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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