ELECTRONIC CALCULATOR

hello  friends  today I am gonna  telling  you  about  some  easy  and valuable  electronics projects for  school and  college  practical 

An electronic calculator is a device used to calculate problems in science, engineering and mathematics.  Here we present a microcontroller-based electronic calculator.  This calculator can perform addition, subtraction, multiplication, division, reciprocal, square root and exponentiation for positive and negative real numbers.
 
Fig.  1 shows the circuit diagram of microcontroller - based electronic calculator .Microcontroller AT89052 is at the heart of this calculator. The AT89C52 is a low-power , high- performance CMOS 8-bit microcomputer with 8k bytes of Flash programmable and erasable read only memory (EPROM ) .  The AT89C52 provides standard features - 256 bytes of RAM , 32 input / output lines , three 16 - bit timers / counters , a six - vector two - level interrupt architecture , a full - duplex serial port , on - chip oscillator and clock circuitry.

System clock plays a significant role in the operation of the microcontroller .  A 12MHz quartz crystal at pins 18 and 19 provides clock pulse to the microcontroller ( IC1) .  Power on reset is provided by electrolytic capacitor C3 and resistor R2 .  Switch S1 is used for manual reset .  Microcontroller port pins P14 through P1.7 and 13 2 through P3.7 are used to form the keypad matrix .  Port 12 is connected with the seven - segment display , Port P2 provides segment data to glow the LED segments of the seven - segment display .  Eight 100 - ohm resistors are used to limit the current through LEDs segment of seven - segment display .  Port PO is pulled high with 10k resistor network RNW1 .  

Fig1-Circuit Diagram

Microcontroller port pins P0.0 through P0.7 drive the DIS1 through DIS8 with the help of transistors T1 through T8 , respectively .  Microcontroller port pin P0.0 goes low to drive transistor T1 into saturation and provides supply to common - anode pin 3 of DIS1 .  Similarly , transistors T2 through T8 drive common - anode of seven - segment display pin 3 of DIS2 through DIS8 , respectively .  Microcontroller provides the segment data and display - enable signal simultaneously in time division multiplexed mode for displaying a particular number on the seven - segment display unit .  Segment data and display-enable pulse for display are refreshed after every few  millisecond delay. thus the display  appears to be continuous even though it light up one by one.

The 230V , 50HZ AC mains is stepped down by transformer X1 to de liver a secondary output of 9V , 500mA . The transformer output is rectified by a full - wave rectifier comprising diodes D1 through D4 , filtered by capacitor C1 and regulated by IC 7805 ( IC2 ) .  The Capacitor C2 bypasses the ripples present in the regulated supply.  LED1 acts as the power indicator and R1 limits the current through LED1 .  

Assemble the circuit on a PCB as it minimizes time and assembly errors .  Carefully assemble the components and double - check for any overlooked errors. 

PARTS LIST

Semiconductors : 

IC1 -    AT89C52 microcontroller 

IC2 -    7805 , 5V regulator 

T1 - T8 - BC557 pnp transistor 

DIS1 - DIS8 - LTS542 common anode seven - segment display 

D1 - D4 - 1N4007 rectifier diode 

LED1 - 5mm LED 

RESIST0RS(1/4-WATT+-5%carbon)

R1 - 470 ohm 

R2 - 10 - kilo - ohm 

R3 - R10 - 1 - kilo - ohm 

R11 - R18 - 100 - ohm 

RNW1 - 10 - kilo - ohm resistor network 

Capacitors : 

C1 -100 0uF  , 25V electrolytic

C2 - 0.1uF ceramic disk 

C3 - 10uF , 16V electrolytic

C4 , C5 - 22pF ceramic disk 

Miscellaneous : 

X1 - 230V AC primary to 9V , 500mA secondary transformer 

X^ tal  12MHz crystal 

S1 - S24- Push - to - on tactile switch 

Working of the calculator

The calculator works like any simple calculator available in the market.  The various digits and signs can be entered using numeric keys 0 to 9 and 00 , decimal point with ' dp ' and ' +/- for the sign of the number .  The display will show ' E ' if the answer is infinite . 

