This Sunlight-Readable Dual-Display PDA Acts as Its Own Software Development Tool

Pseudonymous maker "jefmer" has taken a compact keyboard kit and turned it into a personal digital assistant (PDA) — adding standalone smarts and a pair of sunlight-readable reflective displays, proving its capabilities by writing the device's software on the device itself.

"I enjoy programming and get frustrated that tablets and laptops are not really usable in direct sunlight," jefmer writes of the inspiration behind the project, which takes as its inspiration pocket-friendly PDAs from the '80s and '90s. "The Pocket Pad prototype is my attempt to produce a small PDA like device that I can use in the great outdoors. To this end, I have combined a PocketType miniature 40% keyboard with two very low power [Sitronix] ST7302 monochrome displays and a Nice!Nano nRF52840 based controller board."

The keyboard is an off-the-shelf kit, designed to put an ortholinear layout in an extremely small space. Normally, a footprint at the bottom-left of the keyboard plays host to an Arduino Pro Micro-compatible microcontroller board that acts as the keyboard's controller — but in the Pocket Pad's case, this has been swapped out for a Nice!Nano with a more powerful Nordic nRF52840.

Above the keyboard, jefmer has added a pair of compact 2.13" 250×122 monochrome Sitronix ST7302 displays. "This display is similar to a Sharp Memory Display in that has no backlight and it permits much faster updates than ePaper displays," the maker explains. "In low power mode with frame refresh set to 4Hz, each display uses on average 30 microamps. It is [also] versatile, in that, in high power mode it can update at a 32Hz frame rate with current consumption still less than 1 milliamp."

The software for the PDA is written in Gordon Williams' Espruino, a JavaScript port built for embedded microcontrollers. While the display and keyboard drivers were developed off-device, along with a text editor, the rest of the gadget's software was developed on the Pocket Pad itself in an impressive feat of bootstrapping.

"The editor can open and edit all of the JavaScript files stored on the device," jefmer explains. "Of course, this means that it is possible to cause a crash that can only be repaired using the WebIDE, however, it also means the device can be used to upgrade itself and fix problems on the fly. The editor uses the arrow keys to navigate and select text, and supports the usual copy, cut and paste operations."

In addition to the editor, jefmer has written a clock application, Bluetooth support for notifications from connected Android or iPhone devices, and an app that allows it to act as a Bluetooth keyboard for other computers. "For a future version," the maker muses, "I cannot decide between a clamshell on the lines of a Psion PDA or a tablet format which would be more robust as hinge-less."

The project is documented in full on jefmer's Hackaday.io page; the source code is available on GitHub under an unspecified license, along with the maker's other Espruino projects.