Monochrome LCDs offer power, cost advantages over color TFT counterparts: Page 2 of 3

May 18, 2017 //By Paul Hooper
Monochrome LCDs offer power, cost advantages over color TFT counterparts
Thinking creatively about the needs of the user interface can help meet challenging power and cost targets when designing products for use in environments ranging from homes or offices to cars or factories.

Simplify system design
Today’s STN LCDs can also help save power consumption and bill of materials costs throughout the system as a whole. Whereas a TFT-LCD usually requires extremely bright backlighting to give punchy colours, the performance of monochrome displays is much less dependent on backlight brightness.

In addition, because there are usually fewer pixels to address, the demands on the display controller or system processor are also lower: whereas the resolution of a TFT-LCD can be 320x240 up to full HD, and with red, green and blue (RGB) channels, a good user experience can be achieved with a monochrome display having as few as 128x64 pixels depending on the application and size. This can ease controller selection, allowing selection of a lower-cost, lower-power device.

Operating at lower clock speeds reduces power consumption and any thermal challenges. Also, less RAM is required to manage the display thereby helping save cost and reduce board size. The exact reduction in RAM demand or CPU loading that can be achieved by such a switch depends, of course, on the application, the size and type of display, and the controller.

Fig. 2: A monochrome display uses low power,
suitable for metering applications.

It is worth noting that a low-resolution colour TFT-LCD may be a viable option for some projects, which can help reduce the number of pixels that need to be addressed and hence allow a lower-cost microcontroller or CPU. This could be implemented as a custom display, or by modifying a standard TFT-LCD. Various other enhancements are possible, such as re-optimising the backlight.

Customise cost-effectively
With careful design of the user interface and system electronics, a monochrome LCD can help product developers meet tight power and cost targets. Moreover, economic factors allow a custom STN-LCD to be developed at a competitive price, compared to a standard TFT-LCD panel.

This gives product designers even more flexibility to specify exactly the right display size, special icons, dot arrays or characters. Fine-tuning of the materials and assembly processes can help optimise environmental performance.

Moreover, long-term availability can be assured. With the right kind of project management, a custom display can be manufactured in the Far East at favourable cost. However, the team in charge needs the skills and experience to ensure that the display received from the factory will meet the specification and satisfy all requirements of the application.

Anders has helped many product design teams achieve an efficient and cost-effective user interface, in a wide variety of projects such as domestic appliances, coffee makers, security entry panels, and industrial controls.

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