4: AND Gate with Two Buttons

This circuit is a simple AND gate made with two buttons.

If you want the fuller explanation first, see AND gate in Electricity.

An AND gate is a kind of logic gate. A logic gate is a circuit that turns an output on or off based on one or more inputs.

In this circuit, the two buttons are the inputs. The LED is the output. The LED turns on only when both buttons are pressed, because they are placed in the same path.

Learn more (optional):

Goal

Make the LED turn on only when both buttons are pressed.

Parts you need

Important: choose the right resistor

Your kit has 150Ω and 100Ω resistors.

  • For a red or yellow LED, use 150Ω
  • For a green, blue, or white LED, use 100Ω

Using the wrong resistor can damage an LED.

Build idea

An AND gate only turns the output on when both inputs complete the path at the same time.

This time the buttons go one after another in the same path:

3V3 -> button A -> button B -> resistor -> LED -> GND

If either button is not pressed, the path is still broken, which is exactly how an AND gate behaves.

Build steps

Try each step, then check your work with the blurred photos below. Did you connect it the way you meant to?

  1. Build circuit 2: LED with Button. Build circuit 2: LED with Button.
  2. Unplug the USB, if it's still connected.

  3. Add a second button, making sure it bridges the center of the breadboard. Add a second button, making sure it bridges the center of the breadboard.

  4. Disconnect 3V3 wire from the second button, and connect it to the first button. Disconnect 3V3 wire from the second button, and connect it to the first button.

  5. Using a jumper wire, connect the first button to the second button. Using a jumper wire, connect the first button to the second button.

  6. Make sure the LED is still connected to GND.

  7. Plug in the USB, then test each button one at a time, then both at once. Plug in the USB, then test each button one at a time, then both at once. (button A only) Plug in the USB, then test each button one at a time, then both at once. (button B only) Plug in the USB, then test each button one at a time, then both at once. (both buttons)

The LED should turn on only when both buttons are pressed at the same time.

Schematic Diagram

What to notice

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