E.4 Final SPM Product
A total of 15 SPMs were manufactured using commercial mice electronics and rapid prototyping-based plastic encasings. Although the incorporated PV cell is flat and rigid, curved lines and double-bent surfaces dominate the design. Figure E.4.1 shows the final SPM design together with the support structure to give an impression of the design aesthetics.
E.4.1 SPM Specifications
The 15 SPM prototypes were manufactured in accordance with the different options discussed in Section E.3. A voltage converter (DC/DC voltage up-conversion) charges the battery (of NiMH type of AAA size and 800 mAh capacity) when the PV voltage is above 0.3 V. The voltage converter applies maximum power point tracking by measuring the IV curve of the incorporated c-Si or mc-Si solar cell every 10 s and adopting switching frequency based on pulse width modulation. The voltage converter is incorporated onto the PCB of the additionally incorporated charge controller, which protects the batteries from both deep discharge and overcharge. Should defined voltage thresholds be exceeded, either the solar cell or the mouse PCB is disconnected from the battery. Battery SOC indication already calls for improvement without user tests: A red LED blinks when battery voltage is below a certain voltage threshold. Nothing, however, indicates an (almost) fully ...