the battery module
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the battery module

Our 2-part battery module is developed as a rechargeable power source for wearables. It is designed for an on-board lithium ion battery with a capacity of 740 mAH, and to be recharged via a USB port.

While many electronic components can withstand a good wash, a battery is not one of them! We experimented with various materials and ways in which we could make the battery removable. We did not want to resort to standard electronics connectors as that would render garments looking more like "devices". We also decided against regular snaps as they did not feel sturdy enough for a power connection, and we also wanted a connection method that was strong and yet really easy to attach and remove.

We were staring at magnet snaps for a few weeks before it dawn on us that the solution was right in front of us the entire time! So after much experimentation we used a 3 -magnet snap attachment (power, ground and data) to a garment-mounted carrier board and designed a mating board with the battery, battery circuit, and charging unit. This also meant that we can re-use the same battery board for multiple garments.

The carrier board has four reconfigurable wire ports, allowing flexibility in the polarity and means by which power is applied to a circuit. The 3-wire connection lets the battery board communicate with, and power elements on a garment.

The power source for the system merits special attention as the design decisions highlight many of the peculiar challenges of designing for wearable computing systems. Principle design goals for the power source were that it should be easily rechargeable, modular, small, light, robust, and that it should provide high energy density. None of these goals are necessarily unique to wearable systems, however the specific needs of wearables tend to re-define what is "small", "light", and "robust" enough.

We based the power module around a lithium ion (LiIon) rechargeable battery pack offering a total storage capacity of 750 mAh. With the USB port emerging as the most ubiquitous standard DC power source, we equipped the board with a miniature USB jack and designed the charging section around the 5V, 500 mA provided for in the USB standard.

Dimensions
1.25” x 2.6”
provides 3.7V DC

Download Schematics
These schematics may be viewed and maniuplated using Eagle.
They are released under this Creative Commons license.



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