XOR gate using op amplifier (AOP), LM324
Électronique / Electronic

In this project, you are going to make an exclusive OR circuit using an OP amplifiers. Do you know the logic of exclusive OR?

In exclusive OR, when two input states match, logical 0 is given. In this circuit, when keys S1 and S2 match in their ON/OFF state, LED 1 goes out. When the keys do not match, LED 1 lights up.

After you finish wiring, turn power ON, and then toggle the keys S1 and S2 between ON and OFF in different combinations.

Check that the lighting status of LED 1 changes as shown in the table.

The OP amplifier serves as a comparator. Let's review how a comparator works. When input voltage at the"+" terminal is higher than that at the"-" terminal, the output of the amplifier is High.

If both S1 and S2 are OFF, the output of U1A is Low (approx. 0 V) and the output of U1B is High (approx. 4.5 V), so that the output of U1C is Low (approx. 0 V) and therefore LED 1 goes out.

Conversely, if both S1 and S2 are ON, the output of U1A is High and the output of U1B is Low, so the output of U1C again is Low, causing LED 1 to go out. On the other hand, if only S1 or S2 is ON, the outputs of U1A and U1B are both Low, and the output of U1C now is High (approx. 4.5 V), so LED 1 lights up.