Abstract: An electromagnetic pen with an amplitude-controlled inking function is provided, including a DC voltage source with a high voltage output source and a low voltage output source, a pen tip switch and a programmable LC circuit. The electromagnetic pen outputs an electromagnetic signal. The pen tip switch requires only a small amount of pressure to switch to high voltage output source and trigger the output electromagnetic signal so that the user feel comfortable in writing. The writing and drawing of the electromagnetic pen is controlled by the amplitude of the output electromagnetic signal, which corresponds to the pen tip pressure.

Abstract: The present invention discloses a cordless electromagnetic induction system, which comprises a cordless pen and a tablet, connecting to a host. In this regards, the cordless pen comprises a battery for supplying power to the pen, a RF (radio frequency)oscillator circuit for generating radio frequency signal, representing the location and status of the pen at a central frequency, and a battery voltage detection apparatus for detecting the output voltage of the battery. The battery voltage detection apparatus commands the RF oscillator circuit for generating a signal, which central frequency is at a warning frequency, while the output voltage of the battery is lower than a critical value. The tablet comprises a tablet RF receiver for receiving RF signal from the RF oscillator circuit. The tablet informed the host for raising a low battery power warning to user while the tablet RF receiver received a signal, which central frequency is at the warning frequency.