Digitizers

Digitizers, which are also called digitizing tablets, drawing tablets, or just tablets, are drawing tools that capture the movements of the operator's hand. Their operation is similar to that of a mouse, but there are major differences. The input from a mouse is always relative to where the cursor is on the screen. If you draw a line with a mouse and then pick up the mouse and move it to a different position on the desk, the input will continue from the last position of the cursor. However, a digitizing pad relates each position on the tablet to a specific position on the screen. This makes it possible to accurately trace an existing drawing, or to create original drawings, such as an architectural design, which must correspond to precise dimensions.

A digitizer is made up of two main components: an electronic tablet and one of two types of drawing devices. One type is a pen (also called a stylus), which is held like an ordinary pen and used to "draw" directly on the tablet. These movements are captured and translated into a corresponding drawing on the PC. The other type of drawing device is called a puck (or a cursor), which closely resembles a mouse and is used in much the same way. A small window with crosshairs makes the puck ideal for very precise tracing of existing drawings. In both cases, the tablet detects the exact position of the drawing device and sends x and y (left and right and up and down) coordinates to the PC. Pens and pucks are available with and without cords.

Like scanners, digitizers connect to the PC in a variety ways. Most digitizers connect through a proprietary controller card. There is no standardization among the types of cables used between theses proprietary interfaces and the tablet, so the manufacturer must be contacted for replacements should one become necessary. Some digitizers use the serial port, with one end of the connecting cable attaching to the PC with a standard DB 9 or DB 25 connector. However, the other end of the cable, the one connecting to the digitizing tablet, is usually a proprietary connector. There are newer models that now use a USB or IEEE 1394 connectors as well.