Arduino Oled 0.91 and tca9548 problems

Hi. I’m making bike computer with GPS, and everything was going great, until I re solider oled pins. Now one screen shows text from both. I checked connections , and everything looks to be the same as before changes . Im using 0.91 oleds which are connected to tca 9548A i2c splitter. When I connect second oled to first one sda and scl , second one shows text from both, and first show nothing , so it is not oled problems. When I connect this screens to arduino, without tca i2c scanner is stuck at scanning (it doesn’t show “no i2c device “ nor “i2c device found “.

This is how it was before re soldiering

Before picture shows them widely separated - so did you mount them together on a PCB? After that it didn't work?

Then you need to show an image of the back of the board, and show us a wiring diagram.

Nobody can guess what your soldering iron did.

Why not use a single oled with a larger screen, like those 1.3" ones? Then you would not need the multiplexer.

Yes they were on pcb. Both then and now sda from oled 1 is connected to sda 7 on tca, scl oled 1 to scl 7, oled’s 2 sda and scl to 6 sda and scl on tca, and finally Vcc from both displays are connected to each other and to 5v, same with ground, but obviously it is connected to ground :wink:

Previously (on one pcb with Arduino ) everything worked . Now they are also on pcb, but they are connected to 1 m cable , which is connected to pcb with Arduino .

I had 2 spare 0.91 ones, so it was easier to me

Sounds like you are having a problem with the multiplexer, not the displays. Post a picture of the solder side of the board.

I have come to the same conclusion, but it would be strange, because earlier it was working, and I haven’t changed soldiering to the tca . Thick black cable on the photo is going to pcb with displays .

Just to verify, you did not make any changes to the code?

...or so you thought...

De-solder everything and start over. You need the practice, my friend! I can see more potential solder bridges than I can count.

Get some 22AWG solid core hookup wire for making connections on the board. Lay the wires on the component side of the board with only the stripped wire ends going through to the solder side.

Use a 1.0mm "bevel" bit on a low power or temp controlled iron and use 0.5mm flux-core solder.

No, I didn’t

I did not want to do this, but I think you are right that this is the best way. Thanks for your advice about wire. On that board I was using not solid core wire, and you are right that solid one would be better. There is just one more thing that puzzles me. The thing is, when I checked the connections with a multimeter, I didn't see anything connected that shouldn't be, so i don't thing that it is because of bridges

I managed to solve the problem. Source of the problem was that black cable you can see on 1st and 2nd photo. It has 6 wires inside 0,2mm wide each. They are to thin to handle two screens. Now I must find as thin as possible cable with 6 wires (or 3 cables with 2 wires each ), that can handle that . Thanks for all your support. :heart:

You need to be careful running I2C though a cable, there is a lot of capacitive coupling between the wires and I2C has a limit on how much capacitance it can handle. If you use telephone or network cable the wires are usually paired and twisted together, making the problem worse.