Ivy – A Sensor Network Infrastructure for the College of Engineering

ICM interface

A sensor network, that like ivy, spreads through the environment and links leaves to the root

Jaein Jeong, Lance Doherty and Kris PisterUniversity of California at Berkeley

Electrical Engineering and Computer ScienceLance DohertyJaein Jeong

Project Goals• Research infrastructure of networked sensors

• A lifetime of several months on 1 lithium battery or 2 AA batteries

• Support multiple applications simultaneously

Wireless ICM sensor• ICM (Indoor Climate Monitoring) sensor box

–Measures air speed, ambient / radiant temperature and is made by Professor Ed Arens group.

–Restricted monitoring capability due to the limited memory capacity and lack of constant connection to the host machine.

Sensor calibration• Rationale for Calibration

–Mapping ADC readings to meaningful number.

–ADC variation:Each mote and channel measures the same input voltage with some variance (Fig. 1).

–Non-linearity of temperature – voltage reading: Difficult to fit a voltage reading to the temperature with a single formula (Fig. 2).

• An ICM interface converts

–One anemometer reading(0 – 5V) to voltage input(at most 3.3 V).

–Three thermistor readings (58K to 18KΩ for 10 – 37°C) to voltage inputs.

–For a temperature sensor, two temperature range can be selected (10 – 40°C or18 – 30°C) as a trade-off of long range and accuracy.

• Voltage outputs from ICM interface are fed to a mote as ADC inputs.

Discussion and Future Works• Deployment for environment monitoring

–Plan to set up the 10 – 40 wireless ICM sensors to monitor the campus environment with Professor Ed Arens group.

An ICM sensor box

Thermistor 2(Radiant temp.)

Thermistor 1(Ambient temp.)

Anemometer(air speed)

ICM interface

•Wireless ICM

–We made an ICM interface board to bridge an ICM sensor box and a mica2dot mote.

–Will provide online monitoring and large storage capability.

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10KANEMOMETERR415K

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ICM interface

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INSTRUMENTATIONAMPLIFIER (INA330)

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Thermistor interface

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5 10 15 20 25 30 35 40 45Temperature (°C)

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10 – 40 °C18 – 30 °C

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5 10 15 20 25 30 35 40 45Temperature (°C)

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10 – 40 °C18 – 30 °C

Fig 1. Temperature readingfrom ICM interface

Fig. 2 Variation in ADC reading

• Two stage calibration

–We used two stage calibration:ADC => Vol => Air Speed / Temp.

–Allows using motes / interface interchangeably.

• ADC calibration

–Individually measured for each mote / channel.

–Measured ADC reading for range 0.3 – 3.0V with interval 0.3V (Fig. 3).

–Converts a given ADC reading to voltage by linear interpolation.

• Temperature calibration

–Measured the voltage reading for range 10 – 40 °C with interval 1°C. A temperature chamber was used to set the temperature (Fig. 4).

–Linearly interpolates voltage to temperature.

Thermistor

Fig. 4 Temperature Chamber

Fig. 3 ADC / TemperatureReader Application

–The examples:Building monitoring for critical environmentComfort field study.