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
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"
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.
1.25” x 2.6”
provides 3.7V DC
These schematics may be viewed and maniuplated using Eagle.
They are released under this Creative Commons license.