A downside to the first tablet, although it does a lot of what I was looking for in my initial application, has to do with the fact that it is a little clunky. It’s over two inches thick, which stretches anybody’s idea of what a tablet should be, and it’s ten inches wide as well. When I decided to downsize the geometry of the next tablet a little bit, to make it an easier thing to carry around, I didn’t want to lose much of the interior space that I’d been using and that was already at a premium. One way to increase the interior space of such a thing is to be more efficient about the layout of the components.
The batteries in the original tablet were housed in standard, square battery holders, which have an overhead depth as well as an overhead width and height. The overhead in the vertical direction was almost a quarter inch, and in the other directions a little more than that. In figure 2 (below) I have laid up a prop for what I might do to get rid of the overhead dimensions. The particular enclosure I selected is only 1.5x8x9 inches – which may not seem like much downsizing – but it’s the last three quarters of an inch that really makes the original tablet a bit uncomfortable in terms of handling. Playing with the candidate new enclosure, I find it is much more comfortable to handle.
Figure 2: A lay-up of a potential battery track to minimize the previous inefficient use of space (multiple square holders).
With the batteries on the end, I save on both sides, and (if I trim the divider) I can use the vertical space for the edge of the TFT LCD display. Some means would be needed to contain the batteries, and a means to easily extract them. I’ve considered that I might use a screw-in plug at the side of the enclosure to allow the “tube” to be easily emptied. some means would then be implemented to keep the batteries in the track snuggly, yet allow for removal.
The inefficiency of the square holders was multiplied in the original design. Since we’ll still need the eight batteries in the new, more compact tablet, both sides of the enclosure may use the track and plug arrangement (for battery containment and removal). It’s still the early going, so I may very well supplant these ideas with others. Stay tuned.
Edit May/2017: Almost two years on, I’ve built three tablets using this form-factor enclosure. They were very inexpensive when I purchased them from Simco Box Co (no affiliation). One particular tablet is so jammed with stuff now, that I am literally unable to find additional space for an additional USB connector to the outside world. It seems whatever space is available, I’ll fill it!
- Tablet #: Hgt Wid Dep Soc/SBC board
- ————- —— —— —— ———————
- Original 7.50 10.5 2.40 Odroid C1
- Tablet 2 8.25 9.00 1.50 Raspberry
- Tablet 3 4.50 5.75 1.75 Raspberry
- Tablet 4 8.25 9.00 1.50 Odroid XU4
- Server 1 4.50 5.75 1.75 Odroid C1+
- Tablet 5 8.25 9.00 1.50 DX-Vortex
In addition to these, I have some unboxed projects, so I have more than an SBC or two lying around here!
The Simco box is the 8.25 x 9.0 x 1.5 box, and it seems to be a good intermediate space enclosure. The 4.5 x 5.75 x 1.75 boxes are too small for anything but the SoC board and maybe one or two small peripherals. On those, I have to mount the LCD display onto the outside of the box. My original 7.5 x 10.25 x 2.40 box could accomodate more stuff, but was clunky to hold. So, I’ve more or less quantified (at least for myself and my purposes) – the sizes I’d use for (whatever) specific purpose(s) I had in mind for the project. The 8.25×9.0x1.5 is my sweet spot, because I like lots of peripherals.
Note: This author and site is not affiliated with the Raspberry Pi in any way. For information about those projects visit http://www.raspberrypi.org “Raspberry Pi” is a trademark of the Raspberry Pi Foundation. The Odroid is a product from hardkernel.com, and is not affiliated with this site. The vortex is a product of DMP and dmp.com.tw and is not affiliated with this site.
Note: the author does not have a recent, applicable background in circuit building, or battery related issues, so this is presented as the work of a hobbyist, and is not meant for duplication by others. Readers should look elsewhere for design advice and info.