|Calunium with 3.3V prototyping power adaptor fitted. Click on the image for an annotated version.|
Why there isn't a 5V regulatorOne of the reasons why I designed Calunium instead of using the Arduino Mega2560 was the inefficient linear power regulators on the Mega2560 prevent low-power battery operation. I considered various high-efficiency low-dropout regulators (the MCP1702 series is a favourite) but decided that as there are so many possible power options (for example, USB, NiMH, alkaline or lithium polymer batteries or solar cell) I would omit the 5V regulator and include a dedicated power connector. I expect that any embedded use of Calunium will require an additional circuit board and that is the best place to locate power supply circuitry appropriate to that particular use.
3.3V or 5V operationOne of the key features I wanted was to allow either 3.3V or 5V operation. By using the auxillary power connector Calunium can easily be powered at 3.3 or 5V. To make protyping easier I've added the appropriate regulators to two small pieces of stripboard, either of which can be placed directly onto the auxillary power connector. Depending on which stripboard is connected the microcontroller operates at either 3.3V or 5V.
|Calunium power adaptors for prototyping; 3.3V (top) and 5V versions. Click on the image for an annotated version.|