# LOGIC GATES USING SWITCH

We learn logic gates in previous chapter. Now we will see how to design logic gates using switch. Circuit diagrams for logic gates are shown below –

## LOGIC GATES USING SWITCH

### AND GATE USING SWITCH

As we know 2 input AND gate needs, 2 input device, that’s why we are using 2 button (input device). And we need a output device that is LED. We connect button in series for AND Gate.

• So when both button are not pressed it means input logic is “0 and 0”, In that case LED will not glow.
• When any button is not pressed, LED will not glow, it means logic are “0 and 1” or “1 and 0”.
• Only when both button get pressed logic are “1 and 1”, LED will glow see in image below.

So we can say out circuit follows AND gate truth table.

### OR GATE USING SWITCH

Similarly, we know 2 input OR gate needs, 2 input device, that’s why we are using 2 button (input device). And we need a output device that is LED. We connect button in parallel for OR Gate.

• Here, when both button are unpressed it means input logic is “0 and 0”, In that case LED will not glow.
• When any button is pressed, LED will glow, it means logic are “0 and 1” or “1 and 0”.
• And, when both button get pressed logic are “1 and 1”, LED will glow see in image below.

So we can say out circuit follows OR gate truth table.

### NOT GATE USING SWITCH

NOT gate is different from above gate in such a manner, we need only 1 input, that’s why we are using only 1 button (input device). And for output LED is used. We connect button in parallel for NOT Gate. Not gate is also known as logic inverter.

• Here, when you press button it means input logic is “1”, In that case LED will not glow means output is logic “0”.
• And, when don’t press button it means input logic is “0”, In that case LED will glow means output is logic “1”.

Reason resistor connected before button because voltage needs to drop at some resistance to flow current. If we connect resistor after button then as you press button battery is short circuited.

So we can say out circuit follows NOT gate truth table.

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