Trackpad pen for use with computer touchpad
View Patent ↗A pen or stylus for use with a finger activated computer touchpad uses capacitively coupled voltage signals to simulate the capacitive effect of a finger on the touchpad. In addition, the pen has buttons that can be utilized to capacitively couple control signals to the touchpad that are interpreted by application software as specific user-defined inputs. The pen has a conductive tip that is placed into contact with the touchpad. By biasing the touchpad electrodes with a properly timed voltage signal, the pen alters the charging time of the electrodes in the touchpad. This alteration in charging time is interpreted by the touchpad as a change in capacitance due to the presence of a user's finger. Thus, the pen can be used with touchpads that were designed to only detect finger movements.
1. An accessory for use with a computer touchpad that uses a periodic AC signal coupled to at least one electrode of a capacitor to detect a change in charging time of the capacitor caused by a user's finger coming into contact with the computer touchpad, said accessory comprising:
an approximately pen shaped housing;
a conductive tip positioned on a tip of the pen shaped housing;
a signal detector coupled to said conductive tip for detecting said periodic AC signal when said conductive tip is placed into contact with said computer touch pad;
a signal generator for generating a negative voltage transition with respect to said detected periodic AC signal that is coupled to said computer touchpad through said conductive tip to increase a charge time of said capacitor in a manner that approximates an increase in charge time of the capacitor that results from the user's finger coming into contact with the computer touchpad.
2. The accessory of claim 1 further comprising a microcontroller for monitoring said signal detector and controlling said signal generator.
3. The accessory of claim 1 wherein said signal generator and said signal detector further comprise at least one transistor.
4. The accessory of claim 1 wherein said accessory further comprises application software residing on a computer coupled to said computer touchpad that interprets predetermined variations in said periodic AC signal produced by said signal generator as control signals for the computer.
5. The accessory of claim 1 wherein a computer monitoring said touchpad contains software that allows the computer to decode predetermined variations in said periodic AC voltage signal caused by said signal generator as data.
6. The accessory of claim 1 wherein said negative voltage transition is a transition between approximately 40 volts to 0 volts in less than approximately 1 μs.