Palm Vx Digitizer

A digitizer, also known as "digitiser" is an electronic component, which allows a user to input data in the same way a pen is used. The operation of this device relies on resistive touch-screen technology used in a vast majority of PDA tablets during 2000. This technology enables a user to write on the digitizer layer, which converts the movement of the stylus into digital data and is processed by handwriting recognition algorithms.

Resistive touch screens require a special stylus to write on the digitizer layer. It does not produce any marks and simply creates pressure that the technology detects and captures.

A typical touch-screen consists of a four-wire ribbon cable as shown in the photographs. Each wire usually carries a positional signal, +X, -X, +Y, -Y. These signals are in analogue form and fed to an analogue-to-digital converter (ADC), which converts a pressure value into a digital coordinate. A moving stylus tip causes many pressure points, thus producing a stream of coordinates from the ADC. The main processor then uses this digital data for handwriting recognition algorithms to determine the shape. One of the earliest and well-known software for handwriting recognition was the Graffiti® Software.

Digitizer Layer

Usually a digitizer consists of a pair of layers, which are made of transparent polyester material. One layer has a resistance along the x-axis and is called "x-layer", whilst the other has resistance along the y-axis and is called "y-layer". Both of these layers are stacked to form a grid and usually fitted on top of a glass layer on the LCD assembly.

The borders around the digitizer layers are the electrodes, which are usually made of silver conducting ink. The same ink usually forms the tracks on the ribbon cable, which is why it is silver coloured.

Resistive Touch Screen Operation

When the x value is required, power switches to the x-layer and the y-layer acts as a sensor. When the y value is required, power switches to the y-layer and the x-layer acts as the sensor. Only one reading of either x, or y, is possible at any one time. Hence, in this type of system, the power to both layers alternates very fast, and the ADC usually controls the switching.

Damaged Digitizer - Fix

Usually, a sharp dent to the digitizer layer will short the grid and render it inoperable. When this happens, it will not respond to touch.

Usually, the digitizer layer has glue around the edges, which secures it to a glass layer. An impact to the screen usually breaks the glass. However, an impact does not always damage the digitizer, and occasionally it is reusable. Using a hairdryer to soften the glue around the edges helps to remove the layer.

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