Indoor Micro-Energy Harvesting: complete & working

12Dec07

Testing, comparing and monitoring the feasibility of piezo, stepper and magnetic inductors for indoor energy harvesting.

The whole system works! The energy harvesters are collecting, the xbee radios are sending storage values, Processing is retrieving the data and posting the values to a database, data is being graphed (both web and phone) via php, the Asterisk interface is linking the mobile Flashlite app back to the Processing base, and writing an api a.t. packets from the base station xbee back to a remote xbee.

A chart of the system:

harvestorflowchart.jpg

Link to the real time data logging graph.

The FlashLite app can now graph both voltage data and joule data from the php script and graph both. It functions as a management tool since the xbee’s reference voltage is only 3.3 and thus if a capacitor goes above 3.3 volts the values coming in will be thrown off at 1023, though we have strategically place larger cap’s on each harvester for it to really take a while to reach more than 3 volts. The flashlite app allows me to monitor the voltage in each and if the voltage reaches 3.3 on any device, it gives me the ability to call in and send a message to the base station, which in turn writes a api A.T. command to the xbee on its local serial port to send a message to the appropriate remote harvester xbee to turn a pin high, thereby draining the cap though a tip120 transistor. Its always exciting to have two seemingly unconnected devices/concepts interact and create a seamless system, such a phone call controlling an xbee radio thereby controlling a storage capacitor and an LED or for that matter anything else.

finalimage.jpg

Click here to view a short Quick Time of a power-point presentation of the whole system.

sample code:

Processing data logger code to graph analog values from a capacitor or battery as voltage with a 5volt ref: output as graph + text file + quicktime movie

Processing code to receive xbee api packets, extract the i/o pin data, post it to a mySql database, parse data from the Asterisk server and write an api xbee a.t. command to change pin states on a remote radio.

PHP script to grab values from a mySQL database and graph them online with analog to joule conversion, time stamp, values with mouse over and auto-refresh.

FlashLite app (.fla file) for a cell phone, based on Nokia, to monitor the storage, graphing both the most recent values to the database in joules as well as volts and allows the user to call the asterisk server to connect to the processing base station and drain a capacitor.

Asterisk code still to come – having to make an instruction sheet to load and run java on the asterisk server. In the mean time look up Shiffmans example: processing talking to asterisk.

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