skill
Transistor switching
A tiny current at the base opens a gate for a much bigger one.
first shows up at Level 3 · Sense
A transistor is an electronic switch — but instead of your finger flipping it, a small electrical signal does. That means a sensor (which can only move tiny amounts of current) can control an LED, a buzzer, or a motor (which need much more).
The three legs of an NPN transistor
- Base (B) — the "control" pin. A tiny current here decides everything.
- Collector (C) — where the big current comes in.
- Emitter (E) — where it leaves, on its way back to −.
The rule
When enough current flows into the base, the transistor "turns on" and a much bigger current can flow from collector to emitter. Roughly:
I_collector ≈ β × I_base (β is often 100 or more)
So 50 µA into the base can control 5 mA through the collector. The transistor amplifies: a small current controls a larger one.
Where you'll see it
Any project where a sensor (LDR, button, microphone) has to trigger something loud, bright, or moving uses a transistor as the middleman. It's the bridge between "I detected something" and "I did something about it".