Energy Harvesters are starting to be mentioned and talked about by some of the technical e-zines. Basically energy harvesters consist of a circuit to keep a battery or super capacitor charged by collecting small amounts of energy using a transducer. Typically the energy harvester is charging a sensor (i.e. temperature, humidity, light, proximity). Transducers can be photovoltaic cells but since many of the sensors are indoors the solar cell needs to be very sensitive. Another option that might be usable is a piezoelectric sound transducer, which converts vibrations to electricity.
The problem I have with all of the examples I've seen is that they are cost prohibitive for what they are trying to accomplish and to the people who would take them and experiment with them. $35.00 for a semi-working energy harvester and over a hundred for an evaluation kit defeats the purpose of getting the technology out there and working with it.
I am in the process of building a small energy harvester using a piezo-electric transducer to power a wireless temperature sensor. I still have a few more parts to procure and some calculations to work out but, if successful, the time between backup charges of the super capacitor could be significantly extended. The most expensive portion of my project has been the shipping charges because I have been impatient in waiting for the parts. The DC-DC Step-Up Voltage Regulator was a little over five dollars in quantities of one and the rest of the parts are off the shelf capacitors, resistors and some low reverse leakage diodes.
Once I have all the parts, assemble them and test it out I will publish the results (good or bad). Energy harvesters have the potential to allow low current applications to run months, years or effectively forever without the need for battery replacement.
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