5 Home IoT Devices that would Benefit from e-Paper Displays

E-paper brings several benefits to home IoT systems, enabling them to display information to the user that can be seen in ambient light using minimal power. 

What's more, the technology can display in color (yellow and red), enabling the delivery of eye-catching alerts.

Here we look at five of the best home IoT systems that would benefit from an information display but also need to run for months (ideally years) on just a small battery.

Power constraints of adding a display

Before we get to the applications, it's important to state that the power available to a display will be limited. A typical coin cell, such as Energiser's 2V ER2032 Li/MnO₂ battery, holds 200 to 235mAh, depending on the make. Similarly, a 9V NiMH battery contains around 150 to 200mAh (here's Energiser's again, for comparison).

This prevents the use of a TFT LCD display, which needs to refresh 50 times per second and, for a 2" display, would consume nearly 22,000 mAh of power over the course of a month. This equates to more than the combined capacity of over 90 Energiser coin cells, and would cost in the region of $56 per month).

E-paper displays are bi-stable, which means they don't consume power except when refreshed. And, few (if any) home IoT applications output information that needs to be updated to within a 20th of a second. A similarly sized e-paper display, updated every minute, would consume 65.8mAh over the course of the month. And one where rare updates, e.g. 12 times per day, were needed would draw down just 0.54mAh over the course of the month.

Therefore, it's worth considering the addition of an e-paper display to the following applications, which are ideally suited to e-paper.

1) Smoke alarms

The smoke alarm is arguably the most important system in the house, waking people up and getting them out of the house should the worst happen. But it's also one that is often ignored, with data suggesting that 46% of smoke alarms in the US have dead or disconnected batteries.

This is because a smoke alarm is easy to forget about or ignore. Just a small flashing LED and intermittent beep are typically used to alert the user to the 9V battery beginning to run low. The LED is easy to ignore, and the beep is often very annoying. People often don't have the right size batteries to hand and therefore take the dead batteries out, forgetting to replace them.

By using a bi-stable e-paper screen, a large Spectra black/white/red display could be used to warn people to replace the batteries, with daily screen refreshes to show battery level, consuming less than 0.045mAh per month (0.54mAh per year).

2) Smart energy meters

Smart energy meters are being rolled out across Europe and America, with the aim of reducing a home's electricity use by visualizing usage and helping the user see what appliances are using the most. At their best, they've helped people escape energy poverty by highlighting smarter ways to use renewables.

But at their worst they're ignored, and therefore only add to the energy being used. Consequently, they need to be as efficient as possible and add value - for example using simple colored alerts to warn of high use for the time of day - that helps people make sense of the information.

E-paper displays, which would need to be refreshed no more than once per second, come in a range of sizes ideally suited to smart meters (see our 4.2", 4.37" and 7.4i" displays. All of these size screens display black/white and red or yellow) and are a naturally low-power way to deliver this information using very little energy.

3) Thermostats

Smart thermostats, such as Nest, are playing a significant role in reducing energy bills. They ensure that heating or hot water only comes on when you're home and will need it - not just going on what you tell it you need, but how you act.

However, devices that are intended to minimize energy use should also be designed to be as efficient as possible. The Nest, for example, uses the low-energy wireless standards 802.15.4 and Bluetooth LE to communicate with the boiler/sensors that detect temperature, humidity, proximity, occupancy and light levels) and Wi-Fi to upload data to the internet for analysis/trendspotting, but it also comes with a 2" LCD color display. As mentioned above, replacing this with a bi-stable e-paper display would enable such devices to significantly reduce the energy consumption from the screen.

4) Sports computers

Over the past two decades cycling and running (as well as swimming, hiking and even golf) computers have advanced significantly and enable second-by-second analysis of the ride/run. The biggest user of power on many of these is the TFT LCD display, which is responsible for approximately 75% of all power used.

Switching this to a similarly sized e-paper display refreshed every second would reduce power consumption from the screen by 85%, and allow the computer's 600mAh battery, which is stated to run for 15 hours, to run for up to 38.9 hours - a 160% improvement!

5) Fridge thermometers

E-paper can be used almost universally, be it for weather monitors or humidity trackers, water meters, etc. The temperature range of e-paper can cope with soaring summer temperatures experienced in some countries, functioning normally between 0°C and 50°C. It can also be stored in temperatures as low as -25°C. Indeed, the displays are already used in medical fridges to ensure the temperature is regulated and drugs don't fail.

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