR will be under darkness.

We have made a potential divider circuit with LDR and 100 K variable resistance

connected in series. Voltage is directly proportional to conductance so more voltage we will get by this divider when LDR is getting light and low voltage in darkness. Divided voltage is given to pin 2nd of 555. As soon as LDR gets dark the voltage of the pin 2 drops 1/3 of the supply voltage and pin 3 gets high and LED glows.

The circuit illustrated below is used as an electronic letter box. When letter is kept in this box then a LED glows which indicates that letter is inside the Box.

This circuit uses a popular timer I.C which is 555. I.C 555 is connected as comparator with pin 6 connected with positive supply, the output goes high-1 when the trigger pin 2 is at lower than 1/3 level of the supply voltage. Conversely the output goes low-0 , when it is above 1/3 level. So small change in the voltage of pin 2 is enough to change the output of pin 3 from 1 to 0 and 0 to 1. The output has only two states high and low and can not remain in any intermediate stage. It is power by 9V battery for portable use. The circuit is economic in power consumption. Pin 4,6&8 is connected to the positive supply and pin 1 is grounded.

To detect the present of letter we have used LDR and a source of light. LDR is a special type of resistance whose value depends on the brightness of the light which is falling on it. It has a resistance of about 1 megaohms when in total darkness, but a resistance of only about 2-5 k ohms when brightly illuminated. It responds to a large part of the light spectrum.

The source of light and LDR is so adjusted in the letter box that light will directly fall on the LDR but when letter is kept inside then it will block the beam of light and LDR will be under darkness.

We have made a potential divider circuit with LDR and 100 K variable resistance

connected in series. Voltage is directly proportional to conductance so more voltage we will get by this divider when LDR is getting light and low voltage in darkness. Divided voltage is given to pin 2nd of 555. As soon as LDR gets dark the voltage of the pin 2 drops 1/3 of the supply voltage and pin 3 gets high and LED glows.

This device is somewhat expensive as it ranges in the hundreds, but they are very common and you can easily find one available in any typical university lab. These devices are a must for any electrical engineer or robot builder. Operation of this device should be straigtforward. Apply a voltage to your component, and it will quickly give a readout of the current you are drawing. Although this takes seconds and little effort to do, there are a few disadvantages to this method.

The first disadvantage is that it is not highly accurate. Usually they can only measure in increments rounded off to the nearest 10mA. This is fine for high powered applications where an extra 5mA does not matter, but for low current draw devices this can be an issue. The next disadvantage is timing. A benchtop power supplies only takes current measurements in set periods of time - usually 3 times a second. If your device draws a steady current over time this is not a problem. But if for example your device ramps from 0 to 3 amps five times a second, the current reading you get will not be accurate. The last major disadvantage is that there is no data logging ability - therefore you cannot analyze any complex current draw data on a computer.

The second method is using a digital multimeter. Heat Sensor

Here is a simple circuit which can be used as a heat sensor. In the following circuit diagram thermistor and 100 Ohms resistance is connected in series and makes a potential devider circuit . If thermistor is of N.T.C (Negative temperature Coefficient ) type then after heating the thermistor its resistance decreases so more current flows through the thermistor and 100 Ohms resistance and we get more voltage at junction of thermistor and resistance. Suppose after heating 110 ohms thermistor its resistance value become 90 Ohms.then according to potential devider circuit the voltage across one resistor equals the ratio of that resistor’s value and the sum of resistances times the voltage across the series combination. This concept is so pervasive it has a name: voltage divider. The input-output relationship for this system, found in this particular case by voltage divider, takes the form of a ratio of the output voltage to the input voltage.

This output voltage is applied to a NPN transistor through a resistance. Emitter voltage is maintain at 4.7 volt with a help of Zener diode.

This voltage we will use as compare voltage. Transistor conducts when base voltage is greater than emitter voltage. Transistor conducts as it gets more than 4.7 base Voltage and circuit is completed through buzzer and it gives Sound.

Heat Sensor Circuit Diagram

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The digital multimeter is another commonly available device capable of analyzing many different characteristics of your circuit - voltage, current, capacitance, resistance, temperature, frequency, etc. If you do not already have one, you definitely need one to make a robot. It would be like cooking without heat if you didnt have one . . . For cost, they range in price from around $10 to about $100. The price depends on features and accuracy. To measure current, all you do is connect your two leads in series with one of your power source wires. But again, there are disadvantages to this method.

