Federico Lorenzi florenzi at
Thu May 29 07:37:04 CEST 2008

On Thu, May 29, 2008 at 7:33 AM, Federico Lorenzi <florenzi at> wrote:
> Not really, normal touch screen tablets have a capacitive touch
> screen, which is why they usually only work with a special pen, and
> you can rest your hand on them.
Correcting myself - from Wikipedia:
Passive tablets, most notably those by Wacom, make use of
electromagnetic induction technology, where the horizontal and
vertical wires of the tablet operate as both transmitting and
receiving coils (as opposed to the wires of the RAND Tablet which only
transmit). The tablet generates an electromagnetic signal, which is
received by the LC circuit in the pen. The wires in the tablet then
change to a receiving mode and read the signal generated by the pen.
Modern arrangements also provide pressure sensitivity and one or more
switches (similar to the buttons on a mouse), with the electronics for
this information present in the pen itself, not the tablet. On older
tablets, changing the pressure on the pen nub or pressing a switch
changed the properties of the LC circuit, affecting the signal
generated by the pen, which modern ones often encode a digital data
stream onto the signal. By using electromagnetic signals, the tablet
is able to sense the stylus position without the stylus having to even
touch the surface, and powering the pen with this signal means that
devices used with the tablet never need batteries. Wacom's patents
don't permit their competitors to employ such techniques.


More information about the community mailing list