Wired expansion for hardware buttons with magnetic plug
The idea was to have a more ergonomic experience while reading off the Nook by using a wire with two buttons on one end and some kind of plug at the other to connect it to the Nook. Since using the USB would mean battery drain and having to run/stop some applications (like the fantastic USB mode by Renate), I tried connecting the hardware buttons directly. Thanks to dkuku and his dead motherboard
I was able to do that. Here's how:
1. Locating the connection points. My Nook motherboard has a label layer with all the test points numbered. The interesting ones are:
T314 - common for all four hardware buttons on the sides
T309 - bottom left button
T310 - top right
T311 - top left
T312 - bottom right
I always hold the Nook in my left hand, so I remapped the right hand side buttons to Menu and Back. Therefore I decided to extend just the two left buttons.
2. The plug. I could not find a proper socket/plug pair small enough to fit into the Nook so I built my own. To avoid mechanical damages I decided to use small neodymium magnets as contacts. You can buy them online. I found some small ones - 2mm in diameter, 1mm thick. To make a plug and socket for two buttons we need 6 of them. To arrange them into identical patterns on the Nook face and in the plug itself I used 3 spent ballpoint cartridges that happened to be exactly 2mm wide inside so that the magnets would fit and the body of an automatic pencil that was just big enough to hold them together:
The spaces between the cartridges were filled with epoxy. Then the sausage was cut into slices - about 2mm thick for the plug and 3mm for the socket. Then the magnets were pushed inside so that they would stick out a fraction of a milimeter.
Magnets cannot be soldered - they will lose their magnetic properties above certain temperature. Conductive glue must be used. I bought a small set for fixing rear window defrosters - a mixture of glue and silver filings. A drop into each tube holding a magnet will do. Then I covered the back of the socket/plug with epoxy to protect the more fragile conductive glue.
I decided to put the socket in the bottom right corner of the Nook frame - partly because I hold it with my left hand so that seemed natural, partly because it would fit in a small air pocket on the reverse side (I had to remove some of the little plastic reinforcing "walls") :
The extension buttons are prototypes - I'm still looking for some that would have the proper feel:
They fit quite nice, although the plug still needs some filing and painting:
The trick was not to put all magnets facing the same poles up so you can only fit the plug one way. Everything works smooth. The lazy reading is best, hands down