Saturday Feb 28, 2009

Experiments with a Solar-powered Sun SPOT

Environmental monitoring is proving to be a popular application for Sun SPOTs (see here, here and here). This and other similar applications require a Sun SPOT device to operate for long periods (months) using a combination of renewable energy sources (e.g. a solar panel) and duty cycling -- having the device wake up only occasionally to record and/or transmit sensor readings and sleeping for the most part.

A few months ago, I conducted an experiment that collected sensor readings from a solar-powered SPOT into a mySQL database for almost four weeks. A write-up describing the results is now available as a Sun Labs Technical Report and featured in this week's spotlight on the Labs' home page.

This experiment helped us uncover and fix several issues that caused disruptions in data collection -- the occasional inability of the device to enter deep sleep, the resulting clock reset due to premature battery exhaustion, and loss of connectivity to the database after long periods of inactivity. The report offers important lessons in the design of sensor data collection frameworks and lists both recommended best practices and potential pitfalls to avoid.

As I type this, another Solar-powered SPOT running a new version of our software has been collecting and reporting sensor readings. It has already been up for more than two weeks without any of the disruptions we saw previously leading me to believe that the fixes we incorporated in response to lessons learnt are working well. Watch this space for a follow-on post describing the latest experiment.

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Vipul Gupta

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