Switch a 12 V solenoid from a separate supply through a rated driver or relay, with flyback suppression and a fail-state chosen for the mechanism.
Controlling a relay via a web server on ESP32, with a very important safety note on the hazards of working with AC voltage.
Building an SMS-controlled switch for a 12V lamp using a SIM900 shield and a relay, parsing ON, OFF, and STATE commands.
Building a clap-activated switch using a sound sensor and a relay, with simple 25ms timing logic that tells a clap apart from stray noise.
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