DIY4X, DIY5 update

[Eric Smith]

Last month Angel Martin asked for pictures of the DIY5 (which doesn't exist yet), and I explained that the DIY4X that I showed at the HHC 2011 broke as soon as I got it back to the hotel.

Today Richard Ottosen finished assembling the first of the new DIY4X display adapter boards, and I made the necessary minor changes to the firmware, and we were both amazed that it worked the first time.

There are some photos here. The third photo in particular shows off the display, although not under ideal lighting conditions.

Richard will build two more display adapter boards so that we can upgrade upgrade the other two DIY4 calculators to DIY4X.

The new display adapter board also is designed to provide USB support, once we upgrade the processor to the newer chip with USB support (and more RAM and Flash).

We might make a few more DIY4X calculators for firmware development, but after this the main development thrust will be the DIY5, which will be functionally similar to the DIY4X, but designed for manufacture.

[Massimo Gnerucci (Italy)]

Thank you for the update Eric, really nice beast indeed!

Greetings,
Massimo

[David Griffith]

Do you have any pics of hardware with the alternate keyboard?

[Eric Smith]

We haven't built the alternate keyboard (42S/10b/20b layout) yet. If we build more DIY4X units, we'll build the alternate keyboard and kludge it onto some units. However, the DIY4X with the alternate keyboard will be the same overall length as with the regular (41C) keyboard, because it will still have the full length of the DIY4 main board plus display adapter.

The objective with the DIY5 is to have a separate keyboard, so that the with the alternate keyboard layout, the calculator will be the same width and length as the 42S. The height will not match as the calculator will be more wedge-shaped to accommodate the two AAA cells at the display end.

[Ángel Martin]

It´s looking good, nothing short of the expectations created from the HHC reports. Looking forward to the final product!

[Eric Smith]

Designing the DIY4X such that it can be powered from either 3V (lithium coin cell, or two alkaline AAA cells), or from 5V from USB, while not drawing more current from the battery than we previously had without the USB circuitry, was slightly tricky. We weren't 100% certain that our method would work properly, but we tested it this evening and it seems to work OK.

When powered from USB, we still have about 15uA of drain from the battery, regardless of what mode the calculator is in, off, idle, or running. Part of that is the quiescent power consumption of the boost regulator used to power the calculator from the battery, but that doesn't explain the full 15uA. However, we feel that 15uA is low enough that it is not an issue. That's about the same current that the DIY4X draws from the battery when "off" and with no USB power. (We expect to do several things to reduce the "off" current in the future, but aren't sure how it will affect the battery drain when USB power is applied.)

The USB port will not recharge any kind of batteries, and supports calculator operation as a USB device only, not host or OTG.

We don't yet have the new processor with USB support (and bigger memory), so at the moment the actual USB data lines are not wired.

The MicroSD socket will eventually be jumpered over to the SD socket footprint on the DIY4 main board.

Here are three more sets of photos:

• original DIY4 with 16x2 character LCD module, as built in July 2011
  
• DIY4X display adapater (not attached to main board)
  
• DIY4X powered from USB port
  

I'm sorry that the pictures aren't better; I don't have a real digital camera or tripod here, and have been forced to rely on my cell phone.