The scenario
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.
What is in this drawing
Read the decisions behind it.
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.
More like this