상황
A maker builds a Wi-Fi controlled 8-relay board using an ESP8266, driving relay coils through NPN transistors and flyback diodes from an external 5V supply with an LDO for 3.3V logic.
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01
Use NPN transistor drivers to sink relay coil current from 5V
02
Add flyback diodes across relay coils
03
Derive 3.3V logic supply from 5V using LDO
Use for any ESP8266/ESP32 relay controller project with separate logic and relay supplies.