I’m designing an In-Home Display (IHD) which will be battery powered, what EVE features help me reduce power to maximise battery life?

EVE has several features which can help you maximise battery life. Many In-Home Displays for Smart Meters (and smart meters themselves) use battery power for portability (or due to the lack of a power source nearby). A combination of reducing the current drawn by the display and audio, putting EVE into low power modes and putting the MCU into low power modes can help maximise battery life.

One way to save power, even during use, is to dim the display via the backlight Pulse Width Modulation output. Your MCU could use an ambient light sensor and dim the backlight when full brightness is not needed, or it could have a slider on the EVE display itself to adjust brightness.

When the In-Home Display is idle and the display can be blank, the following steps can help to reduce power:

• Turning off the backlight completely by setting the REG_PWM_DUTY register to 0
• Setting all RGB output pins to low. This can be achieved by putting EVE into Power Down mode. If putting EVE into Standby/Sleep modes, the host MCU can set the RGB pins (including HSYNC/VSYNC/PCLK/DE/R[8]G[8]B[8]) to low by setting REG_HSYNC1=REG_HSYNC0 and REG_VSYNC1=REG_VSYNC0 and setting REG_PCLK=0
• Setting the capacitive touch panel controller (CTP) to a low power mode. For Focaltech CTPs this can be done via the ‘low-power mode’ bit in REG_TOUCH_CONFIG. For other CTPs, EVE’s custom touch feature can be used to implement the sleep/wakeup according to the CTP protocol found in its datasheet.
• Disable the external audio amplifier by selecting its low power mode via a GPIO from EVE.
• Disable the carrier wave on the EVE audio output pin by playing the mute sound via the sound registers.

The In-Home display can be woken up when the user touches the screen or when the MCU receives important data to display. The EVE Interrupt pin allows the MCU to easily determine when the screen has been touched.

Note: Capacitive Touch Panel controllers often have several modes with different current consumptions (e.g. active, monitor and sleep). They may not detect touches in some low power modes, check the datasheet of your selected touch controller.

Although the display (and audio) can account for most of the current, EVE also has low power modes which reduce the consumption of the IC itself to a minimum. Several modes are available to allow the best combination of power saving vs start-up time/actions to be chosen for the application.  These include the following modes (check the datasheet for your EVE device for specific details)

• Standby: The system core clocks are disabled but the crystal oscillator and PLL remain on and the register contents are retained.
• Sleep: The system core clocks, crystal oscillator and PLL are all disabled. The register contents are retained.
• Powerdown: The system core clocks, crystal oscillator and PLL are all disabled for even lower power. All register contents are lost and reset to default when the chip is next switched on.

The EVE Interrupt pin can be used to indicate touches to your MCU even when EVE is in low power modes, allowing the MCU to wake the display when the user interacts with the screen.