The above image shows Floyd with the back cover and the battery cover removed. The yellow feature is the display bed, it does tripple duty. It holds and positions the display, it centers the buttons and it works as a light guide for the indicator lights. The right side of the PCB is the high-current area. The external power input and the battery charger sits in the lower part of this area.
The lower end of the case holds the batteries. These are currently 4 LiPoly, 18650 size cells in a 2s2p configuration. The 18650 cells have some great advantages:
- They can be had in fairly high capacity
- They are available in a variety of chemistries
- They are fairly inexpensive, even matched and packaged cells
- They weigh next to nothing
- High discharge versions are available
- Multiple sources worldwide
A major disadvantage is that these cells are cylindrical, so they waste a lot of room.
The image above shows a cut through the unit revealing the back. The batteries are pretty large. A prismatic (flat) LiPoly battery of the same capacity could be made almost half as thick, but the cost would be a lot higher. Why not use AA batteries? AA batteries would deliver less power for the same size and weight. So the battery life would be shorter. Or we would have to fit, say, 12 AA batteries making the unit bulkier and quite a bit heavier.
The above cut shows a bit of the front and this view gives you a sense of how much room the electronics require. We can easily make the rest of the unit 15mm thick (5/8 in) or even less. The cylindrical batteries doubles the thickness. We have put them at the base to keep them a cool as possible, and to keep the unit thin. Attaching them to the back would make the unit lower and more stubby.
Nothing is final regarding the batteries and I don’t think we have found the right power solution just yet. Any thoughts? Hit the comments…