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                   VARIABLE OFF TIMER

hello  friends  today I am gonna  telling  you  about  some  easy  and valuable  electronics projects for  school and  college  practical

Here is a reliable , low - power , versatile and simple - to - wire preset off ' timer built around IC NE555 .  The specifications of this timer are : 

1. When the connected load is not in use , the timer automatically turns it ' off ' after the preset time , thus saving power. 

2. As the timer switches of the mains , it would not restart and run the load even if there is a power supply surge or power interruption .  

3. It's fail - safe because it won't switch on in the event of power resumption . 
Transformer X1 is used to step down the mains power supply from 220V AC to 12V AC , 300 mA.  Rectifier diodes D1 through D4 form the full wave bridge rectifier, which converts the 12V AC transformer output into DC.  Capacitor C1 removes ripples.  IC 7812 ( IC1 ) regulates the filtered supply to 12V DC 

IC 555 ( IC2 ) is wired as a one - shot timer whose time period can be easily calculated by T = 1.1xR1xC3 , where T ' is in seconds , R1 ' is in  ohms and ' C3 is in Farads .  Select a low - tolerance resistor R1 and low - leakage capacitor C3 if you want the timer to be accurate , Here , we have selected value of resistor R1 as 1 mega - ohm and value of capacitor C3 as 1000 pF , which amounts  to a time period ( T ) equal to 18 minutes approximately .  

Output of timer IC2 at pin 3 is connected to relay RL1 with the free wheeling diode D5 connected as shown in the circuit diagram .  The re- lay rating will depend on the load cur rent but it would be taken care of by keeping the relay coil current within 200 mA .  If it exceeds 200 mA , a driver transistor should be used to drive the relay .

The operation of the circuit is simple.  To start the timer, press switch S1 momentarily.  Relay RL1 gets energized immediately and switches on the load .  At the same time , LED1 glows to indicate that the timer is ' on .  ' At the end of 18 minutes , the output of the timer will go low and de-energize the relay , thus switching off the supply to load and timer.

This timer is useful for switching off water pumps used in houses to pump water from sump to the over head water tank , which depends on delivery rating of pump and the capacity of over - head tank .  In most of the cases, it takes approximately 18 minutes, hence the design for 18 minute fixed time.  The timer can be made variable by having fixed - value C3 and varying R1 , or vice versa .  Replacing R1 with a potmeter to set different switch - off timings can be one of the ways of implementing the application .

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     REMOTE CONTROL FOR TOY CAR

101％ working  project hello  friends  today I am gonna  telling  you  about  some  easy  and valuable  electronics projects for  school and  college  practical

Make any battery operated toy car remote controlled using this circuit . The circuit , consisting of an infrared transmitter - receiver pair , uses IR beam transmission to switch the toy car on or off . To operate the toy car , you need to hold the transmitter in your hand , keeping it pointed at the toy car which has the receiver fitted inside and simply press a switch provided on the transmitter . The transmitter works off 9V DC , while the receiver needs 6V DC. 

Fig . 1 shows the transmitter circuit . It is built around two BC558 transistors ( T1 and T2 ) , three BC548 transistors ( T3 , T4 and T5 ) , IR LED1 and a few discrete components . 

Fig . 2 shows the receiver circuit . It is built around IR receiver module TSOP1738 , two BC548 transistors ( T6 and 17 ) and a few discrete components . 

In the transmitter circuit , there are two astable multivibrators . The first , built around transistors T1 and T2 , produces a frequency of about 1.2 kHz . The second , built around transistors T3 and T4 , produces about 38 kHz . IR LED1 is used to transmit the 38kHz frequency 

In the receiver circuit , TSOP1738 receives the IR signal transmitted by IR LED1 of the transmitter circuit . The output of TSOP1738 is fed to transistor T6 via diode D1 . The amplified signal is further given to relay - driver transistor T7 . Relay RL1 energises to control the toy car .

