DIY Smart Water Temperature Controller with Arduino

The DIY Smart Water Temperature Controller uses an Arduino Nano as the central processing unit to monitor and regulate liquid thermal conditions. Temperature data is gathered by a DS18B20 sensor submerged in the water, which communicates precise thermal readings to the microcontroller. The Arduino processes these incoming values and outputs the current temperature onto a 4-digit 7-segment display for real-time visualization. Users can interact with the system via push buttons and a 10k potentiometer to set a desired target temperature threshold. When the water reaches this predefined limit, the Arduino triggers a piezo buzzer to sound an audible alert and activates a 5V SPDT relay through an MCT2E optocoupler circuit. The optocoupler provides electrical isolation between the low-voltage digital control logic and the higher-power switching side, protecting the Arduino Nano from electrical feedback. A 1N4007 flyback diode is included across the relay coil to safely dissipate inductive voltage spikes when the relay turns off. Finally, standard discrete resistors and 5mm status LEDs complete the interface by indicating power states and active heating cycles.