Missing example EPD_7in5bc_V2

[Ziesie1]

Hello,
which example in the folder "Arduino/" is the correct version for this e-paper?

As per the documentation it should be the "EPD_7in5bc_V2" example. The name is also listed in the Arduino/README.md file but no corresponding folder could be found.

The example in epd7in5b_V2 didn't work for me. It hangs during initialization in WaitUntilIdle().
I have the 7.5 inch model V3 and the HAT Rev2.2.

[SSYYL]

epd7in5b_V2 is applicable to your screen.
Note that you need to select "4-line SPI".

[Ziesie1]

Thank you for the response.
"4-line SPI" is selected and all connections were checked twice.

With a logic analyzer I can confirm the following behavior:
After the command POWER ON (04h) the busy pin of the display goes low but never comes high again. This is why the mcu hangs in the WaitUntilIdle() loop.
What does this mean?

I am also wondering why in the example epd7inb_V2 the command 71h is being sent during WaitUntilIdle().
This command is not listed in the datasheet?

[matthias-bs]

Hello,
I am encountering the same problem as @Ziesie1. I am trying to use the same display with the WaveShare e-Paper ESP32 Driver Board.

[matthias-bs]

I found the following hint in the FAQ: Question:Why is the BUSY pin always busy?, but the answer does not really help me to understand the problem.

[matthias-bs]

Another weird thing: normally, the ESP32's HSPI interface is wired as follows (see https://github.com/espressif/arduino-esp32/blob/master/libraries/SPI/examples/SPI_Multiple_Buses/SPI_Multiple_Buses.ino):

SCLK - GPIO14
MOSI - GPIO13

but on the WaveShare e-Paper ESP32 Driver Board - according to the Wiki pin list and the schematic - we have:

SCLK - GPIO13
MOSI - GPIO14 (SDI)

[matthias-bs]

And maybe because of this, SPI transfers are implemented by bit-banging in the ESP32 Driver Board examples (see DEV_Config.cpp).

[Ziesie1]

My display is probably broken.
I also tried the raspberry-pi implementation (link), but here I had the same problem with the busy pin.

[matthias-bs]

I tried the MicroPython version from https://github.com/tanahy/micropython-waveshare-epaper today - https://github.com/tanahy/micropython-waveshare-epaper/blob/dev/epaper7in5_V2.py to be precise. I tweaked the pin configuration a little bit to adapt to the WaveShare e-Paper ESP32 Driver Board and got the following results:
Ch 0 - brown: SCLK
Ch 1 - red: nCS
Ch 2 - orange: SDI
Ch 3 - green: nBusy
Ch 4 - yellow: DC (i.e. Data/nCommand)
Ch 5 - blue: nReset
"3SPI 0" is the decoded 3-wire SPI bus.

Reset pulse:

Then we have got the begin of the init sequence:

1. Command POWER_SETTING (0x01)
2. Data 0x07
3. Data 0x07
   

...
4. Data 0x3F
5. Data 0x3F
6. Command POWER_ON (0x04)
After the POWER_ON command, nBusy turns low and remains low.

Repeat:
7. Command GET_STATUS (0x71)
8. Poll nBusy

Any ideas?

[matthias-bs]

test.py:

"""
	Example for 7.5 inch black & white Waveshare E-ink screen, V2
	Run on ESP32
"""

import epaper7in5_V2
from machine import Pin, SPI, SoftSPI

sck = Pin(13)
miso = Pin(12)
mosi = Pin(14)
dc = Pin(27, Pin.OUT)
cs = Pin(15, Pin.OUT)
rst = Pin(26)
busy = Pin(25, Pin.IN)
spi = SoftSPI(baudrate=20000000, polarity=0, phase=0, sck=sck, miso=miso, mosi=mosi)

e = epaper7in5_V2.EPD(spi, cs, dc, rst, busy)
e.init()

w = 800
h = 480
x = 0
y = 0

# --------------------
[...]

[matthias-bs]

I also tried to changed the baudrate to a lower value, switched the display type (A/B) and used an external 3.3V power supply - to no avail.

[matthias-bs]

I just found the following PR: #193
After changing EPD_7in5b_V2.cpp accordingly - as follows - I got something on the display!

/******************************************************************************
function :	Wait until the busy_pin goes LOW
parameter:
******************************************************************************/
void EPD_7IN5B_V2_WaitUntilIdle(void)
{
    Debug("e-Paper busy\r\n");
    volatile unsigned char busy;
        int iter = 0;
	do	{
                //EPD_7IN5B_V2_SendCommand(0x71);
		busy = DEV_Digital_Read(EPD_BUSY_PIN);
		busy =!(busy & 0x01);
                DEV_Delay_ms(100);
                if (iter++ > 150)
                    break;
	} while(busy);
	DEV_Delay_ms(200);      
        Debug("e-Paper busy release\r\n");
}

So, instead of waiting for the Busy signal to become de-asserted, the wait loop left after a timeout. And the SendCommand(0x71) (GET_STATUS) does not seem to be necessary.

[matthias-bs]

I ordered a second display (this time 7.5 inch T7, i.e. black/white) and a second WaveShare e-Paper ESP32 Driver Board.

Now I found out that

• My first WaveShare e-Paper ESP32 Driver Board is broken
• The example code "epd7in5b_V2-demo" from E-Paper_ESP32_Driver_Board_Code.7z works with the 7.5 inch black/white/red display (type DEPG0750RW) as stated above

[Ziesie1]

That's how it was for me, too @SSYYL.

The new display is now running fine with the example code.