Arctic Tank Monitor — low-power nRF9160 LTE-M sensor node for -40°C tank monitoring. Battery powered from a 3.6 V Li-SOCl2 cell, with TMP117 ambient sensing, external I2C ultrasonic sensor interface, nano-SIM, U.FL LTE antenna, and SWD programming.

Compact 2-layer ESP32-S3-MINI-1 piezo TX/RX board for a shared 3 MHz transducer node. Includes USB 5 V input, TP4056 single-cell LiPo charging, TLV75533 3.3 V regulation, ferrite-bead isolated 3V3_ANALOG rail, ~12 V pulsed TX boost rail, low-gate-charge NMOS transmit driver, clamp-protected RX input, 2-stage OPA836 analog receive chain, envelope detector, ADC interface, TMP117 I2C temperature sensor, and status LEDs. Layout intent: piezo centered, RX chain within 10 mm of PIEZO_NODE, boost section remote from RX, digital and analog partitioning, and AGND/DGND star connection near RX front end.

Ultra-Compact 1.8V Energy-Harvested Sensor Node with Apollo4, TMP117, and BQ25570