Cannot find I2C devices on ESP32

[l00p1n6]

Hello,

I am trying to make a display (128x32 I2C Pi OLED) to work with esp32 (ESP - WROOM-32)
OLED device is working properly as I have tested it with Arduino using Adafruit's libraries.
Esp32 device is working properly as it runs other code without problem.

I followed a video [https://www.youtube.com/watch?v=qqxgKZCTdUk] and was unsucessful in running the example code on MicroPython git site (https://github.com/micropython/micropyt ... ssd1306.py).
"i2c.writeto()" just kept timming out. It looked like I2C device was not found at all since scanning I2C returned empty list:

Code: Select all

import machine
i2c = machine.I2C(-1, sda=machine.Pin(21), scl=machine.Pin(22))
print(i2c.scan())

I have tried flashing latest stable firmware (esp32-idf3-20191220-v1.12.bin) but that did not help with I2C problem.

Does anyone have a clue on what I am doing wrong?

[Roberthh]

The code looks OK. So you should check the wiring (4 wires: Vcc, GND, scl, sda), whether the wires are not broken and the assignment to sda and scl.

[ESpy]

And make sure you really do rotate out the wires and don't just think you have (like I did...).

[l00p1n6]

Please find wiring attached:

https://ibb.co/L877QKT


https://ibb.co/QF0h1SN

One can see that the green wire is SDA.

NB: I did try to switch the wires on esp32 and got the same result

[Roberthh]

Did you also try to move the ESP32 on the breadboard or use other ESP32 pins for the test. You can use every output capable pin for SDA and SCL. Maybe either the breadboard is defective or the connection between the ESP32 chip and the pin connector.

[ESpy]

ESP32 has hw I2C, doesn't it, as opposed to the 8266? Haven't tried one as yet to see what the configuration differences might be.

That Vcc on the Arduino's definitely 3V3 isn't it?

[Roberthh]

The ESP32 has a hardware I2C, but when the I2C constructor with device ID -1 is called, the software I2C is used. That is done here. But I ran a SSD1306 both with software and hardware I2C. At least the scan function should return the address.

[Roberthh]

SO I looked at the schematics of the Arduino Mega and the Oled Pi device.
The Arduino has 10k pull-up resistors on SCL and SDA. The Oled Pi device has NO pull-up resistors.
So you have to add pull-up resistors to SCL and SDA. 4.7 kOhm is a good value. The ESP32 built-in weak pull-ups are not sufficient. It may work with a very low baud rate, like 10000 or 1000. At least for a scan that could give a result.

[l00p1n6]

Thank you Roberthh!
Your pullup idea did the trick:


https://ibb.co/4jNZDvw

NB: I didn't have 4.7k so I had to use 10k and 9.1k in parallel which gave me 4764 Ohm.

[rpr]

Thank you Roberthh!
Your pullup idea did the trick:


https://ibb.co/4jNZDvw

NB: I didn't have 4.7k so I had to use 10k and 9.1k in parallel which gave me 4764 Ohm.

Nicely done.