Working of the circuit is simple . Initially , when no IR beam is falling on sensor TSOP1738 , the relay remains de-energised and the toy car doesn't move . When switch SI is pressed , the IR beam falls on TSOP1738 and its output goes low , Transistor T6 cuts off and transistor T7 conducts to energise relay RL1 and move the toy car 

Assemble both the circuits on separate PCBs . Enclose the transmitter PCB in a suitable cabinet , with IR LED1 affixed on the front side and switch S1 on the top of the cabinet . Keep the 9V battery inside the cabinet 
Enclose the receiver PCB inside the toy car , with TSOP1738 fitted such that the transmitted IR beam directly falls on it . Fix switch S2 on the body of the car and the relay inside the car . Use a V battery to operate the toy car receiver unit.

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HIGH RESISTANCE METER

              HING RESISTANCE METER

hello  friends  today I am gonna  telling  you  about  some  easy  and valuable  electronics projects for  school and  college  practical

HING RESISTANCE METER

This resistance meter can measure resistances up to 200 mega-ohms.  The value of the resistance is indicated on a T: linear meter scale (0-100 µA).  The operation of the circuit is based on sensing the voltage drop across a reference resistor.  The voltage sensing IC used here is a CMOS NAND gate (CD4011) whose high impedance makes it suitable for sensing the voltage drop across high resistances.

Connect the high resistance ( Rx ) to be measured in series with the reference resistor .  Apply a variable high voltage ( up to 100V ) at the other end of the unknown resistor ( Rx ) such that the voltage drop across the reference resistor ( Rref ) is equal to the threshold voltage ( Vthr ) of gate N3 of IC1 .

At this point , the voltage drop across the reference resistor ( Rref ) is sensed by gate N3 and its output goes low . Gate N4 inverts the low input to light up LED1 .  Now stop varying the high voltage. The resistance value is indicated on the meter directly.

Fig1;circuit diagram

At this time , the expression for the unknown resistance Rx by applying Ohm's law can be written as :

                          Rx =( V/vthr )Rref - Rref  ......... Eq.  (1) 

where ' V ' is the voltage applied across the Rx - Rref series combination and Vthr is the threshold voltage of gate N3 , which is also the voltage drop across the reference resistor  (Rref ) when LED1 glows . 
From Eq.  (1) , it is clear that the second term ( -Rref ) has to disappear in order to have a direct linear relation ship between V and Rx .  The equation can be rearranged as :

                             V =( Rx/Rref) Vthr + Vthr ......... Eq.  ( 2 ) 

This shows that by substracting Vthr from V , the relationship between V - Vthr and Rx becomes directly linear ( without any offset ) .  This substraction is acheived by using transistor BC557 ( T5 ) as the voltage is lower with potmeter VR6.Adjusting the potmeter at the emitter of BC557 produces the required offset voltage at the other end of the meter to nullify the second term ( thr ) such that the current through the meter is proportional to Rx .  

The high - voltage section consists of a high-voltage generator , which is basically an oscillator driven by step - down transformer X1 .  A 230V AC primary to 6V - 0-6V AC , 150mA secondary transformer is used here.  To derive the power supply , the transformer output is rectified by a bridge rectifier comprising diodes D3 through D6 , filtered by capacitor C2 and regulated by zener diodes ZDI , ZD2 and ZD3 ( 25V , 50V , 100V ) in combination with transistor BD115 ( T3 )  .  Diodes D7 and D8 ( each 1N4148 ) provide the required additional drop in voltage across the base - emitter junction of transistors T3 and T4 ( each BD115 ) .

The transformer can be wound on any ferrite core having dimensions of about 30x10x30 mm A primary - to secondary tum ratio of 25 : 350 will produce around 100V from 9V.  At 100V , the current through a 10 - mega - ohm resistor would be 10 A. This means a power requirement of VxI = 100x105 = 10 watts, which can be easily acheived using an ordinary 9V battery.  Most of the power is drawn by the regulating circuit and some by the meter .  

