Electronic – 7432 behaves like an AND gate & 7408 behaves like an OR gate

circuitsdigital-logicintegrated-circuitlogic-gates

Ok. First of all, I'm an absolute beginner about IC and circuits.
If you will view the pictures, you will notice that the 7432 behaves like an AND gate and the 7408 behaves like an OR gate.
PS. I tried the circuit on a 7487 XOR gate and 7404 NOT gate and it works fine.

So my question is. Is there something wrong with my circuit or is it with the IC?

Switches are on the 1st and 6th on the dip switch. BTW. Disregard the IC on the center of the pictures. That's a 7404 NOT gate. Thanks in advance Sirs.

7432 behaving like an AND gate
1: off —
6: on —
LED: off
7432 behaving like an AND gate
1: on —
6: on —
LED: on
7408 behaving like an OR gate
1: off —
6: on —
LED: on
7408 behaving like an OR gate
1: on —
6: on —
LED: on

Best Answer

It looks like your switches are pulling signals to ground. That means that "on" corresponds to 0 on the input, and "off" corresponds to 1. Similarly, as pointed out previously, if your LED is going from power to the output, when your LED is on the output is low (0) and when off the output is high (1).

If you draw the truth table with all these inversions, you'll find that if both the inputs and the outputs are inverted, your AND(/NAND) becomes an OR(/NOR) and vice versa.

Related Topic