Build a simple alert system using a distance sensor, graduated-color LEDs, and a buzzer to detect when someone approaches a defined area.
Build a simple web server on an ESP8266 module to show a temperature reading on a local web page, with a technical note on voltage compatibility between Arduino and the module.
Two ways to measure voltage with Arduino: direct measurement up to 5V, and a voltage divider for higher voltages, with the full calculation formulas.
A practical guide to wiring the MQ-2 gas sensor to Arduino for detecting flammable gases and smoke, with a safety note about the sensor heating up during operation.