2THE TOUCH-ENABLED LIGHT

LIGHT UP AN LED WHEN YOU TOUCH A TOUCHPAD MADE FROM TWO UNINSULATED WIRES.

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THE CIRCUIT DIAGRAM

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THE PARTS LIST

PART

VALUE

DESCRIPTION

R1

470 Ω

Standard resistor

LED

Red/yellow/green

Standard-output light-emitting diode

Q1

BC547

General-purpose NPN transistor

INTRODUCING THE TRANSISTOR

In this circuit, you’ll use a transistor—specifically, an NPN transistor. It has three pins:

  • Top pin: Collector
  • Middle pin: Base
  • Bottom pin: Emitter

Don’t worry about the meaning of the pin names—just think of them as labels. ...

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