ESP32 Forum

ePaper panels have a fairly long update delays (1 to > 4 seconds). It would be nice conserve power during the wait.

When I enable automatic light sleep, esp32 is no longer able to communicate with the ePaper panel. My guess is that the GPIO pins either float during sleep or go to 0 including the reset pin to the ePaper and mess things up.

I tried using to hold the gpio control lines to the ePaper module during sleep.

Did this by calling before delay operations that can lead to light_sleep and after.

The confusing bit in the docs is that https://docs.espressif.com/projects/esp ... gpio_num_t only talks about deep sleep behaviour of and not light sleep


I'm also not sure what would happen to the SPI lines and config power wake up from light sleep.

Thanks!

I'm also interested to know more about this.

One question though, reading the manual it says:
In light sleep mode, digital peripherals, most of the RAM, and CPUs are clock-gated, and supply voltage is reduced.

That if I understood well is that SPI transmission stops right, but after you send the Pixel buffer to an epaper, and the update command...supposely, it should render provided that the 3.3 v supply is still there.
However it calls my attention, that after the update that as you mention takes about 2-4 seconds, usually most components send the display module to sleep. Avoiding to that will make consumption even bigger, surpassing the 4 seconds savings you are mentioning (In my humble opinion)

Just because is related, I wanted to invite you also to test my ESP-IDF component for epaper, where you can customize in detail any of this SPI communication and modify it per display model easily:
https://github.com/martinberlin/cale-idf - Full test implementation with BMP download

https://github.com/martinberlin/CalEPD - Just the ESP-IDF component (Note: Needs Adafruit GFX in order to use Fonts/Geometric functions)