Switching to a Color Segment Display
Changing to a color Segment display
A color segment display can be a great way to give your product a new look with minimal cost increase. Although segment LCD displays are an older display technology, they are still very popular in many new product designs. In this article we will cover the ability to add color to a segment LCD Display product with minimal cost and no redesign of hardware or firmware. The end result is a product that stands out from the rest with a color segment display.
This story is of how one manufacturer converted their current monochrome seven-segment display to a three color segment display without increasing power consumption and at a minimum retooling (NRE) cost.
GTT Industries:
Glucose Testing Technologies or GTT (not their real name) builds a portable technology product that monitors blood glucose levels. It is powered by one AA (1.65V) battery and contains a TN (Twisted nematic) segmented LCD module with three 7-segment numbers plus four additional icons.
The LCD glass is built in negative mode and driven at 3.3 V at around 500uA to 750uA.
The glucose monitor also contains one SMT white LED backlight with a current draw of 12mA.
GTT realized that their competition was introducing a color version of their glucose monitor that incorporated a small passive OLED (Organic Light Emitting Diode) display, so GTT’s marketing department decided to redesign their current product and upgrade to a multi-color OLED LCD while limiting the overall cost increase to less than 20%. And of course, marketing wanted prototypes yesterday.
LCD Redesign: Over budget and behind schedule
Engineering began the redesign to incorporate the OLED display that marketing had chosen. Advantages of the new display included:
- 64K colors
- Resolution of 96×96 dots
- SPI or 4bit/8bit interface
But engineering quickly realized that they would not be able to stay under the 20% goal. In fact, they would not even be close to that goal; and lead time would be seven to nine months minimum.
COST OVERRIDE ISSUES INCLUDED:
- Redesign of the entire case for the new OLED display
- An estimated $20,000 tooling cost plus sixteen week lead time
- Redesigning the interface from a 4:1 mux to a SPI or 4bit/8bit bus.
- Not to mention a new u-controller to drive the OLED display
- Rewrite of firmware to switch from a 4 com segment to a graphical/serial interface
- Increased power-drain (12mA for segment to an estimated ~30mA for the OLED) requiring a change in the charge pump and decreasing the life of the current battery.
This was not going to work for the current low cost version that was in production; it might be good for a future project that offered more benefits that the customer was willing to pay for, but their current customers were not willing to pay for a Cadillac when all they needed was a Chevy.
The solution: Silk-screening the segment LCD
Engineering suggested not switching to a new LCD technology, but instead, modifying their current segment display by adding three additional colors; these would be added by the process of silk-screening the pigments onto the glass.
Silk-screening is not a new idea and the process is simple. After the LCD glass is cut the icons and segments are burned on then colors are silk-screened over specific icons/segments.
Color Segment Display Cost Savings:
The one-time tooling cost to modify the LCD was $1,200; which included: prototypes, design of the LCD and US based support.
The unit cost of the display increased by five cents each and was 100% compatible with the current LCD; it could even be used for repairs/upgrades of units currently in the field.
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