Issues trying a 128x64 OLED screen through I2C

groumpf

Hi, first thanks a lot for the Bela platform and the community. It's a wonderful way for me to get into electronic and to continue to learn more stuff !

I just bought a 128x64 OLED screen 2.4" from Adafruit (https://www.adafruit.com/product/2719) which I'm trying to connect using I2C.
I tried following this topic : https://learn.bela.io/using-bela/bela-techniques/using-an-oled-screen/
and the instructions on how to set the screen in I2C mode here : https://learn.adafruit.com/1-5-and-2-4-monochrome-128x64-oled-display-module/wiring-and-test#i2c-wiring-2788112

First I soldered the back of the screen into I2C mode.

Then I hooked up on my breadboard in the following way :

You can notice I didn't wired the RST pin (unlike shown in the Adafruit tutorial, with the voltage dividing resistors : because I don't yet understand how it works and I've read it would only prevent me from printing sometimes, but it should at least display some noise. Also, as suggested in the Adafruit tutorial I added a 120µF capacitor to help smooth the voltage.

Then I grabbed this example (as suggested in the Bela topic on OLED screens) to test it : https://github.com/giuliomoro/O2O
In my case the driver chip is a 1305, so I changed this code

std::vector<Display> gDisplays = {
	// use `-1` as the last value to indicate that the display is not behind a mux, or a number between 0 and 7 for its muxed channel number
	{ U8G2_SH1106_128X64_NONAME_F_HW_I2C_LINUX(U8G2_R0, gI2cBus, 0x3c), -1},
	// add more displays / addresses here
};

for this code

std::vector<Display> gDisplays = {
	// use `-1` as the last value to indicate that the display is not behind a mux, or a number between 0 and 7 for its muxed channel number
	{U8G2LinuxI2C(U8G2_R0, gI2cBus, 0x3c, u8g2_Setup_ssd1305_i2c_128x64_adafruit_f), -1},
	// add more displays / addresses here
};

But when I try to run the example, nothing happens on the screen and I got the following error messages :

Running project ...
opened i2c file 3
set i2c addr 3c
can't write cmd 40: Remote I/O error
can't write cmd 40: Remote I/O error
can't write cmd 40: Remote I/O error
can't write cmd 0: Remote I/O error
can't write cmd 0: Remote I/O error
... // repeats continuously

When I try to check the I2C address on the cli, sometimes the adress is there, sometimes not (I didn't changed anything between the commands, just waited a few seconds) :

I'm really new to these topics so I'm a bit lost I must admit ^{^"} would anyone have an idea on what could have I done wrong ?

Just for the context :
- I checked the pins of my screen with a multimeter, no issues
- I use the multiplexer in my project, so I wanna try with it directly
- My bela runs on v0.3.8g
- Because of the multiplexer I had to add a 3.3V 10k pull-ups on the SPI pins as suggested in various forum posts

groumpf

EDIT : I tried removing the multiplexer caplet, nothing changed.

Then I tried to add a RST connection, either pulling it up or down, in both cases it ended never showing the I2C adresse at all (whereas before I had it quite randomly sometimes when running i2cdetect

giuliomoro

the datasheet says

alt text

so you should connect it to 3v3 via, say, a 2k2 resistor. Then you can try the following:

short the pin to ground
remove the short
run i2cdetect : does it respond?

Repeat this a few times and see if i2cdetect starts working regularly.

groumpf

It worked like a charm ! Thank you so much 🙂 The example runs smooth with a pretty BELA printed on the screen.

I guess it means I should connect RST to a GPIO (or a digital pin ?) and set it to GND then VDD at the very start of my program ?

Also (out of curisity) : during my reseach I found out many different post about how to connect through I2C to an OLED screen. None of them mentioned using OSC (which I don't know that much about).

Is it something mandatory ? What would be the pros/cons of using OSC over I2C ? Would you have any recommended readings about it 🙂 ?

if you don't have that much time to get into details no worries, you already helped me a lot -

giuliomoro

groumpf I guess it means I should connect RST to a GPIO (or a digital pin ?) and set it to GND then VDD at the very start of my program ?

Yes, this would work. You can use the Gpio class : https://docs.bela.io/classGpio.html (make sure at every startup you set it to low, sleep a few milliseconds and switch it back to high).

groumpf Is it something mandatory ? What would be the pros/cons of using OSC over I2C ? Would you have any recommended readings about it 🙂 ?

OSC is a protocol that is fairly diffused in the audio world (e.g.: Supercollider uses OSC to communicate between the frontend and the audio server). The examples we provide do not use OSC over I2C (as OLED displays don't know anything about OSC), rather there is a little OSC server that receives OSC from "wherever" and converts these messages into commands to be sent directly to the screen. This allows you to use it with programs such as Pd or Supercollider which can send OSC messages without any C++ programming. If you have a C++ program already, you may not need to use the O2O server and you could integrate the message sending to the I2C display directly in your code.

groumpf

That's what I finally understood from reading the example code this past days, thanks for the confirmation !