상황
A home automation system uses an ESP8266 GPIO to control a 5V relay through an NPN transistor, with an SPDT switch to manually override the relay state.
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01
Use an NPN transistor (2N2222) as low-side switch for relay coil
02
Include flyback diode across coil to protect transistor
03
SPDT switch selects between MCU GPIO (Auto) and +5V (Manual On)
04
Relay contacts switch an AC lamp with fuse protection
Reusable for any ESP8266/ESP32 relay driver circuit where a manual override or test switch is needed.