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proj:gecko:home

Overview

Gecko Version 1 Pictures



Motivation

  • High maintenance cost of battery-powered and wall-powered nodes due to battery recharge/replacement and wall installation/energy
  • Proliferate small (cm3 scale), simple sustainable, hassle-free sensors
  • As sensor size scales down battery volume becomes a bottle neck for long term sensing
  • Current energy-harvesting platform only supplement and recharge battery powered systems
  • Remove battery and embrace environment and event powered sensing
  • Extend existing Sensornet trees that contain wall-powered trunks and battery-powered branches with energy-harvesting leaves

Objectives

  • Show indoor photovoltaic (IPV) powered sensors are feasible with one minute sampling intervals even under poor lighting conditions
  • Create cm3 scale, full featured wireless solar energy-harvesting sensors using existing/older commercial hardware and software
  • Replace battery with photovoltaic energy (solar cells) as the main sensor power source
  • Show the feasibility of sporadically/periodically energetic leaf to periodically active branch (asynchronous) communication

Accomplishments

  • Built a ~6 cm3 solar energy-harvesting sensor platform using EPIC Core platform (Dutta) and commercial solar cells
  • Small button cell battery is only for maintaining state and time via Real-Time Clock (RTC)
  • Optimize existing TinyOS software stack to cold boot, sample ADC, and transmit radio (IEEE 802.15.4) message in less than 4 ms with 149 uJ energy.
  • Branch node can search, find and communicate with leaf node using only 2.4% utilization even when leaf node looses time.

Publications

Future Work

  • Replace RTC backup-battery with Super-Capacitor to maintain time (overnight) and use FRAM to maintain state (indefinitely).
  • Outfit CSE building with full trunk, branch and leaf sensor network and experiment with high density leaf deployment
  • Explore the feasibility of sensors powered only by their monitored event (light, micro-wind HVAC, vibration, etc.).

Resources

Datasheets

To Do

  1. Put gecko code in repo somehow
  2. Build 6 Geckos
  3. Sync with battery powered node

Readings

BQ25504

  • Stats
    • 330 nA quiescent current in under-voltage mode
    • 570 nA quiescent current in over-voltage mode
    • Vin from solar cell (or whatever) range from .13 to 3 V
    • Needs Vin=330 mV to start the boost converter, once started can harvest down to Vin=80 mV.
  • Notes
    • Chip can control Vin to operate near a reference voltage, allowing the power source to work at the maximum power point.
    • Chip can monitor the battery voltage level and compare it to a reference. When the battery voltages gets too low, the chip asserts a pin telling a uC to shed load.
    • Chip will only charge battery when it can provide voltage between to user supplied voltage references.
    • Boots up with very little voltage either in the battery or on Vin, but has to change internally to 1.8 V when the boost regulator will turn on.

MAX17710

  • Stats
    • 1 nA quiescent current draw from battery in off/shutdown mode
    • 450 nA quiescent current with output regulator off, charger below regulation voltage
    • 725 nA quiescent current with output regulator on (can drive 75 mA)
  • Notes
    • Can output 1.8V, 2.3V, or 3.3V using output LDO
    • Can handle high voltage or low voltage harvester inputs
    • Uses internal boost regulator and external circuit to charge the battery from a low voltage source as if it were a high voltage source
    • Turns off regulated output if battery voltage gets too low
    • No MPPT

LTC3108

  • Stats
    • 200 nA quiescent current from Vout
    • 6000 nA quiescent current VAUX
    • 100 nA leakage VSTORE
    • 100 nA leakage Vout2
  • Notes
    • Secondary Vout2 can be enabled by the microprocessor to power sensors/whatnot only when they are needed.

proj/gecko/home.txt · Last modified: 2012/11/26 18:47 (external edit)