How to control GPIO pins and operate relays with the Raspberry Pi | Opensource.com
Control electronics using a relay | The Raspberry Pi Guide
Wiring a 4 channel relay - is this possible? - Raspberry Pi Stack Exchange
Toggling lights with DockerPi 4 Channel Relay - NotEnoughTech
Amazon.com: GeeekPi Raspberry Pi Expansion Board 4 Channel Relay Board Module Power Relay Module for Raspberry Pi 4B & Raspberry Pi 3 Model B+ & Raspberry Pi 3/2 Model B (No Programming
4 Channel Relay Hat Board For Raspberry Pi 4b / 3b+ (plus) / 3b / 2b - Demo Board Accessories - AliExpress
Using the Raspberry Pi to control AC electric power | TechNotes