My Homemade Tablet (6: navigator buttons)


Figure 1:  Nice USB connector (compared to pc-board mount jobbers).

The photo (above) shows the super-heavy-duty overkill USB chassis connector, installed. The hole for the connector was cut with a home carpentry toolkit hole saw, of the type made for sawing holes in doors for doorknobs (but about a third of the diameter).  I have since switched to Forstner bits, since I don’t want to shell out hundreds of dollars for Greenlee punches (the professional way to do it).  I wore a mask and goggles, of course, and clamped the workpiece tightly so that it wouldn’t twist. Now I need to saw two more holes, one for the auxilliary USB, and one for the external HDMI.

It’s tricky working with only power tools, and things can get out of alignment pretty quickly. The easy part of the project was putting the SoC board and the LCD display into an enclosure. Just about any SOC board enthusiast has done that. I did it the first day, because I wanted to see something happen. But, making the thing solid and portable, and adding batteries and connectors and buttons for GPIO and whatnot – really adds to the amount of time it takes to build the unit. I hope to have a portable, battery operated experimenter’s kit when I’m done, as well as a “sort-of-kind-of” tablet computer. It’s probably not for everyone.

Edit: I’ve put the following on my (junk filler/uninteresting) list. You may want to skip it:

Revisiting the idea of using momentary contact switches in lieu of a keyboard, I realized how efficient I could make such a system. It’s amazing how much functionality you can put into only three buttons, for navigation purposes. Button#1 would be the app scroller button. Press it and hold it for five seconds to start the app-scroller applet. Once the app-scroller applet appears, touch the button to scroll through the apps, one at a time. Allowing the selector indicator to remain at any position for more than some (arbitrarily chosen) amount of time executes the application. Button#2 is the app-functionality scroller. Pressing it and holding it for five seconds (doesn’t have to be five seconds necessarily) causes the app-functionality scroller applet to appear. Subsequent touches of the app-functionality scroller button steps the desired functionality, until the indicator is left for (an arbitrarily chosen time) period, at which point the functionality is executed. This is the same way that the app-scroller button works. It’s the kind of navigation that might be found in a kiosk environment, although probably not at this level of efficiency.

This kind of navigator takes a little while to get used to, but is second nature and fast afterwards. And – it can be done in the dark. At any time, the app-scroller and the app-function scrollers can be activated by a five second (time period selected, as desired) button press. The system to this point uses only two buttons! A special function selection can assign different purposes to all three buttons (for example, up/down, left/right). The five second “reset” of the main scrollers is always available. All the scrollers are circular, and go round-and-round, which means that a button doesn’t have to be wasted on “enter key” functionality.

While some normal, existing applications might be usable by such a navigation system, by emulating keystrokes, for the most part the navigator requires specially built applications to take advantage of the simplicity. That’s not a problem for me, because most of the applications I’ll be using are custom applications.

Application navigation could also be accomplished by voice recognition. The reliability of such a system in adverse conditions might be a negative factor. Likewise, the touch screen may not be usable in adverse conditions. Even web browsers can be modified to work well with a three button system. A circular scroller has all of the favorite sites on it. Simple, huh?

Next page (wiring harnesses)

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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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