Presets VR3 ,VR4 and VR5 are used for calibration to get full- scale deflection ( FSD ) in the analogue ammeter . You can directly calibrate VR2 on a dial and use LED1 for indication .  The meter has been added for convenience and reliability .  It eliminates all ambiguities of any non - linearity associated with variable voltage at the emitter of T4.

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LASER COMMUNICATION SYSTEM

hello  friends  today I am gonna  telling  you  about  some  easy  and valuable  electronics projects for  school and  college  practical

This laser communication system transmits sound or music signals through a laser beam.  The intensity of the laser beam changes with the amplitude of the sound signal.  The variation in the intensity of the laser beam is converted into a variation in the voltage level by using a solar panel.  The voltage variation on the solar panel is amplified by a low-voltage audio power amplifier LM386 and reproduced by a speaker.  The maximum output of audio amplifier LM386 is 1 watt, while its voltage gain is 20 to 200.

The circuit consists of a transmitter and a receiver.  Both the transmitter and the receiver are built around IC LM386 , powered by a 9V battery 

Fig . 1 shows the transmitter circuit .  Here a laser diode ( LD1 ) with maxi mum operating voltage of around 2.6V DC and maximum operating current of 45 mA is used to transmit the audio signal .  The voltage divider network formed by R2 , R3 and VR3 keeps the voltage as well as the current for the laser diode in the safe region .

In place of the laser diode, you can also use a laser pointer.  Remove the battery from the laser pointer.  Extend two wires from terminals of LDI and connect them to the battery terminals of laser pointer .  The spring inside the laser pointer is the negative terminal.  The out put power of the laser pointer is 5 mW.  Take care while working with laser , as direct exposure to the laser beam can be hazardous to your eyes.  Point the laser beam to the solar panel.

Potmeter VR1 ( 10 - kilo - ohm ) is used to change the level of the input audio signal .  The audio input ( Vin ) is taken from the preamplifier output of the music system ( CD player , DVD player , etc ) .  Capacitor C2 and preset VR2 are used to vary the gain of the LM386 .  

Fig. 2 shows the receiver circuit.  The audio signal trans mitted by the laser diode ( LDI ) is received by the solar panel and amplified by IC2 .  The gain of the amplifier is fixed by capacitor C7 . Preset VR4 is used to change the signal level from the solar panel.  This signal is fed to input pin 3 of IC2 through coupling capacitor C5 so that the DC value from the solar panel can be eliminated .  The amplified output from IC2 is panel fed to the speaker , which plays the mu sic from the CD player connected at the input ( Vin ) of IC1.

Assemble the transmitter and receiver circuits on separate PCBs and enclose in suitable cabinets .  In the transmitter cabinet , fix two terminals for connecting the audio signal Fix switch S1 on the front panel and the laser diode ( LD1 or laser pointer ) to the rear side of the cabinet Keep the 9V battery inside the cabinet  

In the receiver cabinet , fix the solar panel to the rear side such that the transmitted beam directly falls on it .  Fix switch S2 on the front panel and the speaker to the rear side.  Keep the 9V battery inside the cabinet.  Refer Figs 3 and 4 for the laser pointer and solar panel.  

After assembling both the circuits , orient the laser diode ( or laser pointer ) such that the transmitted laser beam directly falls on the solar panel .  Use shielded wires for connecting to audio input and solar panel to reduce noise pickup .

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      LASER COMMUNICATION SYSTEM

hello  friends  today I am gonna  telling  you  about  some  easy  and valuable  electronics projects for  school and  college  practical

This laser communication system transmits sound or music signals through a laser beam.  The intensity of the laser beam changes with the amplitude of the sound signal.  The variation in the intensity of the laser beam is converted into a variation in the voltage level by using a solar panel.  The voltage variation on the solar panel is amplified by a low-voltage audio power amplifier LM386 and reproduced by a speaker.  The maximum output of audio amplifier LM386 is 1 watt, while its voltage gain is 20 to 200.

