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Relay

A switch the program controls, to turn on and off things with their own power supply: a pump, a lamp, a fan.

The test program

Test this part on its own before you build the rest: if it works alone, the rest is built on something you know works.

10 RELAY on
20 WAIT 1000
30 RELAY off
40 WAIT 1000
50 GOTO 10

What you should see: The relay clicks every second and its LED turns on and off. Try it with nothing connected to its terminals.

▶ Try it in the IDE

What to buy

  • 1-channel 5V relay module (for a pump, fan or low-voltage lamp; never the 230 V mains)The relay just SWITCHES your device. Power the pump/lamp from its OWN supply, never from the board pin. A 1-channel 5V opto-isolated module is plenty.

How to wire it to an ESP32-S3

  1. IN → ESP32-S3: GPIO42
  2. VCC → ESP32-S3: 5V
  3. GND → ESP32-S3: GNDCommon ground: this link is mandatory.
  4. COM · NO → your devicePower the device (pump, fan, lamp) from its own low-voltage supply (batteries or 5-12 V), never the 230 V mains

If it does not work

The board restarts by itself
The load or the relay's coil disturbs the board's power. Power the pump or lamp from its own supply, never from the board, and use an opto-isolated module.
The program runs but nothing happens
The module gets no 5 V, or the signal is on the wrong pin. VCC to 5 V, GND to GND, IN to the pin shown in the diagram.

Which boards it works on

  • ESP32-S3 Freenove: yes
  • Nordic nRF54LM20 DK: yes
  • Arduino UNO R4 WiFi: yes