|Re: Any DIY5 pics out there?|
Message #6 Posted by Eric Smith on 14 Dec 2011, 6:56 p.m.,
in response to message #5 by Walter B
The DIY5 is intended to be available with at least two different keyboard layouts.
One layout will be an -41 style layout, the same as we currently have on the DIY4X, and is not intended for soft keys, although there is nothing in the hardware that would prevent the firmware from offering them. There are only five keys in the top row. The function set of the provided firmware would be similar to the 41CX with some extensions to support the SD card and such. It could support alternate firmware if someone wanted to write some.
The other planned layout is the Pioneer/42s/20b/30b layout, which is intended for soft keys. I believe we can package the DIY5 with this keyboard layout in a package of comparable size to the Pioneer. While it is expected to have a MicroUSB connector (device only, for connection to a PC or Mac), we have not yet decided whether to include a MicroSD card slot. The issue is that SD cards (including Micro) can draw up to 100mA, which is too much for lithium coin cells to reliably provide.[*] We're looking at three possibilities:
This model is intended as a firmware development platform, so the early units would be provided to firmware developers with only a hardware test program in the flash memory. It would be up to the firmware developers to decide what functions they want to implement.
- No MicroSD card, lithium coin cells, slim packaging comparable to Pioneer
- With MicroSD card, two AAA alkaline cells, more wedge-shaped packaging to accomodate the AAAs at the display end
- With MicroSD card, color OLED display[**] instead of B&W, lithium polymer rechargeable battery, slim packaging
If you have a desire for a keyboard layout that doesn't match either the 41 or Pioneer, we'd be interested in trying to accommodate it.
[*] CR2032 coin cells are only intended to provide a peak current drain (pulsed) of about 6.8 mA. When they are fresh, they can do this with only about 0.3V drop. We've found that they actually can supply enough current for an SD card, but at a higher voltage drop. However, near end of life, when you would most desperately need the SD card to work, so as to save the calculator memory to the SD card before the batteries fail, is exactly when it won't work. Near end of life, the internal resistance of the coin cell is very high, so a current spike from the SD card will drive the already low battery voltage below the level that can keep the processor operating. In other words, you'll lose the data in memory that you were trying to write to the SD card.
[**] Oddly enough, the color OLED display is significantly *less* expensive than the black-and-white display. However, it sucks a lot of power, so I don't think it's practical without a rechargeable lithium polymer battery. Personally, I don't want to have to recharge my calculator frequently, so I prefer the black-and-white display and prefer to focus my development efforts on that.
Edited: 14 Dec 2011, 7:03 p.m.