Esp32 deep sleep and oled display

Other Hardware Displays
1

Here is what I want to do. A simple watch displaying the time as HH:MM each minute on an oled display, and put the esp32 in deep sleep during the interval.

Additionally, I want to update the display by changing only the digits that changed. For example, at time 05:17, I just want to change the 7, all the other numbers should remain on the display.

I use the library u8g2lib

But when the esp32 wakes from deep sleep, I have to declare and init the display, which erases it entirely. So this implies that I need to display the time completely.

Is there a solution to prevent the display from erasing?
Thanks for your help.

Edit. Oled display is for testing, my final objective is to use e-paper

2

Some display libraries write the screen output to a RAM buffer and then in a single operation write the entire buffer to the screen.

In other words does the library you are using allows a partial write to the screen (without an entire screen update) in the first place ?

3

I believe so. I've tried a simplified sketch doing the complete display in the setup and changing only one digit every 2 seconds in the loop. Works OK, but no deep sleep in this test, just some digit update.

4

I found this thread, that you may understand better than me (not native english speaker). I think it says that I can try to replace
display.begin();bydisplay.initDisplay();which would not empty the buffer.

what do you think ? Do you have the same understanding ?

5

As the ESP8266, ESP32 has some RTC non volatile Memory, so I think the right solution is to save , e.g. a boolean variable into the RTC non volatile memory ( e.g. RTC_DATA_ATT boolean InitDisplay) to tell the ESP32 that the display has already been initialized at the end of setup().

After waking up from deep sleep, there is a Reset and code runs from Setup(), not loop(). In setup(), test InitDisplay to initialize or not the display.

See this video, at 3:51 :

6

Thanks
I tried that already but the display remains frozen, it does not update

7

If deep sleep is not the solution, try light sleep. IMO in light sleep mode, after waking up, code runs from loop().

Of course current consumption should be higher:

8

If you are continuously displaying the OLED, that current will be way more than the sleep current of the ESP.

9

Paul__B:
If you are continuously displaying the OLED, that current will be way more than the sleep current of the ESP.

Yes, OLED is the display I use to design my code while waiting for e-paper displays.