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Cold-Chain Telemetry Mesh

Built a low-power ESP32 sensor mesh that monitors vaccine-fridge temperatures across rural clinics, surfacing excursions in real time over intermittent connectivity.

C++ ESP32 ESP-NOW MQTT FreeRTOS Grafana
Source

Problem

Clinics lost vaccine stock to undetected fridge failures. Cellular coverage was patchy, mains power unreliable, and staff had no time to read logs.

Architecture

A battery-backed ESP-NOW mesh lets leaf nodes hop readings to a single gateway, which buffers locally and syncs to MQTT when the network returns.

// Leaf nodes sleep aggressively; wake only to sample and forward.
esp_sleep_enable_timer_wakeup(SAMPLE_INTERVAL_US);
if (temperature > THRESHOLD_C) sendUrgent(reading);   // skip the duty cycle
esp_deep_sleep_start();
  • Resilience: store-and-forward survives multi-hour outages without data loss.
  • Power: deep-sleep duty cycling pushed leaf-node life past 6 months on a coin cell.
  • Alerting: threshold excursions escalate to SMS within seconds of reconnection.

Impact

  • Zero unreported excursions across a 40-clinic pilot over six months.
  • Hardware BOM under $9 per node at small volume.
  • Operators trust a single dashboard instead of a clipboard.