The circuit consists of a transmitter and a receiver.  Both the transmitter and the receiver are built around IC LM386 , powered by a 9V battery 

Fig . 1 shows the transmitter circuit .  Here a laser diode ( LD1 ) with maxi mum operating voltage of around 2.6V DC and maximum operating current of 45 mA is used to transmit the audio signal .  The voltage divider network formed by R2 , R3 and VR3 keeps the voltage as well as the current for the laser diode in the safe region .

In place of the laser diode, you can also use a laser pointer.  Remove the battery from the laser pointer.  Extend two wires from terminals of LDI and connect them to the battery terminals of laser pointer .  The spring inside the laser pointer is the negative terminal.  The out put power of the laser pointer is 5 mW.  Take care while working with laser , as direct exposure to the laser beam can be hazardous to your eyes.  Point the laser beam to the solar panel.

Potmeter VR1 ( 10 - kilo - ohm ) is used to change the level of the input audio signal .  The audio input ( Vin ) is taken from the preamplifier output of the music system ( CD player , DVD player , etc ) .  Capacitor C2 and preset VR2 are used to vary the gain of the LM386 .  

Fig. 2 shows the receiver circuit.  The audio signal trans mitted by the laser diode ( LDI ) is received by the solar panel and amplified by IC2 .  The gain of the amplifier is fixed by capacitor C7 . Preset VR4 is used to change the signal level from the solar panel.  This signal is fed to input pin 3 of IC2 through coupling capacitor C5 so that the DC value from the solar panel can be eliminated .  The amplified output from IC2 is panel fed to the speaker , which plays the mu sic from the CD player connected at the input ( Vin ) of IC1.

Assemble the transmitter and receiver circuits on separate PCBs and enclose in suitable cabinets .  In the transmitter cabinet , fix two terminals for connecting the audio signal Fix switch S1 on the front panel and the laser diode ( LD1 or laser pointer ) to the rear side of the cabinet Keep the 9V battery inside the cabinet  

In the receiver cabinet , fix the solar panel to the rear side such that the transmitted beam directly falls on it .  Fix switch S2 on the front panel and the speaker to the rear side.  Keep the 9V battery inside the cabinet.  Refer Figs 3 and 4 for the laser pointer and solar panel.  

After assembling both the circuits , orient the laser diode ( or laser pointer ) such that the transmitted laser beam directly falls on the solar panel .  Use shielded wires for connecting to audio input and solar panel to reduce noise pickup .

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DOOR HALF OPEN ALERT PROJECT

             DOOR HALF OPEN ALERT 

hello  friends  today I am gonna  telling  you  about  some  easy  and valuable  electronics projects for  school and  college  practical

Have you ever accidentally left your front door half open and one of your pets or your little one ran away?  Here is the smart solution to this problem. This circuit alerts you every ten seconds that your door is open.  

The circuit is based on the popular 14 - stage ripple - carry binary counter IC CD4060 and a few discrete components.  The counter built around IC CD4060 advances by one on the negative transition of each clock pulse.  It is reset (which means all of its outputs go low) by applying a high pulse at its reset input pin 12 through switch S1 independent of clock.  A normally - closed (N / C) push - to - off switch S1 is used as the door sensor 

Working of the circuit is simple.  When the door is closed , the switch S1 opens as per the mechanical arrangement and reset pin 12 goes high .  The oscillator circuit built around resistor R2 and capacitor C2 stops oscillating Piezobuzzer PZ1 doesn't sound as out puts Q7 and 13 remain low 

Fig1; circuit diagram

when the door is opened , switch S1 closes and reset pin 12 goes low .The oscillator starts oscillating and after a short delay of about 10 seconds , the  piezobuzzer  ( PZ1 ) starts giving 10 - second long beeps every 10 seconds The beep duration of the buzzer can be varied by changing the values ​​of timing components C2 or R2 

Assemble  the  circuit on a general purpose PCB and enclose in a plastic cabinet .  Mount the cabinet on the door frame and door switch S1 near the handle lock such that when the door is closed the switch (S1) opens.  For powering the circuit, use an appropriate 3V battery pack.

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