128x32 OLED Goes Dark w/ Added GPIO Board

The project is a systems simulation designed for use as a procedures trainer built on the Arduino Mega, using I2C and a broad spectrum of components including a variety of switch types, LED and FET-driven incandescent lights, rotary encoders, servos, SD audio, as well as the components pictured; PCF8574 GPIO breakout boards, and the TCA9548A I2C multiplexer driving multiple 0.91” 128x32 OLEDs.

When a 3rd PCF8574 GPIO breakout board is added, all 0.91 128x32 OLEDs that functioned properly before the addition of the GPIO board, cease to display (dark). All other components in the circuit work as designed, including those attached to the newly added PCF8574.

All I2C addresses are confirmed with a scan and no duplicates present. Error checking confirms all allocations are successful in the sketch including the SSD1306. I2C components are running off of 3.3v.

Libraries utilized in the sketch are as follows:
#include <Wire.h>
#include <PCF8574.h>
#include <Adafruit_PWMServoDriver.h>
#include <i2cEncoderLibV2.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#include <SD.h>
#include <TMRpcm.h>
#include <SPI.h>

Screen Shot 2021-02-02 at 9.35.27 PM.png

Screen Shot 2021-02-02 at 9.35.27 PM.png

If my memory is correct each of those boards has pull up resistors and you are overloading the I2C bus. If my memory is faulty then you need to add the pull up resistors. I like about 2K. I am assuming the power is stable when the unit is added.

Gil - Thanks for taking time to respond to my post.

Apparently the culprit in this little dilemma was the OLEDs [MakerFocus 0.91 Inch I2C SSD1306 OLED Display Module, White DC 3.3V~5V].

I resolved the issue and was able to get the circuit, as depicted, to function properly by replacing the MakerFocus OLEDs with PEMENOL 0.96 Inch I2C 128 x 64 SSD1306 OLED Display Modules. It’s not clear to me why that resolved the problem.

If anyone has some insight into why the MakerFocus LED’s went dark (or the PEMENOLs worked), as described above, I’d like to get a little smarter on this technology and avoid future problems Thanks.

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