LEAD IN: LCD displays are common and come in various types. The LCD Display is a cost effective way to display data or facilitate user interaction.
Can you imagine a cell phone or your brand new cappuccino machine without it’s classy looking LCD display. If you like buttons then hopefully the style is retro, however most of us are attracted to LCD displays; especially when there is a blue or orange back light.
Most commercially available products use custom LCDs, these are specifically manufactured for the product and may include special characters which provide additional information to the user.
The predecessor to the LCD display was the LED (Light Emitting Diode) display. These types of display are effective, to some extent however they are limited in their ability to display different types of information. The LED Display can only display information limited to the number and or type of segments which are available. The LCD display has a distinct advantage as by just simply sending a set of new commands to the display, new content can be presented to the user. For industrial or user to system this is an advantage as a system’s display language for example can be altered to suit the user.
LCD displays are available in almost all shapes and sizes, and the following is terminology which can assist in deciding which one to choose.
- Characters: The number of characters displayed on 1 line. This can be 8, 16 or 20 and depends on the physical length of the display
- Lines: The number of characters of lines the display has either 2 or 4
- Backlight: This feature illuminates the display, and the absence of the feature can result in less expensive unit. Having this feature can ensure that the device remains usable in low light conditions
- Operational voltage: The supply voltage required.
From the basic terminology above, once the character requirement has been decided; most LCD displays have a 4 of 8 bit mode. However, during normal operation most displays can or revert to 4 BIT or nibble mode. The data and command signals for the LCD display are transmitted using this mode. Overall the number of I/O used for the display is less than 1 8 BIT port, which means that in most instance the LCD display can be used on 14 PIN PIC devices with not much of a problem. If you need to go smaller, ie 8 PIN then an I2C LCD display would be the type of LCD display to consider.
If a standard character LCD display is limiting for your application, then the next option would be Graphical of TFT Screen. These types allow the user to program graphics which may be onscreen buttons, analogue displays almost anything the device memory can or will allow. Touch screen displays are more intensive on the PIC, and require the graphics to be mapped in memory which is more complex than the simple placement of character at a line and column position as with a standard LCD.
To view a practical example of an LCD display in use, see the following article: Temperature Display Project