Problem Statement

Municipal drinking fountains in city parks and public squares frequently sit neglected for weeks when a mechanical tap or valve breaks, wasting thousands of cubic metres of treated drinking water before anyone responds. In addition, early winter frosts freeze standing water inside the pipework, bursting fittings and causing expensive infrastructure damage. Commercial telemetry systems are cost-prohibitive, demand mains grid connections, and run on closed proprietary clouds. This sprout delivers an open hardware retrofit kit that transforms any standard public fountain into an intelligent, autonomous solar node for conservation, leak alerting, and automated maintenance.

Open Hardware Bill of Materials (BOM Hints)

  • Controller & Radio: Espressif ESP32-C3 RISC-V mini module (with deep-sleep power draw of $15\mu\text{A}$) paired with a Semtech SX1262 LoRa transceiver operating on 868 MHz.
  • Power Subsystem: 10W monocrystalline photovoltaic canopy panel; single 3.2V 6000mAh LiFePO4 cylindrical cell (32700 form factor) with TP5000 / CN3791 MPPT-like solar charger and ultra-low quiescent current buck-boost converter (TPS63020).
  • Valving & Contactless Activation: 1/2" brass bistable (latching) solenoid valve requiring only a momentary current pulse (50–100 ms) to open and close, drawing zero quiescent holding current; digital infrared Time-of-Flight (ToF, VL53L0X) or waterproof capacitive sensor for touchless water dispensing.
  • Metering & Sub-Freezing Protection: Food-grade brass Hall-effect flow meter (YF-B1, 1–25 L/min, ~450 pulses/litre); digital waterproof temperature probe (DS18B20) clamped directly to the incoming riser pipe; secondary gravity-drain electromagnetic valve at the lowest plumbing point.

Schematics & Experiment Notes

  1. Pulsed Solenoid Driver: The bistable latching solenoid is driven via a miniature H-bridge (TI DRV8837). To open the valve, a +12V 60 ms pulse is delivered from a boosted reservoir capacitor; to close, an inverted polarity pulse is applied. The total average electronic power draw remains below 0.8 mW.
  2. Anti-Tamper & Leak Mitigation Algorithm: The firmware measures cumulative flow in real time. If the tap flows continuously for longer than 90 seconds (indicating vandalism, a stuck sensor, or an obstructed basin), the valve closes automatically and a high-priority LoRa alert beacon is dispatched.
  3. Automated Winter Freeze Drain: When the DS18B20 probe registers incoming water temperatures dropping below +2°C, the controller locks out the main intake valve and energizes the lowest drain valve to evacuate standing water via gravity, preventing burst pipes without costly heating tapes.
  4. Sanitary & Potable Water Integrity: The system connects strictly to certified municipal drinking water mains. Rainwater harvesting is deliberately separated and diverted purely to sub-surface soil irrigation for nearby trees.
  5. LoRa Telemetry Payload: Every 60 minutes (or immediately on leak/freeze alarm), a compact 12-byte CBOR packet is broadcast: total volume dispensed ($m^3$), current flow rate ($\text{L/min}$), pipe temperature ($^\circ\text{C}$), and battery voltage ($\text{V}$).

Call for Contribution (How to Join)

  • Firmware Developers: Help us optimize the ESPHome / Zephyr RTOS state machine for sub-$10\mu\text{A}$ sleep states and resilient LoRaWAN/Meshtastic reconnects.
  • Mechanical & CAD Designers: We need rugged, vandal-resistant enclosures 3D-printed in UV-stable PETG/ASA or cast aluminium to mount seamlessly onto municipal fountain fixtures.
  • Field Testers: If you are interested in deploying a pilot fountain kit at your local community centre, schoolyard, or mountain hut, get in touch or open an issue on our community tracker.