Abstract: A secure digitizer control circuit and method which drives the digitizer with a random series of excitation signals. The control circuit includes a digitizer and a plurality of drivers for driving the digitizer. A controller varies the excitation signal and calculates stylus position. A stylus detects the potential at a point on the digitizer. Processing circuitry, including an analog front end and an analog-to-digital (A/D) converter, rectifies and filters the stylus signal and applies it to the A/D converter. An input/output link provides an interface between the control circuit and a host computer, such as a point-of-service terminal. A memory stores a lookup table of drive pattern sets and corresponding position equations. In a first embodiment, the controller repeatedly chooses a random sequence of patterns and applies the sequence until the controller senses liftoff of the sensing means from the digitizer. In a second embodiment, controller means repeatedly chooses and applies a sequence of patterns.

Abstract: A method for reducing errors in electrographic digitizer systems where the horizontal and vertical coordinates are quantized at various time intervals. The method minimizes the time skew generated during quantizations and doubles the quantized coordinate pair output rate by utilizing a time-weighted linear interpolation.

Abstract: An automatic fault detection apparatus which requires no human intervention. The apparatus includes a source for energizing the digitizer including a constant direct current source and a constant direct voltage source, and a switch for selectively coupling either the constant current source or the constant voltage source to the digitizer. An analog-to-digital converter couples to the digitizer and to the source. A controller couples to the output of the analog-to-digital converter. Switches selectively connect the source and the analog-to-digital converter to the digitizer and include analog switches controlled by the controller. A non-volatile memory couples to the controller. An indicator coupled to the controller provides information about digitizer operability. A plurality of test electrodes within the digitizer couple to the analog-to-digital converter. Finally, a wiring harness connects the analog-to-digital converter and the source to the digitizer.

Abstract: A method of capturing the coordinates of a handwritten signature and compressing the coordinate data so obtained. The signature is captured in real time by a device such as a stylus-operated digitizer. Compression is performed by examining the location of the signature points relative to a series of guide lines extending in the strokewise direction. The data is stored in compressed form for use in subsequent transactions requiring authorization by the signature which has been so captured.

Abstract: A self-tuning digitizer control circuit and method which employs a tunable excitation source instead of a tunable front end. In addition, the digitizer control circuit includes a stylus for sensing the excitation signal, and a circuit for processing the information signal from the stylus, including a narrow bandpass filter for passing the frequency of the excitation signal and minimizing the passage of extraneous noise. A controller determines the location of the stylus on the active surface of the digitizer and control operation of the circuit. The excitation source includes, in the preferred embodiment, a tunable divide-by-n circuit employing an 8-bit latch, an 8-bit counter, and a state machine. A nonvolatile memory stores the most recent value for the divisor value n. Provision is also made for a tuning method for the divide-by-n circuit.

Abstract: A digitizer screen and method of making. A coated conductive plastic film is perforated and is used in conjunction with a glass or other panel to provide a screen which may be used in an electronic digitizer for converting the position and movement of a stylus or other device on the screen to electrical signals representative of such positioning and movement. The perforated coated conductive plastic film may be laminated to the glass panel to form an integrated structure which does not require the use of masking and etching or similar processes to produce a desired apertured matrix pattern in the plastic film. Various arrangements of the plastic film are disclosed which facilitate the connection of the apertured portion of the plastic film to associated electronic components.

Abstract: A method of producing an image drive signal which is free of skew. Disclosure is made of a point of sale merchandising system having a transparent digitizer mounted on an LCD module. A stylus is used to draw a signature on the digitizer, and the signature is displayed on the LCD module in registration with the moving stylus. Skew effects are eliminated by performing a mapping transformation using a set of 6 transformation constants. These constants are derived from data obtained while placing the stylus over three reference spots on the display.