How does my graphire pen and mouse tablet work?

[istara]

The pen is really ingenious - it works like a mouse cursor the normal way, has a double button on the side so you can programme two different functions in, and if you turn it upside down using Photoshop it automatically becomes the eraser tool.

But how does the tablet recognise the pen’s different signals?

What are those signals, magnets? How can there be four different types?

Does it have a battery that I will need to replace? (Neither pen or mouse appears to have an openable section to replace batteries).

Anyone know the ingenious technology behind this - and other - graphics tablet systems?

[yabob]

No batteries. Description towards the bottom:

http://www.dansdata.com/graphire.htm

RF transmission from the tablet provides the small amount of juice needed to power the mouse circuitry.

[istara]

Oh how cool! Thank you yabob. For anyone else dropping by, here’s an extract:

**The tablet sends the pen or mouse a power pulse and then switches to receive mode, going through this cycle about once every 20 microseconds. Which corresponds neatly to the roughly 50 samples per second the tablet delivers.

The power pulse is enough to charge a tiny capacitor in the pen or mouse, and run the on-board digital-to-analogue signal hardware, which takes pressure and/or button data and an ID code (so the tablet can tell whether it’s hearing from the pen or the mouse)**