AND Logic gate

What it Does

This circuit demonstrates the function of an AND gate. The LED lights up only when both push-button switches are pressed at the same time, showing that both inputs are HIGH.

Components Needed

  1. NPN transistors (BC547) – 2
  2. 1kΩ Resistor – 2
  3. 220Ω Resistor – 1
  4. Push-button switches – 2
  5. Green LED
  6. Breadboard
  7. Jumper wires
  8. Battery (9V) with clip

Step-by-Step Instructions

  • Connect the 9V battery to the breadboard using the battery clip.
  • Create a positive (Vcc) and negative (GND) rail on the breadboard.
  • Insert the first NPN transistor into the breadboard. Label its legs as collector, base, and emitter.
  • Insert the second NPN transistor into the breadboard.
  • Connect the collector of the first transistor to the positive rail using a jumper wire.
  • Connect the collector of the second transistor to the emitter of the first transistor.
  • Place a 220Ω resistor between the second transistor’s collector and the anode (longer leg) of the LED.
  • Connect the cathode (shorter leg) of the LED to the GND rail.
  • Place a 1kΩ resistor between the base of the first transistor and one terminal of the first push-button switch.
  • Connect the other terminal of the first switch to the positive rail.
  • Place another 1kΩ resistor between the base of the second transistor and one terminal of the second push-button switch.
  • Connect the other terminal of the second switch to the positive rail.
  • Connect the emitter of the second transistor directly to the GND rail.
  • Verify all connections, then test the circuit by pressing both switches simultaneously to light up the LED.

How it Works

In this circuit, the transistors act as switches. The LED will light up only when both push-button switches are pressed, which provides current to the bases of both transistors. This allows current to flow from the first transistor’s collector to its emitter, through the second transistor, and then to the LED. If either switch is not pressed, the circuit is incomplete, and the LED remains off. The resistors protect the LED and transistors by limiting the current flow.

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