Today, when I visited my own site, I realized how confusing some of the projects may seem, because they reference different boards and things, and it’s a little bit of a jumble, and it’s hard to tell the players without a program. Figure 1 should sort out some of the details. There are two “homemade” tablets and two “homemade” servers at this point, all ARM CPU architecture powered, by SoC based SBC boards.
Both of the tablets are internal NiMH battery powered, have WiFi, wireless mice, wireless keyboards, and touchscreens. Both have GPIO switches mounted on the enclosure to use for special functionality. Both make use of ADC converters, hooked up to the GPIO for monitoring battery voltage (way better than your store bought, pricey job), they have internal chargers, HiFi audio (hence, the ability to pull in weather faxes when used in conjunction with the SDR sidecar), and a bunch of other features.
The Pi2 based tablet has a barometric pressure sensor (can tell when a hurricane is coming my way), and a GPS unit (so I know how to navigate away from the hurricane). They are both loaded with navigation software of all types, mapping software, and shortwave digital mode decoding software (makes the weather faxes possible). None of this is in your iPad.
I’m currently working on a special RF link, that will couple these little units together without the necessity of using the wasteful WiFi adapters (although those are handy when needed). Internal batteries are good for five hours on both units, and an external pack gives another 5 hours, and is usable with either tablet.
This gets into an area that I’ve structured, so as to increase the interoperability of my stuff. Early on, I was using the boards at their native voltages (i.e., 5VDC, 9VDC, 12VDC, etc). This meant that I had one wall wart power supply for one device, and another (different voltage) power supply for a second device, etc). This was very problematic. It meant that I had to have multiple warts (and warts are ugly). Also, because I liked to use the same style of jack-and-plug arrangement for all my warts, there was the really awful possibility that I’d plug the wrong voltage wart into a device, and make smoke of the health-infringing, crying kind.
So, recently I started a conversion program to make all of my little gadgets harmonious. Now, all of my devices are wall-wart plug’n-play interchangable. Any wart is usable on any device (so long as the amperage ratings are sufficient, and it’s at least 12VDC). This was done by putting input voltage DC-DC converters into everything. Any of the devices can take any voltage, from 12 to 30 VDC, as a result of this decision. Way less crying.
I can power my little tablets with (pretty much) any company’s laptop charger, if it’s at least 12VDC. Likewise, I can charge my internal batteries using a laptop or notebook charger from pretty much any company (if it’s 12VDC or more). Most are.
Don’t you just love the yellow and orange colored server droid boxes? They make me think of lemon drops and orange slice candy, every time I look at them. I do have a sweet-tooth. These are aluminum boxes, from the Hammond company, and they are STOUT. The only caveat I have about aluminum boxes, is that they SHOULD NOT CONTAIN BATTERIES. These boxes are being used by many people for electric vapes, and I’m horrified at that idea. In fact, I think that’s the main consumer demand for these enclosures (could be wrong, but just a quick look on a search engine seems to point that way. DON’T use them for vapes, because vapes use batteries, and Lithium can explode). I’m just waiting for a newspaper headline about that one. It’s just plain silly! This is old news from back in the lead-acid battery days, but people have to re-learn. But they are great for the SoC/SBCs and some associated gadgets.
Another thing I’ve discovered, after working with the myriad parts one needs to build a full-featured homemade tablet: don’t scrimp on connectors. There are various connectors (power, audio, ethernet, usb) that are needed to build a homemade tablet. The cheap ones (10 in a bag for $5) are not worth the postage. It is much preferable to buy some decent ones from a domestic electronics distributor, and save oneself some hair-pulling. 🙂
I’ve discovered some NEW colors in the Hammond collection! People-eater purple, Minty-Blue, and Phosphorescent Lime Green. Well – they don’t elaborate the names of the colors as much as I. But they should. So, don’t be surprised if my mushroom farm of SBCs becomes even more psychedelic.
The pi2 based homemade tablet is 8 x 9 x 1.5, the yellow and orange “candy box” servers are 5.75 x 4.75 x 1.6, and the original homemade Odroid-C1 based tablet is 10 x 7 x 2.5 inches. These dimensions are higher than your average store bought tablet, but then again I don’t work on my projects in the same way as a high volume production plant in Taiwan or China or Japan, either. They design everything onto one highly compacted board layout, one PCB, and wavesolder it.
In my version of things, I purchase many small, independent PCBs and wire them together. The latter approach is much less space efficient, but then again – it’s not store bought all-in-one integrated, and (for the most part) non user serviceable or modifiable. I’ve determined that (at least for my “compact space” soldering and small parts manipulation capabilities) – I need about that much space. To go smaller would require iterative designs to finally mould everything together on a single PCB. At that level, it’s a more serious hobby than what I have going on. I don’t even have a silk screening setup here, and so I buy the boards.
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.
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.
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