Touch screens are becoming nearly ubiquitous. Until recently they were only really used for PDAs and POS terminals. Now it isnt uncommon to see touch screens on high end appliances and electronics. It makes sense to use touch screen interfaces for a couple of reasons.

#1 It is intuitive for the user. It doesn’t get any simpler than a button that says “Touch me”. Of course, this requires software designed specifically for touch input. The ability to directly interact with the display is a relatively new interaction paradigm that is changing the way applications are designed. Understanding the process flow or experience is necessary in order to create powerful yet usable applications.

#2 Real estate is expensive. Not every device can have a keyboard and mouse input. And even devices that traditionally were simple now require more complex methods of input. It can be quite cumbersome to build interfaces with a button for every function. And even then its expensive to iterate or modify a physical interface because it requires new engineering designs, tooling, purchase quantities, etc. Whereas every touch screen is a dynamic canvas upon which any interface can be applied.

But what does it actually take to implement a touch screen display? I am about to find out. One of the projects I am currently working on is to implement a touch screen display into a high-end digital video switch. It will be the primary input device for configuring and controlling the switch.

I will try to document progress through out the entire project.

Getting Started

We decided to go with a uLCD-32032-P1T(SGC) from 4D Systems. It is a 3.2″ LCD display with resistive touch screen overlay fully loaded with controller.

• 240 x 320 QVGA resolution, 65K true to life colours, TFT screen.
• Display Viewing Area: 48.6 x 64.8mm
• Integrated 4-Wire resistive Touch Panel.
• Easy 5 pin interface to any host device: VCC, TX, RX, GND, RESET.
• Asynchronous hardware serial port, TTL interface, with 300 baud  to 256K baud.
• Powered by the 4D-Labs PICASO-SGC processor
• On-board micro-SD memory card adaptor for multimedia storage and data logging purposes. HC card support is also available for cards 4Gb and larger.
• DOS compatible file access (FAT16 format) as well as low level access to card memory.
• Dedicated PWM Audio pin supports FAT16 audio WAV files and complex sound generation.
• On-board audio amplifier with a tiny 8 Ohms speaker for sound generation and WAV file playback.
• 16 x General Purpose I/O pins. Upper 8 bits can be used as an I/O Bus for fast 8-bit parallel data transfers.

The controller has a 5 pin interface but you cannot connect direct serially. That requires an additional circuit which I will explain later. For development purposes its better to just get the USB-MB5 USB to Serial UART bridge that 4D Systems recommends. It connects directly to the 5 pin header and gives you a mini-USB connection. The drivers will create a virtual COM port which is used for serial connection to upload firmware and compiled code.