From a clothing designer point of view, the focus is on style and aesthetics. From an electronic engineer point of view, the power efficient circuit design is one of the keys between being a master or mediocre in this profession.
Designing electrical function with high power efficiency in mind minimizes the need of power, allowing to use smaller batteries or to have longer working time for the electronic.
The highly informative Computational Textiles as Materials for Creativity Weblog featured last Sunday the power topic for the LilyPad. It gives a rule of thump guide on how to estimate the battery size when using the LilyPad board in eTextile projects.
It’s a very first average estimate and the actual power requirements will depend on how much/long the LilyPad will be running during the use of the application you design. If the LilyPad has to be active, is running a program all the time, the power consumption will be higher.
To make a more accurate power consumption calculation I strongly suggest to read the ‘important note about the power supply’ on Leah Buechley‘s ‘Turn signal biking jacket‘ DIY instructions.
Leah explains very nicely how the selection of conductive yarn and the distance between the LilyPad and the battery in your eTextile project can influence the power needs.