[SSD1306] "No I2C devices found"

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Winfried
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[SSD1306] "No I2C devices found"

#1 Post by Winfried » 20 Apr 2022, 17:43

Hello,

Following those instructions, the SSD1306 OLED display is connected to a NodeMCU controller with 3V3+GND pins for power (this display uses 3,3V), and SCL-D1 + SDA-D2 for communication.

I checked with a multimeter that there's indeed 3,3V volts on both ends (controller and display.)

But when hitting Tools > I2C Scan in ESP Easy, it says "No I2C devices found".

I made no change to the default settings.

Since the product page says "D1-SOA" and "D2-SCL", I unsoldered and swapped the two wires, still no go.

As shown the Senseair CO2 sensor works OK.

Could it be the screen is simply dead?

Thank you.
NodeMCU.SSD1303.no.display.png
NodeMCU.SSD1303.no.display.png (59.36 KiB) Viewed 4909 times

TD-er
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Re: [SSD1306] "No I2C devices found"

#2 Post by TD-er » 20 Apr 2022, 18:03

Instead of desoldering the cables, you could also simply swap the pin configuration in the ESPEasy config.

It is always possible the display is defective, but to be honest, those small OLED screens are quite reliable.
The only ones I've seen that were broken, were actually literally broken.

There are however different versions out there, which have the GND and VCC swapped, but their printing on the silkscreen was always correct.
It does make a difference though, when you try to plug those in an existing PCB as swapping Vcc and GND will very likely fry the electronics of the display.

What you can test, is trying to run the I2C bus at a lower frequency of 100000 (100 kHz), which you can set on the page you showed in your screenshot.
If you are using long cables for SDA and SCL, you may get strange issues and running at a lower clock frequency may help in the diagnostics.

Winfried
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Re: [SSD1306] "No I2C devices found"

#3 Post by Winfried » 20 Apr 2022, 21:41

Thanks for the tip.

Forgot to say the display did work fine before. I simply removed the Dupont wires I used as a test, unsoldered the pins, and soldered permanent wires to get a more compact setup. So the VCC+GND pins are OK.

In the Hardware page, I changed the Clockspeed from its original 400000 to 100000, submitted, rebooted, and tried again the Tools > IC2 Scan: It still stays "No I2C devices found" :-/

Maybe my soldering isn't good enough, and the board can't communicate with the display. It's strange because I see no moving part, and the CO2 sensor works OK.

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Re: [SSD1306] "No I2C devices found"

#4 Post by TD-er » 20 Apr 2022, 21:56

Not sure why you refer to the CO2 sensor, as that one is using serial, not I2C.
Also the CO2 sensor needs 5V where the display needs 3.3 V.

Maybe double-check to see if there is not some kind of short in the soldering, or worse, some damaged PCB trace due to heating the pads for too long.

Winfried
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Re: [SSD1306] "No I2C devices found"

#5 Post by Winfried » 20 Apr 2022, 22:36

I mentioned the sensor because it means the NodeMCU works and I managed to solder at least six wires OK.

I'll re-solder the two wires between the controller and the display, since it seems to be the probable reason for the issue.

Thank you.

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