I put together a simple test board for display and wheel. It's called "DUI", not for Developing Under the Influence but for "Development board, User Interface".
Schematics: http://downloads.qi-hardware.com/people/werner/anelok/tmp/dui.pdf Files live here: https://gitorious.org/anelok/anelok/source/dui The board connects via a short cable and UBB to a Ben. The Ben provides power and all control. The board only has the display, the capacitors and resistors required for operating the display, the jog wheel, and a few diodes for multiplexing display and wheel. There is no MCU, RF, or any of the other complicated stuff. This is what the electronics look like: http://downloads.qi-hardware.com/people/werner/anelok/tmp/dui-wheel.jpg The board has the size I'm currently aiming for for the final device. (Note that this is likely to change. I've already grown it by a few mm over the last days, to better accommodate the display.) First impressions of the assembly: - the display's FPC ("Flexible Printed Circuit", colloquially "Flexible Plastic Cable"), while small, was very easy to solder - the data sheet doesn't make it clear, but the contacts are plated on both sides and seem to be connected (didn't test that). This means that one could also run the FPC under the PCB or (in a larger device) run the cable flat, without bending. - that critter is tiny ! It's basically two thin glass plates with a film of magic in between. I was afraid of breaking it, especially when bringing adhesives into the game, but despite its delicate appearance it has resisted all my efforts at destruction so far. - when checking the current setting resistors (R1 and R2, together 760 kOhm), I found that they read far too low. I first suspected that I may have picked the wrong components. But it was probably just the flux. I've seen flux form conductive paths of some 100 kOhms in the past, e.g., keeping chips in reset for a short while (long enough to make the other chip that depends on it fail to come up, yet short enough to destroy all evidence by the time one starts to measure), so this is something to take into account when building this sort of circuit. - the wheel didn't pose any undue problems Then I wrote a little test program on the Ben (using libubb) and brought up the display. The only problem there was that the Ben reset when turning on power on the card slot. This is something that happens quite often when connecting anything but a memory card. I did allow for a generous "charge period" (driving all the data pins high to pre-charge any caps through the pull-ups and only then turn on power), but this wasn't enough in this case. Not sure why the pre-charging trick didn't work this time. The board has only about 11 uF in total and most of that is switched off on reset. Fortunately, turning on uSD power on the Ben with the DUI board present and then hot-inserting it did the trick. The rest of the bringup went smoothly. I made my program display an X bitmap file: http://downloads.qi-hardware.com/people/werner/anelok/tmp/dui-hello.jpg This picture was taken at regular lab hours, i.e., at night. Readability is as good as one could hope for. Today's weather is cloudy and the forecast says it'll stay that way for the next few days. So I won't have a good daylight test for a while. Contrast stays constant at any angle, very e-paperish and unlike LCDs. The display does reflect bright light. I then added Ron's nightmare, some tiny text (5x3 pixels) about 1.1 mm (3.3 pt) in height: http://downloads.qi-hardware.com/people/werner/anelok/tmp/dui-arrow.jpg Even that is barely readable. I then wrote a bit of code that reads the wheel and tries to make sense of its inputs. That code is very primitive (e.g., no debouncing) and it sometimes gets the direction wrong, but it's good enough for demonstrating the concept: http://downloads.qi-hardware.com/people/werner/anelok/tmp/anelok-dui.ogv Xiangfu has uploaded the video to YouTube. I can't get it to load, but this is where it should be: http://www.youtube.com/watch?v=BYlb4---BU8 Don't read too much into what's happening there. That's not a real GUI. All the program knows is how to display a bitmap and to draw a little triangle. It has no concept of characters, fonts, etc. Conclusions: - I like the display. Works without a fuss and performs well. - the wheel also seems to be fine. Debouncing needs some looking into. Since one can't grip the board very well with a Ben dangling off it, it's hard to tell whether the wheel will "feel right", but I'm optimistic about that. - the PCB (0.8 mm) doesn't flex too much, even without a case supporting it. - the wheel may be a bit too close to the display. I'll probably either move the display by a few mm to the left or enlarge the board by a few mm to the right. Depends on how the layout goes. - I initially thought to have a some rigid structure for the spacer between display and PCB but given the flimsy nature of the display, I think just a bit of foam with a weak adhesive (the kind you find on Post-it(r) notes) will do. - the display is susceptible to smudging and scratching. May need a silicone seal when put into a case. Still not tested/checked: - power consumption, - voltage levels, especially the level of the high voltage (the OLED has a DC-DC converter to generate ~12 V), - behaviour when turning on more than 50% of the pixels. This OLED has the known issue of its DC-DC converter being too weak for driving all the pixels at the same time. This shouldn't be a problem for normal white-on-black use, but we'd still want to know what happens when exceeding that limit. - shutdown behaviour. The controller data sheet describes bringing down the rails one by one, but that doesn't seem to be a requirement. Need to check whether anything odd happens if I just do the proper software shutdown, assert reset, then cut all the rails in parallel. I don't expect any issues with that. The next big item will be getting the MCU to work. - Werner _______________________________________________ Qi Hardware Discussion List Mail to list (members only): [email protected] Subscribe or Unsubscribe: http://lists.en.qi-hardware.com/mailman/listinfo/discussion
