AN0101 - Understanding LCD Panel Dimensions for Bezel Design

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Mounting your SIM in an enclosure, designing a bezel, and understanding how to put a gasket between your SIM and bezel to ensure dust or even a water-tight seal can be challenging.

Serious provides a complete Mechanical Design Package, or "MDP", for all new SIMs. The MDP includes 3D STEP files that mechanical designers can import and use directly in their CAD packages as well as a human-readable blueprint-style PDF drawing. In each drawing, depending on the touch technology for the specific SIM (e.g. Resistive, Capacitive, None) there are important dimensions of the various "zones" of the display you need to understand in order to create a bezel and mount the display in your enclosure.

Resistive Touch

When using a SIM with Resistive Touch (LCD Option Codes starting with "R"), you'll find 2D drawings such as found in the SIM231-A01 Mechanical Design Package (MDP):

SIM231 LCD2D.gif

The terms in this diagram are as follows:

Frame Outer (FO)

Frame Outer is the outer frame of the LCD display. Make sure if your bezel hangs down you give at least 2mm clearance outside this dimension.

Touch Panel Outer (TPO)

The Touch Panel Outer dimension is the outer edge of a resistive touch panel's Mylar layers. Any pressure applied with a gasket should not overhang this edge or the outer edge of the plastic will deform and affecting the performance of the touch layers. Typically the outer edge of any gasket will start just inside this dimension.

Bezel Largest Opening (BLO)

The Bezel Largest Opening is the largest dimension of the inner edge of bezel. If you make the bezel any "more open" than this, end users will the see the metal silver-colored conductive traces that are along the edge of the touch panel. The inner edge of your gasket can come to this dimension.

Bezel Largest Opening (BSO)

The Bezel Smallest Opening is the smallest dimension of the inner edge of bezel. Do not make the bezel opening any smaller than this dimension or you may (with tolerance) make it difficult to select icons on the edge of your LCD. The inner edge of your gasket can come to this dimension, but of course no further or your gasket will show outside your bezel.

Touch Panel Sense Area (TPSA)

Touch Panel Sense Area is the area where the touch panel can be pressed. This usually extends a bit outside the LCD pixel area as the touch panels are made to support a wide variety of similar-sized LCD displays. It is important that your bezel gasket (if present) does not anywhere inside the sense area or software readings of the touch panel will be distorted. It is critical that your bezel gasket (if present) does not straddle the edges of the sense srea or permanent damage may occur to the touch panel: ensure the inside edge of your gasket is no smaller than the Bezel Smallest Opening (BSO).

LCD Pixel Area (LCDPA)

The LCD pixel area is the actual area occupied by pixels. You'll want to center the pixel area in your bezel and work backwards from the center of the pixel area to where you mount the SIM. If you take the LCDPA width or height and divide by the number of pixels (800 and 480 respectively) you’ll get the pixel pitch which should match exactly the specs in the technical reference manual (TRM) posted on the web.


Capacitive Touch