[lug] hardware question

[Rob Nagler]

Chris Riddoch writes:
> I'm not an electrical engineer - I can say "I think it works by
> induction" without completely knowing what I mean by that, because
> that's what an electrical engineer once said to me. :)

http://en.wikipedia.org/wiki/Graphics_tablet
Passive tablets
    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 stylus. The wires in
    the tablet then change to a receiving mode and read the signal
    generated by the stylus. 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
    stylus itself, not the tablet. On older tablets, changing the
    pressure on the stylus nib or pressing a switch changed the
    properties of the LC circuit, affecting the signal generated by
    the pen, which modern ones often encode into the signal as a
    digital data stream. 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.