ePaper Display (28084)

I'm enjoying playing with this display wired to a FLIP; have displayed large fonts, different orientations, random numbers, programs running from EEPROM.

However, I may have already partly damaged it. When the display toggles from "white paper" to black, there are multiple vertical white lines in the black.

The Product ID 28084 Details Key Specifications page says "Operating voltage: 3.3V/5V".

I took this to mean the display would operate on either 3.3 volts or 5 volts. But when connected to the FLIP USB5V pin, nothing on the display at all. Does not do the black / white / black / white routine when powered up to get rid of ghosting. My multimeter shows this pin to have 5 volts. Then when hooked back to the FLIP 3.3 volt pin, it works.

The Waveshare Specifications page 17 Maximum Ratings says: "Logic supply voltage -0.5 to +4.0 volts." This makes me think the device should be connected only to 3.3 volts.

Comments

  • I may be wrong about not using 5 volts. In the Waveshare User Manual it states under Specification "Operating Voltage 3.3V/5V (but keep all input pins the same, either 3.3V or 5V.

    The weird thing is, all examples given by Waveshare (Pi, Arduino, STM32) say to hook the module up to 3.3 volts.

    It might be that the module has a chip on it to convert incoming 5 volts to 3.3 for the ePaper "raw panel" as they call it but I cannot tell since the chip looks proprietary.

    I tried again using the USB 5V FLIP pin and still nothing. Then tried 5 volts from my Rigol (gnd to FLIP gnd, 5v to ePaper Vcc). It worked for a short time and then stopped. Before it stopped it displayed a thick white band about 2/3 down the display against the black, like it could not be refreshed correctly.

    After which it would not work on the FLIP 3.3V. After disconnecting and letting it sit for 5 minutes, it now again works from the FLIP 3.3V.

    Perhaps I need to rewire on a different breadboard with different wires to see if there is some sort of intermittent. Or perhaps this specific module really does not like having 5 volts applied ???
  • I think that it may indeed not be liking having 3.3v logic while connected to 5v power. Maybe it causes partial logic switching(brownout).
    Windows 10 Home:
    Propeller Tool 1.3.2, BASIC Stamp Editor 2.5.4, Javelin Stamp IDE x.x.x, Arduino IDE, PST
    Hardware:
    BASIC Stamp Board of Education, Propeller Board of Education, Propeller Project Board, Propeller Mini
  • Since supply voltage and I-o voltage should be the same as stated, and Propeller I-O is 3.3v my guess is you should use 3.3v not 5v.

    Mike
    I am just another Code Monkey.
    A determined coder can write COBOL programs in any language. -- Author unknown.
    Press any key to continue, any other key to quit

    The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this post are to be interpreted as described in RFC 2119.
  • Ken GraceyKen Gracey Posts: 6,429
    edited 2019-08-05 - 17:09:05
    From David Carrier, on an internal communication:

    The schematic for the ePaper module is posted here: https://www.waveshare.com/w/upload/8/85/2.9inch_e-Paper_Schematic.pdf. It uses a TXS0108E level converter, which has a set of 'A' pins for the lower-voltage device and a set of 'B' pins for the higher-voltage device. The 'B' pins are connected to the external I/O and have an absolute maximum voltage rated at 6.5 volts, regardless of Vccb. They do have a recommended high input voltage of Vccb, but signals exceeding Vccb, while still under 6.5 volts, should not cause any damage, although it could cause undesired operation.

    So, it doesn't seem that 5V input is a problem. This is a Waveshare-supplied product, as you noted.

    I'd be happy to replace it for you. Contact me offline for an RMA kgracey@parallax.com

    [update: according to Michael your display is working, so disregard this message. But, if anybody ever needs service from us just say something. I don't often monitor the forums so feel free to draw my attention to possible RMA issues quickly via email kgracey@parallax.com]

    Thanks,

    Ken Gracey
  • Another example of Parallax’s amazing customer service! Always there!
    Windows 10 Home:
    Propeller Tool 1.3.2, BASIC Stamp Editor 2.5.4, Javelin Stamp IDE x.x.x, Arduino IDE, PST
    Hardware:
    BASIC Stamp Board of Education, Propeller Board of Education, Propeller Project Board, Propeller Mini
  • Thank you for all the responses. I'm convinced my ePaper display is working at 3.3 volts. And I'm convinced that the weird behavior I saw at 5 volts was due to USER error; I ignored keeping signals and Vcc at same voltage.
    I will investigate this more. But thanks to all.
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