Apparatus:
CRP123 power supply (6V), variable resistor (100k), NAND gate, buzzer bread board.
Theory:
NAND gate is the combination of AND gate followed by NOT gate (inverter). The of NAND gate is high of anyone or more of the inputs are low. The symbol for AND gate is shown in figure.
A small circle with AND gate represents NOT gate.
Boolean expression for NAND gate is
The truth table for NAD gate is given below.
when we se NAND gate to make burglar alarm, we connect one of its input with light dependent resistor (LDR). The L.D.R has resistance that varies with the shining on the L.D.R crease, in total darkness the ODP 12 has a resistance of about 10M and in bright light this falls to a few to a few hundred ohms. variable resistor. The voltage across L.D.R is
In the dark the voltage drop across L.D.R is sufficient to make the input of NAND gate 5V at logic 1. when the light from a burglar’s torch shine onto the L.D.R. the resistance of LDR falls and hence voltage drop across it drops to nearly 0.5V. The gate is now at logic 0 md the buzzer sounds at the output.
Procedure:
1. Make connections according to circuit diagram.
2. Adjust the variable resistor so that voltage drop across LDR is 5v and input b is at 3. 3.Put light on LDR with torch. The resistance of falls and hence the voltage across LDP falls to 0.5v. The input b is now at logic 0. The output is high and buzzer sounds.
Precautions:
1. The connection should be neat and clean.
2. Draw circuit diagram before assembling the components.
3. Use LDR and variable resistor of suitable values.
Viva voce
Q.1: What is NAND gate?
Ans: The NAND gate is combination of and gate followed by not gate.
Q.2: What will be the out of the NAND gate if both inputs are high?
Ans: The output will be low.
Q.3: What will be the output of the NAND gate if both inputs are low?
Ans: The output will be high.
Q.4: Name the gate formed when two inputs of NAND gate are joined together.
Ans: NOT gate
Q.5: Can we convert NAND gate into AND?
Ans: Yes, we can convert NAND gate into AND gate and OR gate. The AND gate is obtained by doing two NAND gates. One of the two NAND gates is as a NOT gate by joining its input terminals.