Relay module 1 channel (5 V) with ESP32

Supply 5 V Bus GPIO

Pins and ESP32 wiring

Pin	Role	ESP32 pin	Notes
IN	Input (the ESP32 drives it)	D25	Many modules switch on with IN LOW. Some do not react to 3.3 V: check with a test
GND	Ground	GND
VCC	Power	VIN	Needs 5 V for the coil: use VIN
COM	Not wired to the ESP32	—	Relay common contact. Mains voltage is dangerous
NO	Not wired to the ESP32	—	Normally open contact
NC	Not wired to the ESP32	—	Normally closed contact

Suggested wiring for the 30-pin ESP32 DevKit, avoiding flash, input-only and strapping pins. BoardPilot checks it for you as you wire.

This module is sold for 5 V. Its outputs may be 5 V: use a level shifter or a voltage divider on ESP32 inputs.

The relay coil needs 5 V: power the module from the 5 V pin, not 3V3. (Songle SRD-05VDC-SL-C datasheet, Coil voltage 5 V)

void setup() { pinMode(25, OUTPUT); }  // IN

void loop() {
  digitalWrite(25, HIGH);
  delay(500);
  digitalWrite(25, LOW);
  delay(500);
}

Part data: CC BY 4.0, free to reuse with credit to BoardPilot.