GxEPD2 Loss of contrast. Waveshare e-Paper Driver HAT rev2.3

Other Hardware Displays
1

This issue is being reported by multiple users and contributors to the esp32-weather-epd project on github originally reported here.

Recently, waveshare has updated their driver HATs from rev2.3, which are shipping with their 7.5" BW display (sometime in late august?).

The revision includes the following changes outlined here. I have translated to English using google translate.

Version changes:

The RST pin now only controls reset and no longer controls power on and off.
Add a PWR pin to control power on and off
Replace the inductor with a smaller, thinner package
PH2.0 8Pin interface replaced with GH1.25 9Pin interface

If you need to upgrade to this version from a previous version, you can choose one of the following methods for compatibility:

Update the program to the latest (Arduino program only supports 7.5inch e-Paper, 7.5inch e-Paper (B), 5.83inch e-Paper, 5.83inch e-Paper (B), 2.9inch e-Paper (D), 2.13 inch e-Paper (D) six screens)
Connect PWR pin to 3.3V
Solder a 47K (or similar) resistor to the empty pad on the back

Our current solution for users receiving the rev2.3 screen has been to Connect PWR pin to 3.3V.

This seemed to work initially until users had rainy days (literally). The esp32-weather-epd project draws a chart using dithering that displays Probability of Precipitation. On days forecasted with lots of rain, there is a significant amount of dithering used which causes a loss of contrast across the entire display (shown below).

1476×979 280 KB

Our users were further able to confirm that the issue occurs only with the rev2.3 HAT by getting a hold of both the rev2.2 and 2.3, and swapping between the two.

@ZinggJM

2

I made a post on the Arduino forums, which (I think) is his preferred contact method for GxEPD2 related questions.

Yes, it is. But why do you think this issue has anything to do with GxEPD2?

I may take a look at it, if I get complete information. Link to the display, processor used, constructor line, inking found on the flexible connector. Voltage supplied to the HAT.

Did you ask Waveshare if their new HAT can produce strong enough panel driving voltage and power for a 7.5" display, with their smaller inductor?
-jz-

1 Like
3

Thanks for the reply.

Not sure if this has anything to do with GxEPD2, other than it is the display library being used. I was mostly just wondering if you have seen this issue before. I'm not entirely sure why this may be happening, and was hoping that you might have any insights.

Here is the information you requested.

ESP-WROOM-32E - specifically this board https://www.dfrobot.com/product-2195.html

  GxEPD2_BW<GxEPD2_750_T7,
            GxEPD2_750_T7::HEIGHT> display(
    GxEPD2_750_T7(PIN_EPD_CS,
                  PIN_EPD_DC,
                  PIN_EPD_RST,
                  PIN_EPD_BUSY));

Here is a wiring diagram. The HAT is wired to 3.3v.

image
image1670×1080 142 KB

Working on getting a picture of the inking.

That's a good question, I will forward it to Waveshare. So this presents like a low voltage issue?

-Luke

Edit: added constructor

4

I don't understand why some users still use a HAT with level converter with 3.3V processors.
Especially for low power use, e.g. running on batteries.
Readers of my responses know they should use DESPI-C02 instead.

Yes, I had the same issue with the older HAT on some ESP32 or ESP8266 that had marginal 3.3V.
-jz-

5

I wasn't aware there was a better solution. Thanks for sharing. I will recommend that going forward.

6

This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.