I'm planning on a little experiment with a friend. We're gonna be using 2 Xbee series 1 modules at 3.3V and 50mA. One of the Xbee modules will be sealed in a music instrument and I was wondering: is it possible to power it using energy harvesting?
The instrument will be in constant vibration while in use, frequency will be from 80Hz to 350Hz, concerning the amplitude I don't have a clue yet as I'm building it, but it isn't constant for sure as it changes according to the music. The instrument is about the size of a guitare with a slightly different shape,it is made of wood.
The power supply needs to allow a range of action from 5 to 10 meters to allow freedom with the instrument.
The radio can't go to sleep while in use , and needs to reach 250kbps in order to tansmit sound data with a quality near mp3.
What kind of device or electrical circuit could I use to do so? Is it even possible to have 3.3V with energy harvesting ?
Best Answer
I think you'd be hard pressed to get the required 150mW or so, although it isn't impossible.
Looking into piezo-based energy harvesting systems, one product claims about 7mW constant power. I would assume this scales reasonable well though. This is using a 3x7cm bendable piezo element and some electronics to store and convert the energy. There's a lot of info on piezo.com.
Using the device above you'd need 20-25 of these elements. As they flex quite a bit and obviously should not touch each other, you end up needing quite a large box.
If, however, you are able to design the radio so it only transmits at a low duty-cycle and goes into some deep-sleep power saving state if it doesn't transmit, this seems feasible.
Although he isn't using XBees (but RFM12B radios), have a look at the jeelabs.net website - there's some examples on low-power use of microcontroller driven radios.
With the added detail that the frequency of the vibration will be between 80-260Hz, have a look at this device. The specs state it can generate 7mW at 50Hz - they're not cheap though at $600 for a kit. And you'll be needing something in the order of 25 of them.
Two bonus links: Linear has done some research on this (you've probably seen this already), using this sensor. Quote: