Displays
Information on text-only, monochrome and colour graphical dispays.
End users increasingly expect attractive user interfaces and displays in the devices they use. This poses a problem for hardware developers, though, since users also expect everything to become cheaper, and many graphic displays cost as much or more than all of the other parts in the device. To help give you an overview of some of the displays you may consider, as well as the various costs and resources involved in using them, we've made a simple summary of the three main display types found in most embedded devices today:
Character-Based Displays
The easiest to use and most economical choice, "Text-only" displays are often based on the HD44870 controller and are capable of displaying Latin letters and numbers, and typically some Asian and specialised characters. They come in a variety of sizes and display colours, with 16x2, 20x2 and 20x4 characters being some the most common. They are typically around 5.00 € (for a 16x2 display), and generally only require 7 GPIO pins to operate (4 data pins plus RS, R/W and Enable), making them ideal for cost-sensitive applications or when using low-pin-count MCUs.
Monochrome Graphical Displays
Monochrome graphical displays allow you to control the individual pixels on the screen one by one. They are available in a wide variety of sizes with 128x64 pixels probably being the most common, and are often based on the Samsung KS0108 controller. They have the advantage of allowing added display flexibility (you can use custom fonts and display simple graphical information), but they generally require more GPIO pins to use (at least 11 in most cases), and you will need to create a framebuffer to store the pixel data which will require 1KB of SRAM in the case of a 128x64 pixel display (128x64 @ 1-bit per pixel = 8,192 bits or 1,024 bytes). These displays are generally available in the 15-25 € range, though prices vary depending on size and features.
Full Colour Graphical Displays
16-bit or 24-bit colour graphical displays operate on the same principle as a flat-screen computer monitors, and they offer the greatest flexibility and the most impressive "user-experience". Unfortunately, they also (in most cases) require a dedicated LCD controller and external memory to use, and are thus the most complicated of the three screen types to operate. These displays generally use at least 40 pins, and require a reasonably capable processor to work with, especially in full-colour '24-bit' mode. Prices vary depending on size, but numerous 320x240 24-bit display can be purchased for around 25-35€. Some newer ARM7 MCUs have 24-bit LCD controllers built into them, such as NXP's LPC2470 and 2478, and LCD controllers are common in higher-end ARM9 MCUs.