Published April 2000

LOOKING GOOD

Using a Graphics-Based LCD
Module with C
by Bob Perrin and Tak Auyeung

Start • Software Overview • The Bottom Layer • Initializing the LCD Display • Shadow Display • Drawing Dots and Lines • Printing Text • Extensions • Sources and PDF

Many embedded control applications require a display. Character-based displays are ubiquitous. This is partially because of the low cost of character-based displays and partly a result of their ease of use.

As technology has marched forward, the cost of graphics-based LCDs has brought them into the budget of many embedded applications. However, the ease-of-use factor simply isn’t there for graphics modules.

In this article, we will give you the tools necessary to build a graphics-based LCD into your next project.

THE HARDWARE

When writing for an audience as skilled, yet diverse as the readers of Circuit Cellar, it is always a challenge to pick a hardware platform with which everyone feels comfortable. This is particularly important for this article because the magic is in the software.

We settled on the V25+ Flashlite from JK Microsystems as the supporting hardware. This product was selected for several reasons. First, a previous Considering the Details column covered the basics of using this embedded PC. [1] Second, the software development environment is Borland C/C++ 4.52, which is easy to use and widely accepted. Third, the JK Microsystems, Borland C tools and hardware development kit costs less than $200.

Once an embedded PC was selected, we had to choose a graphics-based LCD module. These devices are available from a large number of manufacturers. Optrex and Densitron are the first two places we usually look for LCD displays. However, after a trip to Wescon last year, we discovered an interesting new form factor for displays, the Chip-On-Glass (COG) module.

COG modules do away with the bulky metal bezel and PCB found in other modules. The controller IC dice is mounted directly to the LCD’s glass substrate. This makes the COG devices much smaller than their older cousins. For a couple of years, LCD manufacturers have offered standard product in COG. Because the cost of the COG modules is the same as the more traditional displays, we settled on the Hantronix HDG12864F-1 128 × 64 pixel COG display.

Of all the COG manufacturers that we spoke with, Hantronix was the most willing to work with us even though we didn’t have a high-volume application. Also, Hantronix publishes its product specifications and application notes on the Internet. Although Hantronix would not supply us with a sample module, they do accept VISA transactions over the phone.

After receiving the display, the next obstacle was connecting it to the JK Microsystems V25+ embedded PC. This task consisted of two parts, electrical and mechanical.

The electrical interface was trivial (see Figure 1). The Hantronix application note "Interfacing to a Hantronix 128 × 64 Chip-On-Glass LCD" was extremely useful. [2] The app-note was written for a Parallax BASIC Stamp II, but the interface described is generic enough to use with any embedded controller.

Figure 1—The HDM12864F-1 is a breeze to hook up to a 7-bit output port.

The worst hardware problem was making the mechanical connection to the 0.020² pitch flex strip that comes off the COG module. The people at Future Electronics helped identify and samples a cable-to-board connector (SFV20R-1-STE1 by FCI Berg) that accepted the fine-pitch flex cable.

FCI Berg makes a similar part, the SFV20R-2-STE1, which is also of interest. The difference between the two connectors is whether the contacts enter the connector facing up or down.

Because we did not spin a circuit board for this project, soldering 30-AWG wire-wrap wire to the fine-pitch FCI Berg connector was a challenging four-hour adventure under a 10× binocular microscope. After the wires were attached to the flex-to-board connector, we plugged the COG module into the connector and wire-wrapped the display to the JK Microsystems embedded PC and the requisite capacitors.

Then, we connected a serial cable between the target system (the V25+ Flashlite) and the development platform (a desktop PC), and hooked up 5 V to the target system.

NEXT

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