Saturday, 25 October 2014

Logic Gates

Logic gates are the building blocks of digital technology. It is a mechanical, optical, or electronic system that performs a logical operation on an input signal. Truth tables are used to help show the function of a logic gate.
Logic Gate workingSimple Logic Processor Circuit or you can say a simple computer.
Logic Gate Project
                      Picture of our Logic Gate Project
Logic gates are primarily implemented using diodes or transistors acting as electronic switches. We have made three basic logic gate using Diode and NPN Transistor. OR Gate, AND Gate and 3rd is NOT Gate. LED’s as indicator used to show output level high(1) or low(0). 3V power supply is enough for the circuit.
Component List :
LED Red or Green – 3Pcs
Mini SPST or slide Switch – 5 Pcs
Diode 4007 – 2Pcs
Transistor BC548 – 3Pcs
Resistance 100 Ohms, 220 Ohms, 1K – 1 Pc each
Resistance 10 K – 3 Pcs
Battery Container 3V
1. For AND gate I have used 2 NPN Transistor (BC548) in series whose each base is driven by separate switch and resistance. Output is connected to a LED through a resistance of 220 ohms.
2. NOT gate also known as inverter  I have used single NPN transistor as shunt. In normal condition current flows through 220 ohms resistance and LED which results glow but when switch is in ON position then transistor conducts and current flows throw it rather than LED because of low resistance. In other words at ON position there is a voltage drop at output because of transistor conductance.
3. In OR Gate I have used 2 Diodes in parallel
By combining both the gate (AND Gate + NOT Gate) you can make NAND logic gate.
You may also be interested in NOR Gate which is made by combining OR Gate and Not Gate
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