Keep display turned off after waking up

Hi! I want to use the SoM for reading sensor data periodically while reducing the power consumption. The data is displayed on the Toradex 7 inch capacitive touchscreen.

In order to achieve this, I will use the suspend and wakeup capabilities of the SoM. However, I’ve noticed that the display turns on after the module wakes up and I need it to be off to reduce power consumption.

Currently, I achieve this by immediately turning off the screen in my application, as you can see from the following Python code:

os.system("echo +10 > /sys/class/rtc/rtc0/wakealarm") # Set wakeup time
os.system("echo mem > /sys/power/state") # Enter suspend mode for lowest possible power consumption
os.system("xset dpms force off") # Turn off screen immediately after returning from the suspend mode

The problem is that the screen flashes just before the xset command is given and I would like to avoid this, because it is not needed.

Is there a (better) way to do this? Also, is it possible to turn off the screen completely and turn it on again when required? (e.g., during the suspend period, nothing is displayed, whereas using the xset dpms force off just turns off the backlight, but the image is still visible, and has the same behavior as echo 0 > /sys/class/backlight/backlight/brightness)

HI @CristianM ,

You could try to turn off the display altogether, when it is a viable option to you.
To do so, you need to write 0 to the pin 5, as mentioned in Page 11/27 of this manual

Best Regards,

Hi. Pin 5 turns off only the backlight, not the display altogether.

I did as you suggested, but the image is still displayed (it is visible in good ambient light conditions) so that is why I was asking if it is possible turn off the screen completely (e.g., in suspend mode no image is displayed → the screen is turned off completely). Do you have an idea how to do this?

Anyway, your suggestion helped, because if turn off the backlight before entering suspend mode, the screen does not flash upon waking up.

Hello @CristianM ,

As the display does not have a separate power off button, you cannot turn off the display unless disconnected. Turning the backlight would be the way to go

Best Regards,

I understand. But how does the suspend mode turn it off completely?

In the suspend mode, the module gets in the low power mode and the peripherals are turned off. And that’s why the power to the display is also turned off

Ok. So is there a way to manually turn off the LCD peripheral and turn it on again when needed?

Hi @CristianM ,

The Display is always ON when it is plugged in to the power source. In your case the carrier board.
So, if you need to turn the display off, you need to unplug it

OK. So I understand from you that manual control of the LCD peripheral is not possible. Turning off this peripheral can be done in software only by using the suspend mode (maybe also standby mode, but I haven’t tested). Otherwise, it can be done in hardware by controlling the display power rail.

Yes, you are right!