ColdTrace: A Low-Cost Cold Storage Performance Tracker with Smartphone Temperature Alerts

Temperature control is the most important requirement in cold storage, since perishable goods such as fruits, vegetables, dairy, meat and fish spoil quickly outside their safe range. Periodic manual thermometer checks cannot catch a temperature rise that begins and grows between two inspections. This paper presents ColdTrace, a low-cost embedded Internet of Things (IoT) node that monitors the temperature inside a storage unit and warns the user when a set limit is exceeded. An ESP32-WROOM-32 microcontroller reads a DS18B20 digital sensor over a single-wire interface and compares each reading with a threshold in software. When the threshold is crossed, the board uses its built-in Wi-Fi to send a “PROBLEM ALERT” to the user’s smartphone through the Blynk server. Because the sensor gives a digital output, no analog-to-digital conversion circuit is needed, which keeps the hardware simple. The design, working principle, circuit connection and alert logic are described. ColdTrace reduces dependence on manual inspection and offers an affordable, easily reproducible monitoring option for small cold storage units