#37Q4) Electricity and Electronics

Experimental investigation of the truth tables of simple fundamental logic gates and hence identification of the given gates

DifficultyEasy
Est. Time45 mins

Required Apparatus

  • A +5 V direct current supply, * IC types 7432, 7408, 7404, 7400, 7402, 7486, * Light emitting diodes (LED), * 330 Ω330~\Omega resistors, * 1 kΩ1~k\Omega resistors, * A digital multimeter, * A circuit board (bread board)

Scientific Theory

Truth tables of the relevant logic gates are given below. Note that '1' represents high voltage (+5 V) and '0' represents low voltage (0 V).

Image

Image

Experimental Method

  1. Fix a 7432 integrated circuit to the circuit board.
  2. Setup the given basic electronic circuit by connecting 1 kΩ1~k\Omega resistors to pins 1 and 2 of the circuit to act as inputs and a 330 Ω330~\Omega resistor and a LED to pin 3 of the circuit as shown in Figure 37.1. <image>
  3. By connecting the input terminals 1 and 2 to +5 V (1) and 0 V (0) alternately, observe whether the LED illuminates (1) or not (0) in accordance with the truth table of the OR gate.
  4. Verify the truth table of the first gate (out of the four) of the integrated circuit. Measure the voltage across the LED using a multimeter. Disconnect the +5 V supply and remove the integrated circuit from the circuit board.
  5. Connect another integrated circuit and repeat in the same manner followed by all other integrated circuits. Enter the result separately in the truth tables for the six ICs.

Important Points

1
  • Using the truth table obtained, according to the integrated circuit number, conclude the logic gate in each circuit.
2
  • Every integrated circuit here includes four equal gates. Only the first gate has been used above. (It is more suitable to keep the input terminals of remaining gates earthed.)
3
  • Since TTL IC is used here +5 V supply is compulsory. If CMOS IC is used any voltage supply from +3 V to +15 V can be used. Then the values of the control resistors have to be altered. Calculate considering the specifications of LED's as 2.0 V, 10 mA.
4
  • Instead of the above IC's the CMOS IC's 4001, 4011, 4071, 4081, 4069, and 4077 can be used in the respective order.