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PROMETHEUS Intelligent Multi-Stage Energy Transfer System for Near Perpetual Sensor Networks. A Battery’s Perspective. Medium Depth of Discharge. ENERGY. Shallow Depth of Discharge. DAY. NIGHT. DAY. A Typical Solar Powered Sensor Node. Charging Circuit. Voltage Regulation. vs.
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PROMETHEUSIntelligent Multi-Stage Energy Transfer System for Near Perpetual Sensor Networks
A Battery’s Perspective Medium Depth of Discharge ENERGY Shallow Depth of Discharge DAY NIGHT DAY A Typical Solar Powered Sensor Node Charging Circuit Voltage Regulation
vs Supercapacitor • Medium Capacity • High Leakage • Infinite recharge cycles Rechargeable Battery • High Capacity • Low Leakage • 300-500 recharge cycles Energy Storage Element Designed for Pulsing Applications Is it enough?
AND Intelligent Simple and efficient hardware Complete and powerful control using software Multi-Stage Inefficient and complex hardware? NO!
Environmental Energy • Solar • Characteristics • Sizing considerations • Typically 18mW/cm2 under direct sunlight • Vibration / kinetics • Sound / wave • Heat
Wireless Sensor Node • Duty cycle • Intelligence – self-aware of power levels and able to exert control • Ultra-low power – Telos • Low operating voltage
Secondary Buffer • Li+ vs NiMH • Direct from environment vs from primary buffer • Dedicated charging chip vs software+simple hardware
Sensing ADC Piggy-back Voltage divider trade-off Actuation uC I/O Digital switch Charging Dedicated charging chip? MOS switch vs Digital Switch DC/DC current limiting Control Loop and Chargingby Software
Driver PROMETHEUS DRIVER piggy-backed on application active duty cycle 1. if TempV > 2.2 2. BattV = BattV + 1.45 (TempV − 2.2) 3. if CapV < 2.2 4. SwitchCap = FALSE 5. if CapV > 3.5 6. SwitchCap = TRUE 7. if CapV > 4.4 and BattV < 3.5 8. ChargeBatt = TRUE 9. if CapV < 3.8 10. ChargeBatt = FALSE 11. call Radio.send(STATS)
Conclusion Multi-stage + simple hardware + software == Perpetual operation
Future Work • Deployment of 1500 nodes equipped with Prometheus for long term observation Questions
Energy - Fundamental Limitation of Sensor Networks • How long could current sensor networks survive without human intervention? 2 to 3 years • Why? Limiting factor storage device
Multi-Stage and Intelligent • Environmental energy unpredictable buffer battery recharge cycles • Sensor nodes pulses storage designed for pulsing applications not batteries • Sensor nodes uC brain can adapt All these points to … • Reduce stress on critical path components • Intelligent
Medium Capacity High Leakage Infinite recharge cycles High Capacity Low Leakage 300-500 recharge cycles Primary Buffer vs