ppk_usb_lufa
Palm Portable Keyboard USB conversion
inspired by this great project ([featured on Hackaday.com](featured on HackADay)
with the main goals/changes:
- keep electronics inside the fold-up case
- make it possible to use multimedia and other key-codes
the later was achieved by porting the arduino code to plain avr-c with lufa for the HID-keyboard handling and half a software serial implementation based on application note avr309 (with code snippets from here)
parts list
- Pololu A-Star Micro (https://www.pololu.com/product/3101) (a similar sized clone will probably do as well)
- 10k ohm 1/4W resistor
- slim tactile switch as the reset button (http://www.adafruit.com/products/1489)
- micro-usb breakout (http://www.adafruit.com/products/1833)
- wiring-pencil and wire
- 3D printed parts to replace the palm-dock
dis-assembly
- remove the metal backplate on the left side (side with the palm-docking port) - take care not to cut yourself on the sharp edges
- remove the two screws connecting the fold-up stand to the keyboard followed by the two holding the docking-port
- free the flexible flat cable from the plastik parts (might need to cut some plastik away)
- desolder the spring-pins from the flat-cable
- to be able to fit the Micro into the tight space its micro-usb plug needs to be desoldered (... fun)
wiring
since these keyboards where built for multiple kinds of PDAs the dock-adapters had to be easily exchangable - that seems to be the reason why the flat cable running from the dock itself is joined to another "commmon" 6-wire flex cable with a special conductive tape that runs the remaining length around a bend to the keyboards pcb on the other side
this common flex cable has the following pinout viewed from above - "through" the keyboard; from left to right:
| Number | Name |
|---|---|
| F1 | VCC |
| F2 | RX_PIN |
| F3 | RTS_PIN |
| F4 | probably TX_PIN, unused anyway |
| F5 | PIN_DCD |
| F6 | GND |
On the Micro the following pins are used:
| flex cable | name | Micro Pin |
|---|---|---|
| - | - | (reset to GND via the tactile switch) |
| F1 | VCC | Pin 5 |
| F6 | GND | Pin 6 |
| F2 | RX | Pin 3 |
| F3 | RTS | Pin 2 |
| F5 | DCD | Pin 4 |
| - | - | pulldown resistor from Pin 8 to Pin 3 |
assembly
- wire the usb-breakout to the Micro (in the final assembly the former usb port faces the micro-usb breakout)
- wire the Micro to the flex cable where the spring-pins of the docking connector used to be
- on the Micro board Gnd and Reset pins are spaced so that the reset button fits perfectly in between (covering +3V and +5V pins which need to be insulated!) putting the button on the board so that it sits flush
- remove the support of the usb-port in the 3d printed part and slightly drill out the screw holes with a 3mm drill, so that the screw heads are flush with the surface
- fixing the Micro and the usb-breakout with some hot-melt glue to the 3d-printed part
- slide in the back-cover (might need to apply some heat to bend it a litte over the electronics, should close up flush with the other 3d printed part)
code compilation
requires gcc-avr and avrdude to compile via the makefile