I am going to use https://www.waveshare.com/wiki/E-Paper_ESP32_Driver_Board with 7.5 inch e-Paper module. It will be powered by single 18650 battery. For the most of the time it should be in deep sleep mode to save battery life.
How should I power a Driver Board? Should I use step up converter -> 5V and connect VCC to Driver's 5V pin or should I use step down converter -> 3.3V and connect VCC to Driver's 3.3V pin?
Which one of above (if any) methods will be most stable and efficient?
...bnd one more related question: is there any software method to turn of Driver's power led?
I should be a bit more cautious when recommending this driver board for low power use, as I never measured the current drawn for processor deep sleep. So I don't know how relevant that led is. And I see it glowing on the backside of one of my displays, that is used with USB power.
I don't know the power used by step-up or step-down converters, under no load.
It may be higher than what the processor takes while in deep sleep.
For my SHT31 with ESP8266 sensor nodes, I connect 4 NiMH batteries or one 18650 battery directly to the 5V pin, and measure the voltage. Send the processor to sleep when below 4.2 or 3.5V. This can use about half the capacity of a 18650.
-jz-
Thanks for quick response!
I think I will try to do it your way then. With 4 rechargeable AA. That should give voltage acceptable by the board (according to its board's WIKI it should be 3.6-5.5V).
I will connect the set directly to GND, 5V pins.
When have a chance (currently my multimeter is broken) I will measure the current in deep sleep mode and put it here.
@ZinggJM as I promised, I have measured the current and it was 1.4mA in deep sleep mode. Then I decided to solder out power led and after I did this, current decreased by a half to 700 micro amps. Most of this might be taken by driver board's step down converter, but I am only guessing - didn't try with seperate converter and powering 3.3 V.
700 micro in deep sleep and 60 mili when active (~30-40sec. per hour) gives me approximately 2 months per one charging (4xAAA 2000mAh). Fair enough for me!
BTW: I have also added a voltage divider to monitor the state of batteries. What do you think - what is save voltage drop for both - the board and the batteries? Waveshare's wiki says 5V pin supports 3.6V to 5.5V voltage input my guess is to force charging somewhere around 4.4-4.6
I use 4.2V for 4 NiMH, to avoid deep discharge.
I use 3.5V for LiPo 18650, to allow for voltage drop of LDO. Would use 3.7V for use with large display instead of sensor node.
My sensor nodes report every 3 minutes. Need recharge about once a month.
Never had time for further investigation or improvement.
I would use 2 18650 or 26650 instead, with a step-down converter. But would need to check its idle current first.
-jz-