FIGURE 4. Design of prototype version 1.
each of the components, were likewise mechanically built into the design of the dice.
This prototype demonstrated the feasibility of the concept as well as the availability of components sufficiently small to allow for the desired operation within the target volume. The first version prototype also revealed shortcomings that would be addressed in future iterations of the design: (1) the use of disposable, replaceable batteries was seen as an undesirable complication. These would be later replaced with recharge- able batteries to avoid requiring a structure that could be opened repeatedly. (2) The use of individual LED control was also deemed unnecessary. Instead, LEDs for each side could be grouped together for simplicity, allowing for the reduction of I/O ports used on the microcontroller and providing smaller overall dimensions of the largest chip component.
2) VERSION 2: LITHIUM POLYMER BATTERY WITH A WIRELESS CHARGING SYSTEM
The second prototype improved on the shortcomings observed on the first iteration and is shown in Fig. 5. In this version, the LEDs were not individually controlled by a cor- responding micro-controller I/O port; instead, there were up to two groups per face that would flash separately. This modi- fication allowed for a physically smaller microcontroller with a smaller pin count. The disposable batteries were replaced by a lithium polymer cell; meaning that the case could be sealed upon assembly for additional structural robustness.
However, the modification also necessitated a safety and a charging circuit inside the device and a special methodology to be developed to charge the batteries. An induction charge system was developed to allow non-contact charging.
Finally, ease of manufacturability due to conductive trace spacing was also improved by switching to an overall dice dimension of 19mm per side. Simultaneously, the over- all volume increase allowed for a physical design change, the introduction of significant rounding of the dice corners