I configured a scale with HX711 and made a mailbox that notifies me when there is mail. By replacing the regulator with a DCDC converter and the USB serial with CH340 in the ESP32-DevKitC used in this device, I was able to reduce the current consumption during DeepSleep to 0.02mA.
For more information about saving power during DeepSleep on ESP32-DevKitC, please refer to here.
Power down mode of HX711
The HX711 has two modes of operation: normal mode and power down mode, which can be enabled by setting the clock pin communicating between the HX711 and the ESP32 to high.
According to the datasheet, the HX711 consumes about 1.5mA in normal operation, but in power-down mode, it can be reduced to 0.5uA.
This is the block diagram of the mailbox notified by email so far.
The current consumption during DeepSleep in this state was 4.13mA.
Putting it into power-down mode
Add a pull-up resistor so that the clock signal of the HX711 can stay high during DeepSleep.
The block diagram looks like this. I just added one resistor.
The current consumption during DeepSleee in this block diagram is now 0.12mA. This is not quite the 0.5uA shown in the datasheet, but the current has been reduced from 4.13mA to 0.12mA, or about 1/40th.
Before I took the ESP32-DevKitC power saving measures, this device was consuming about 15mA even during DeepSleep, and when I added the ESP32-DevKitC power saving measures and this power down mode measure, the current consumption was reduced to 1/100. This will further extend the life of the mailbox in battery operation.
I'd like to keep it running and see how long it can run on three rechargeable batteries.