Displays

Upgrade your weather monitors by switching to e-paper displays

27th November 2019
Lanna Cooper

The weather has a huge impact on our lives. From simple decisions such as what clothes we wear, to whether our gardens or crops need watering, to deciding if it’s safe to venture out in current conditions, we all need to know what the weather is doing.

By Hardy Kuo, Field Applications Engineer, Pervasive Displays

We get this understanding from a range of sources: our own senses, forecasts and, of course, weather monitoring devices. Often battery-powered, these range from simple units that measure outside temperature, to more sophisticated kit giving a fuller picture of conditions.

And since the arrival of wireless connectivity in our homes and workplaces, increasing numbers of these monitoring stations are linking up to other devices, enabling us to check the sensor data from just about anywhere.

While this connectivity opens up exciting opportunities, there’s still enormous value in having dedicated displays on weather monitors. Rather than having to pull out another device and open an app or web page (which isn’t always practical or safe), a simple glance at a display can tell people precisely what they need to know about weather conditions.

Displays in weather monitors

Weather monitors have long had built-in displays. These are typically Liquid Crystal Displays (LCDs), like the ones found in calculators. These are exceptionally energy-efficient and offer good legibility, but also have limitations.

For example, the display can only show pre-defined shapes, which are set in stone when the panel is manufactured. In the case of a weather monitor, you’ll generally have some numeral areas as well as set text and symbols such as a sun, cloud or low battery indicator.

This severely limits your flexibility when it comes to what you display and how you display it. It also means your device must be designed around the display capabilities of an off-the-shelf LCD panel, or use a custom panel.

These displays are also nearly always two-colour - commonly black segments on a green-grey background. Again, this hampers the richness and impact of the information you can show.

The need for a more flexible display in weather monitors

When exploring ways to make their next generation of products more attractive to consumers and businesses, weather monitor vendors could look at enhanced displays that provide greater flexibility around the information they present.

LCD dot matrix displays are one option, but are typically both single-colour and low-resolution, which hampers your ability to show genuinely rich content. And smartphone-style TFT LCD screens are too power-hungry for devices running on small batteries.

Consequently, for many years, there wasn’t a viable alternative to calculator-style LCDs for battery-powered weather monitors. E-paper, however, is changing that.

The rise of e-paper

E-paper displays (EPDs) shot to prominence in e-book readers. And they’re now becoming the go-to choice for a growing number of applications.

E-paper is incredibly energy-efficient, because it only draws on the battery when updating the display. Once content is there, it remains visible, without requiring further energy. As a result, EPDs can be incorporated into battery-powered weather monitors without excessive impact on the power budget.

EPD energy requirements

To illustrate this, imagine a 2" EPD in a compact weather monitor, configured to refresh every ten minutes between 7am and 10pm.

Each refresh draws 2.33mA, for 2.32 seconds. 90 refreshes per day therefore requires 486.5mAs, or 0.14mAh. That’s about 50mAh per year. A CR2032 battery, which such a device might run on, has a capacity of around 225mAh.

A more sophisticated weather monitor would want a bigger display, such as Pervasive Displays’ 7.4" model. This has 20x the number of pixels to update as the two-inch model, meaning each refresh requires 108.1mAs (46.6mA for 2.32 seconds), which is 2.7mAh per day, or just shy of 1,000 mAh per year. These weather monitors will probably use two or more AA batteries, available in capacities of 2,500+ mAh each.

In both cases, the EPD can comfortably be accommodated in the power budget. And further optimisations, such as only updating the display if the user presses a refresh button, or selective updates to only change certain pixels (a partial refresh), could reduce the energy requirement further.

Other EPD advantages for weather monitors

Add to this EPDs’ ease of readability - even in bright sunlight and at wide angles - high resolutions, and the availability of panels that display black-and-white, as well as black-white-red or black-white-yellow, mean you can present sharp, detailed, eye-catching and easy-to-read information.

And since you have the flexibility to display anything you please, you can use the same panel in different products, or upgrade product capabilities over time with new or alternative views of weather data.

Put together, EPDs therefore provide a compelling package of characteristics that make them an ideal choice for designers of weather monitors, as they look to differentiate their next generation of products.

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