Can't get SH1106 1.3 oled to work (SPI)

Question

It's my first project this big - an arduino (Pro Micro) based midi controller. After all the research, schematics and pcb designing I got to assembly and wanted to try out the display, but then I can't get it to work!

Example code, from recommended u8g2 lib is:

#include <Arduino.h>
#include <SPI.h>
#include <U8g2lib.h>
const byte clock = 15;
const byte data = 14;
const byte cs = 9;
const byte reset = 8;

U8G2_SH1106_128X64_NONAME_F_3W_SW_SPI u8g2(U8G2_R0, clock, data, cs , reset);

void setup(void) {
  SPI.begin();
  u8g2.begin();
}

void loop(void) {
  u8g2.firstPage();
  do {
    u8g2.setFont(u8g2_font_ncenB14_tr);
    u8g2.drawStr(0,15,"Hello World!");
  } while ( u8g2.nextPage() );
  delay(1000);
}

Tried all the listed constructors, SW HW, all the models and buffer sizes. I run the connections to the display through TXS0104EDR logic converter (SMD, so prototyping off-pcb seems not doable, but maybe I should try?)

Maybe from all the components power draw, 5V actually measures 4.65V. Voltage divider (5k,10k) when connected to the load measured ~0.8V, so I swapped it for a 5k potentiometer to set the voltage manually to 3.3V

I can't figure out what I'm doing wrong.

---

So I just swapped the voltage divider for a LD33CV regulator, still nothing.

I'm Starting to wonder if it's not a model suited only for 4pin communication. In the documentation, some manipulation is needed to work in 3pin mode: IM0 pulled up, DC pulled down, but here's my chip, no IM0 connection:

Where do you think I should go from here? My ideas:

• Wire a 5v logic signal from let's say A2 to D/C input
• Swap 3.3V CS for D/C, pull CS always low (then somehow omit soft pin requirement)
• Get a different screen capable of 3pin?

Update: I risked one chip, wired all in 5V logic and it worked! :) My first idea, with 5v D/C signal also worked on the pcb. However tivial, this feels like a win :) It's my first time posting here, so thank you all for support

But some question remains: Why is it working only in Software-emulated SPI mode? when i change the constructor to hardware(no clock and data pins specified), no more. It seems very time-inefficient. loop like this:

t = millis() - last;
  last = millis();
  u8g2.clearBuffer();
  u8g2.setFont(u8g2_font_ncenB14_tr);
  u8g2.setCursor(0,20);
  u8g2.print(t,10);
  u8g2.sendBuffer();

displays around 15 ms.

Answer 1

Two reasons why the hardware SPI does not work for you.

Arduino pin 16 is the hardware SPI MOSI data output, but in your schematic you use Arduino pin 14 which is the hardware SPI MISO data input.

In addition, the SPI hardware SS pin is used for onboard LED. That's fine as any pin can be used for SS in software, but the hardware SS pin must still be set as output. If the hardware SPI SS pin is left as an input, expect problems, as the hardware SPI will drop from master to slave mode when SS is input and it goes low. And it can't even be used as input with internal pull-up, because the LED will load it down to logic low.