I’m trying to use a serial 7-segment display over I2C with Arduino UNO R3, both at 5V. As shown in the hookup guidance I only connected 5V/GND and SDA/SCL, with no other components. I was having trouble with dropped commands on the display. I saw discussions about I2C needing 4K7 pullup resistors. When I tried that the display showed garbage and became unresponsive. So what’s the story? Does the Atmel on the S7S already enable pullups, because they aren’t in the schematic? And if so, why would adding more pullups hurt? Maybe it enables pulldowns, and I was defeating them? When I removed the pullups it worked better, but is still dropping commands occasionally.
It depends on the device. The guide for the s7s doesn’t note any and I don’t see any when viewing the .brd file so I imagine they are likely not required. The issue superfluous ones can cause is too much resistance on the i2c bus, causing start/stop errors (hard to determine the differentials)
You might try messing around with delay timing and/or increasing the i2c bus speed