Transistor (NPN)

Meet the NPN bipolar transistor, SparkVille’s little gatekeeper. Its three connections are the base (B), collector (C), and emitter (E). In a suitable circuit, a small current from base to emitter controls a larger current from collector to emitter. It can switch a light on and off or amplify a changing signal. The extra energy comes from the power supply — the transistor does not create it!

The emitter arrow points outwards for NPN. To switch from the negative side of a supply, connect the emitter to negative and feed the base through a resistor to turn it on. Bringing the base back to the emitter’s voltage turns it off. Check the part’s pin order and limits: NPN and PNP cannot simply swap places.

At the lantern gate, a sensor sends a small signal through a base resistor. The NPN transistor switches on an LED lantern powered by a battery, with another resistor keeping the LED current safe.