Design secure remote ESP32 control with HTTPS or MQTT, authentication, authorisation, replay protection, audit logs, and fail-safe outputs.
A look at the DS1307's details: its backup battery system, the SQW square-wave output, and its built-in EEPROM memory.
Using a single-channel relay to control a high-voltage device from one Arduino pin, with a very important safety note on high-voltage hazards.
Wiring a Nokia 5110 display via the SPI protocol to Arduino, with a technical note on signal voltage protection resistors.