Scrolling electronic whiteboard

1. A scrolling electronic whiteboard, comprising:

a thin-film antenna board, with a thin-film as a substrate, a plurality of wires equally-spaced and arranged on said thin-film to form a two-dimensional matrix of antenna loops;

a scrolling mechanism cassette, for housing said thin-film antenna board, said thin-film antenna board being able to be pulled out from or retracted into said scrolling mechanism cassette;

at least an electromagnetic signal transmitter, with each said electromagnetic signal transmitter having a resonant circuit for transmitting an electromagnetic signal of a specific frequency; and

a main control board, having a signal processing and control circuit and a microprocessor, for receiving antenna loop signals from said thin-film antenna board, and electromagnetic signals from each said electromagnetic signal transmitter;

wherein said main control board enables said electromagnetic signal transmitter, activates a plurality of Y-axis antenna loop in said two-dimensional matrix of antenna loops one by one for receiving a respective antenna loop signal, and a length of said thin-film antenna board being pulled out is determined by the Y-axis antenna loop that has the antenna loop signal with a largest amplitude.

2. The scrolling electronic whiteboard as claimed in claim 1 , wherein said thin-film of said thin-film antenna board is made of plastic material.

3. The scrolling electronic whiteboard as claimed in claim 1 , wherein an area of said thin-film antenna board being pulled out is a drawing area of said electronic whiteboard.

4. The scrolling electronic whiteboard as claimed in claim 1 , wherein an outermost antenna loop of said thin-film antenna board is a confirmation antenna loop.

5. A method for detecting a length of a thin-film antenna board of a scrolling electronic whiteboard being pulled out, said method comprising the steps of:

(a) using a microprocessor of a main control board to issue an enable command to at least an electromagnetic signal transmitter, said electromagnetic signal transmitter transmitting an electromagnetic signal of a specific frequency;

(b) using said microprocessor of said main control board to activate Y-axis antenna loops of said thin-film antenna board one by one, and receiving a signal from the activated Y-axis antenna loop;

(c) determining whether the signals of all of said Y-axis antenna loops have been received, and returning to step (b) if not yet; and

(d) using said main control board to compare amplitudes of the received signals from all said Y-axis antenna loops to find a Y-axis antenna loop of which the received signal has a largest signal amplitude.

6. The method as claimed in claim 5 , wherein said Y-axis antenna loop with the largest signal amplitude determines the length of said thin-film antenna board being pulled out, and a dimensional ratio of said thin-film antenna board being pulled out can be used to adjust a drawing area of said scrolling electronic whiteboard.

7. The method as claimed in claim 5 , wherein said main control board issues a power off command to said electromagnetic signal transmitter to prevent said electromagnetic signal transmitter from interfering with signals from an electromagnetic pen after determining the length of said thin-film antenna board being pulled out.