Cold-chain temperature logger with excursion alerts

Gulf Fresh delivers medicines that must stay between 2 °C and 8 °C. Each van carries a USB data logger that a driver downloads once a week. Last August a van's compressor failed in 46 °C heat on the way to Al Ain. Nobody knew until the weekly download, and a pharmacy group rejected an insulin consignment worth about AED 140,000. The quality manager now wants a connected logger that warns the dispatcher while there is still time to act.

Her requirements are: - record temperature every minute with an accuracy of ±0.5 °C between 0 °C and 15 °C; - store at least 30 days of readings on the device, so nothing is lost when the van is out of coverage; - alert if temperature stays above 8 °C or below 2 °C for more than 10 consecutive minutes, and alert if the cargo door stays open for more than 3 minutes; - upload readings every 5 minutes when there is a connection, and send alerts immediately; - calculate mean kinetic temperature for each trip, which the pharmacies ask for.

You will write the requirements, choose a sensor and build an error budget, write logging firmware with a ring buffer, write the alert logic as a state machine, publish over MQTT to a broker, and write a small Python consumer that stores readings and calculates mean kinetic temperature. Everything can be built and tested in the Wokwi simulator with an ESP32, a DS18B20 sensor and a push-button for the door switch. If you own an ESP32 and a DS18B20, you can run it on hardware too.

Done looks like firmware and a consumer that run end to end, a test report showing alerts fire at the right time on recorded excursion profiles, and a short note the quality manager can use to decide on a vendor.