2
\$\begingroup\$

I'm a beginner trying to attach an OLED screen module made by Waveshare (schematic, datasheet of OLED screen) to my nRF5340 DK devkit (schematic sadly only available as part of a .zip file here) via SPI, but the display gives me dark horizontal lines of moving across it, even when set to full on white. Capturing it on video or photo is difficult:

Image of blurry lines

Connection of Board (see page 5 of schematics) -> OLED display:

  • P7.4 -> VCC
  • P7.7 -> GND
  • P5.3 -> DIN
  • P5.4 -> CLK
  • P3.7 -> CS
  • P3.6 -> DC
  • P3.5 -> RST

Image of entire setup: Image of the entire setup

Close-up of Waveshare OLED Board backside:

Backside of OLED module

As configuration data for the display I'm sending exactly what waveshare had in their sample code and as far as I could tell with a logic analyzer, this data is correct.

The only thing I'm aware of doing that may be out of spec is that my devkit is only providing 3V, instead of the minimum of 3.3V Waveshare lists on their website. Could this have damaged the display?

Trying to use it with an arduino afterwards with exactly the Waveshare sample code also led to the weird lines / flickering.

Update

I had a temporary fluke success where the display was fine after turning it over to look for whether I could probe the 15V line of the display cable, so my current hypothesis is that this may be a wiring issue. I will solder a pin header on the other side of the display tomorrow and get back to you.

Thank you all very much so far :)

\$\endgroup\$
8
  • 2
    \$\begingroup\$ I think an undervoltage of 0.3V is unlikely to have damaged your OLED, except perhaps if the I/O pins were driven higher than the power rail voltage. Was that the case? \$\endgroup\$ Mar 5, 2022 at 14:13
  • \$\begingroup\$ I don't think so, I just re-measured CS and VCC and both were almost exactly at 3V \$\endgroup\$
    – Andreas
    Mar 5, 2022 at 14:19
  • \$\begingroup\$ Where's the pdf data sheet for the LCD module? Note that items with only descriptions provided by web-pages leave you with no ability to track changes made by the supplier. This means that quality suffers and your LCD could easily be regarded as sub-standard materiel even when bought new. However, if you can provide a data sheet link.... \$\endgroup\$
    – Andy aka
    Mar 5, 2022 at 14:30
  • \$\begingroup\$ @Andyaka Thanks for pointing that out, I forgot to link that as well. It's waveshare.net/w/upload/c/c3/1.5inch_OLED_Specification.pdf, I now also added it to the question. \$\endgroup\$
    – Andreas
    Mar 5, 2022 at 14:33
  • \$\begingroup\$ You do not show your actual power supply or specs. for Vcc and 3.3V . Please update with more accuracy, photo , datasheet, whatever \$\endgroup\$ Mar 5, 2022 at 14:49

2 Answers 2

4
\$\begingroup\$

Where's the pdf data sheet for the LCD module?

@Andyaka Thanks for pointing that out, I forgot to link that as well. It's waveshare.net/w/upload/c/c3/1.5inch_OLED_Specification.pdf

Here's a section from the data sheet: -

enter image description here

enter image description here

As you can see, the power supply (\$V_{CI}\$) level can be from 2.6 volts to 3.5 volts so, maybe you forgot to provide the \$V_{CC}\$ supply of nominally 15 volts? Both supplies are needed but, as I can see in your schematic, it looks like you have provided the 15 volts via a boost converter.

The only thing I'm aware of doing that may be out of spec is that my devkit is only providing 3V, instead of the minimum of 3.3V Waveshare lists on their website. Could this have damaged the display?

No, that doesn't seem likely.

\$\endgroup\$
4
  • \$\begingroup\$ I'm using a premade OLED Module / Board which has only a single voltage input pin, the voltage regulation is handled by it as well, so I don't have any control over that. \$\endgroup\$
    – Andreas
    Mar 5, 2022 at 14:43
  • \$\begingroup\$ Try measuring the 15 volts to see that it is within spec @Andreas \$\endgroup\$
    – Andy aka
    Mar 5, 2022 at 14:46
  • \$\begingroup\$ I'm not sure whether I can probe on this fine display connector without shorting something, but after looking at it, I had a fluke attempt where after turning on the display again it did not have the travelling lines and also didn't whine. Could this behaviour also be caused by an intermittent power connection? \$\endgroup\$
    – Andreas
    Mar 5, 2022 at 15:13
  • 1
    \$\begingroup\$ @Andreas I don't see why not; most other random bad behaviours are easily caused by bad connections. \$\endgroup\$
    – Andy aka
    Mar 5, 2022 at 15:23
0
\$\begingroup\$

The horizontal lines look like power supply ripple. Assuming the screen scans from top to bottom, the pixels are getting dimmer and then suddenly getting bright again. Which is the sort of waveform you would expect from power supply ripple.

I gather that the display uses an 8-19V high voltage supply for the display, and the Waveshare circuit board has a boost converter which provides this. In which case, is there something wrong with the output capacitor? I can't tell which component that is.

You say that it worked after fiddling with the module a bit - perhaps a cracked solder joint making intermittent contact?

The whining noise could also be a symptom of a problem with the boost converter. Usually they run at a frequency too high to hear, but if the output current is too low, they will reduce the frequency and run in so-called "burst mode".

Or perhaps the Waveshare module is struggling to get power itself for the converter. You could check the voltage at the input pins - is it enough?

Long wires can sometimes have too much inductance for reliable high-frequency operation - essentially when the module draws power the power can't get there fast enough and the voltage drops. You can try adding more capacitance directly at the power input of the Waveshare board, although boost converters should have reasonably steady input current so I think this is unlikely to be the problem.

Either way, in my opinion all signs point to a power supply problem. If you have an oscilloscope you can try to probe the 8-19V power supply of the display. I bet it's got too low a voltage and too much ripple.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.