Like the benchtop power supplies, digital multimeters suffer timing issues. However, accuracy is usually an extra one or two decimal places better. Good enough for most applications. As for data logging, several available multimeters actually have computer linkup cables so that you may record current data to process later.

The last method is using a chip called a Current Sense IC.

This ~$5 chip, using a really tiny resistor and a built in high gain amplifier, outputs a voltage in proportion to the current passing through it. Put the chip in series with what you want to measure, and connect the output to a data logging device such as a microcontroller. The microcontroller can print out data to hyperterminal on your computer, and from there you can transfer it to any data analyzing program you wish (like Excel). Clap SwitchRain Alarm

GIVES BEEP WHEN WATER IS IN CONTACT WITH THE WIRE

Water is a conductor of electricity. When water is in contact with the probe then there is a flow of current which reaches to the base of Q1. Transistor Q1 is a NPN transistor which conducts. With the conduction of Q1 electron reaches to Q2 which is a PNP transistor .Q2 also conducts and current flows through the speaker. In a speaker there is inductive coil which causes motion in one direction and also produce induce current which is in opposite direction to the flow of current this induce current in the form of pulse flows through a capacitor, resistance and switches off Q1 and relax .this process repeats again and again till probe is in contact with water or we can say there is a oscillation in the circuit thus speaker diaphragm vibrates and gives a tone. Frequency of the circuit depends on the value of Speaker Coil impendence, Capacitor and Resistance Value.

Circuit Diagram of Rain Alarm

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Here is a Hobby Circuit for electronics hobbyists that can switch on & off a light, Fan, Radio etc. by the sound of clap.The sound of clap is received by a small microphone that is shown biased by resistor R1 in the circuit. The microphone changes sound wave in to electrical wave which is further amplified by Q1.Transistor Q1 is used as common emitter circuit to amplify weak signals received by the microphone. Amplified output from the collector of transistor Q1 is then feed to the Bistable Multivibrator circuit also known as flip-flop.

Flip flop circuit is made by using 2 Transistor, in our circuit Q2&Q3. In a flip-flop circuit, at a time only one transistor conduct and other cut off and when it gets a trigger pulse from outside source then first transistor is cutoff and 2ndtransistor conducts. Thus output of transistor is either logic-0 or logic-1 and it remains in one state 0 or 1 until it gets trigger pulse from outer source.

The pulse of clap which is a trigger for flip-flop which makes changes to the output which is complementary (reverse). Output of flip-flop which is in the low current form is unable to drive relay directly so we have used a current amplifier circuit by using Q4 which is a common emitter circuit. Output of Q4 is connected to a Relay (Electromagnetic switch) which works like a mechanical switch and it becomes easy for connecting other electrical appliance.

The relay contact is connected to the power line and hence turns on/off any electrical appliance connected all the way through relay.

Circuit Diagram of Clap Switch

How Clap Switch Works

Part List:

Resistors

R1=15KΩ, R5,R6=1.5KΩ

R2,R11,R12=2.2MΩ, R13=2.2KΩ

R3=270KΩ, R4=3.3KΩ

R7,R8=10KΩ, R9,R10=27KΩ

Capacitors

C1=1000µf/16v

C2=.01µf,C3,C4=.047µf

Semiconductor

Q1,Q2,Q3= BC548

D2,D3,D4= IN 4148

D1,D5=IN 4007, Q4=BC368

Misc

T1=12v/500mA Transformer

Mic= Condenser Microphone

K1= 12V Relay, B1= Bulb or Load

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• SENSOR CIRCUIT

o ELECTRONIC LETTER BOX

o CLAP SWITCH

o RAIN ALARM

o HEAT SENSOR

o AUTOMATIC STREET LIGHT

o ELECTRONIC EYE

o BURGLAR ALARM

o TOUCH SWITCH

o FIRE ALARM

• DIGITAL CIRCUIT

o NAND GATE

o LOGIC GATES

o MP3 PLAYER WITH FM

o ROBOT CIRCUIT

• POWER SUPPLY CIRCUITS :

o DYNAMO

o SOLAR CELL

• MUSICAL CIRCUIT

o MUSICAL BELL

o FOUR TONE SIREN

• MISC PROJECT

o FM TRANSMITTER

o TELESCOPE

o USING FUSE TUBE LIGHT

•

This particular schematic below (click for the full expanded circuit) can measure current use of a servo. But it can easily measure current from any other device with no modification - and even multiple items simultaneously too! The capacitor is optional as it acts as a voltage buffer, ensuring maximum continuous current.

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