Waveshare 2.9'' Epaper Panel + DESPI-C02 draws high current when powered off

[bbernhard]

Hi,

first of all, many thanks for maintaining that project and even more for being active and helpful when it comes to user questions. That's something that one doesn't see that often and therefore it is even more valued. Thank you so much!

I am using a Waveshare 2.9'' Epaper Panel, which I have disconnected from its PCB (to avoid the clever reset circuit) and instead connected to the DESPI-C02. This works really fine and the display gets properly updated. Now, before setting my ESP32 into deep sleep mode, I call GxEPD2's powerOff function. However, even after putting the ESP32 into deep sleep and powering off the epaper panel, the whole circuit still draws ~600uA. If I now manually disconnect the Waveshare Panel's power supply, the current consumption instantly drops to 80uA (since it is a bare bone ESP32 module without any LDO regulator nor USB, this is pretty much the deep sleep current of the ESP32 that I'd expect).

Initially I was using GxEPD2 version 1.5.2, but recently updated to the latest version (1.6.4) to see if that changes anything. Unfortunately, there was no change in that regard.

Does anyone have an idea why the panel is still drawing ~520uA, even after calling the powerOff function? Could that be a defective panel?

[G6EJD]

It sounds very much like a panel issue as the quiescent power should be near zero. How are you connecting the panel to the ESP32, it should only have the standard connections and no pull-up/down resistors etc.

[bbernhard]

Thanks for the fast reply!

Yep, the connection is standard - no pull-up/down resistors inbetween.

Do you (or anybody else) have some recommendations for a (Aliexpress) shop that is trustworthy and sells a 2.9" epaper panel that works with DESPI-C02? Using just the panel of a waveshare board again feels a bit wrong and wasteful.

[G6EJD]

The strange thing is, e-paper panels just don't/can't consume much power, so it must be faulty, unless it's a strange design where the display driver/controller remains powered and doesn't go to standby, or the standby command is different from most. It may be worth looking through the data sheet to see what its standby requirements are.

In my experience largely every supplier on AliExpress can't really be trusted, IMO many components are factory rejects or out of specification. The one exception is Waveshare or Gooddisplay which appear to be their respective outlet shops.

Good luck.

[ZinggJM]

Please note that powerOff() only switches off the booster circuit that produces the voltages needed to drive the panel's TFT layer.

For further reduced power use of the panel's controller, you would call hibernate().

If I now manually disconnect the Waveshare Panel's power supply...

I don't understand why you would provide power to the Waveshare board, when you only use the disconnected panel.

https://goodisplay.aliexpress.com/store/600281

[bbernhard]

Please note that powerOff() only switches off the booster circuit that produces the voltages needed to drive the panel's TFT layer.

For further reduced power use of the panel's controller, you would call hibernate().

If I now manually disconnect the Waveshare Panel's power supply...

I don't understand why you would provide power to the Waveshare board, when you only use the disconnected panel.

https://goodisplay.aliexpress.com/store/600281

Thanks for your reply and thanks for the aliexpress link!

Do I need to call both the powerOff and the hibernate? Tried to call both, but that didn't make any difference.

What I meant is, that if I remove the 3.3V supply from the DESPI-C02, the current consumption instantly drops.

[ZinggJM]

hibernate() calls powerOff().
hibernate() should make a difference. Maybe there is another cause.
Maybe you should post a schematics, showing what and where you measure.
And post a link to your ESP32 board used.

I suggest you call display.end() before putting the ESP32 to sleep, to set all pins used to INPUT, to avoid current flowing out.

[bbernhard]

Thanks!

And post a link to your ESP32 board used.

It's a custom board that I made- basically just a ESP32 with a few resistors and capacitors. Just the minimal amount to get the whole thing working. When doing the measurements, I am powering the whole thing with my laboratory power supply feeding in 3.3V. In series I have my ampere meter, which measures the current consumption.

I did some further testing and I think the epaper panel might indeed have some damage. If I slightly wiggle with the DESPI-C02 adapter and slightly twist and bend the fpc connection, the current consumption jumps from ~600uA to 1mA. I think it might be worth ordering another goodisplay panel and give that one a try.

edit: I also gave display.hibernate() and display.end() a try, but that also didn't change anything.

[bbernhard]

Sorry for the late reply, but today the GDEY029T94 that I ordered from Aliexpress came. Unfortunately the panel shows the same behavior as the other one.

Before the ESP32 goes into deep sleep, the current consumption is ~50mA. After the ESP32 goes to sleep, the current consumption drops to ~500uA. When I remove the +3.3V supply from the DESPI-C02 Board, the current consumption drops to ~50uA. So, for some reason the majority of the current seems to be consumed by the epaper panel.

My schematic basically (I am using a bunch of other GPIO pins of the ESP32 too, but I removed them from the schematics to focus on the important parts) looks like this:

This is the test program I am using:

#include <Arduino.h>
#include <GxEPD2_BW.h>

GxEPD2_BW<GxEPD2_290_T94, GxEPD2_290_T94::HEIGHT> display(GxEPD2_290_T94(/*CS=5*/ 26, /*DC=*/ 25, /*RST=*/ 33, /*BUSY=*/ 27));

void setup() 
{
	display.init(0, true);
	display.setRotation(1);
	display.setTextColor(GxEPD_BLACK);	
	
	display.fillScreen(GxEPD_WHITE);
	do
	{
		display.fillScreen(GxEPD_WHITE);
		display.setCursor(10, 10);
		display.print("Hello");
	}
	while (display.nextPage());
}

void loop()
{
	display.powerOff();
	display.hibernate();
	display.end();

	esp_deep_sleep_start();
}

Does anyone have an idea what else I could try?

In the DESPI-C02 manual I found this:

**4.6 High current in deep sleep mode**

The high current in deep sleep mode may be due to the larger
capacitance in the boost part.

Tips: The capacitor parameters in DESPI-C02 may be different
from the e-paper specification. So users need to strictly
refer to the component parameters in specification when
designing according to this circuit.

Could this be the reason? Does anyone have any experience with that?

[G6EJD]

When you remove the 3.3v supply how can you measure 50uA? If there is no potential difference there can be no current flow. It is very difficult to measure low currents without the correct methods and.suitable meters. The reference to capacitors will refer to buck converter values.

Have you turned off all GPIO pins that could be sourcing or sinking current.

when you disconnect the display your deep sleep current should be about 15uA, then with the display reconnected you should see an increase, do you. The display board may have a load that cannot be set to low power.

[ZinggJM]

The current seems to flow from the VCC pin of the controller to either GND or any of the IO pins.

Try to find out to where it flows, by disconnecting the IO pins one by one.
My guess would be either RST (internal pull-up?) or BUSY.

Make sure the FPC connector pins are correctly aligned, and the connector firmly inserted and fixed.