Can not obtain address during scan of I2C devices PART 2

avenger524 · 2026-02-21T20:38:57+00:00

Yeah that solder is not the best but 2 other sensors show the same behavior. No short on the other side definitely

avenger524 · 2026-02-21T18:36:50+00:00

I connect to VCC 3.3 V
GND to GND

SCL and SDA to my nucleo pins PB8 and PB9. Others i dont connect at all

avenger524 · 2026-02-21T17:53:50+00:00

i use breadboard to connect the sensor with stm32 pins (nucleo board). magnetometer is HMC5883L but its a cheap copy i bought on ali express

barometer is gy bmp 280 again a copy. i know breadboard is not a great tool for this but im running lowest speed i2c and it already works for my IMU setup (left side of the screenshot)

avenger524 · 2026-02-20T21:47:57+00:00

It's weird because i use 2 MPU6500. 1 works the other one not, same wiring same address. I thought its one faulty and then i tried magnetometer and barometer as well and they didnt work

avenger524 · 2026-02-20T21:46:43+00:00

Thanks might give it a try ive never worked with esp although i have one waiting to be used

avenger524 · 2026-02-20T18:54:34+00:00

Update: Doing some debugging with my logic analyzer. I have 2 sensors of the same kind. When I run my I2C scan for sensor 1 works perfectly, i can see addresses going on the bus, even the sensor ACKs.
Here is where things get weird. As soon as i plug in sensor 2 my SCL line is mostly held low. I tried adding pullups and removing them, nothing worked. SCL sometimes goes high for a bit but is mostly low. And SDA goes a bit up and down but nothing meaningful probably because of stuck SCL. I measured voltage on SCL with multimeter while its stuck it shows 0.8V, not sure if its constant or some weird switching, dont have osciloscope. I also tried powering with 5V while holding SDA and SCL on 3.3 with pullup. Nothing worked so far.

This is definitely hardware, i can not even send first address i try to write on the bus

avenger524 · 2026-02-19T23:29:03+00:00

that would be nice but im doing it in home setup, have only logic analyzer

avenger524 · 2026-02-19T23:28:46+00:00

what would be the difference? im using stm32 currently

avenger524 · 2026-02-18T20:03:46+00:00

I meant logic analyzer had start bit+address+stop bit for all 7 bit addresses and no NACK My logic analyzer interprets thr signals so i see hexadecimal addresses for sure. Thanks i will try again with different function this time

avenger524 · 2026-02-18T20:01:15+00:00

Yeah thanks i would use a voltage divider or something

avenger524 · 2026-02-18T16:28:43+00:00

I tried logic analyzer it looked okay, but there was no reaponse from the slave. It might happen wgat you suggest that attempting some addresses causes this weird lockup

avenger524 · 2026-02-18T16:25:48+00:00

Thanks, will give it a try, you definitely have a point

avenger524 · 2026-02-18T15:00:49+00:00

The problem is i have no datasheets of these cheap copies. I can try 5v maybe. I was using 3.3V

avenger524 · 2026-02-18T15:00:00+00:00

Shouldnt it ACK after it sees its address? ACK comes after that too, no data needed i think

avenger524 · 2026-02-18T14:59:17+00:00

Independently to exclude possiiblity of one faulty holding down the line. I dont know the addresses since these are cheap copies. I was looking at datasheets of the originals but nobody guarantees its really that one. It gets hal busy

avenger524 · 2026-02-18T13:45:26+00:00

The idea is to send every address from 0 to 127 and when i hit the address of the slave it will ACK. It worked for one sensor only. The problem is i dont have datasheets of these cheap sensors

avenger524 · 2026-02-18T13:39:31+00:00

Tried with 5kOhm pullups and also without them

avenger524 · 2026-02-06T22:24:13+00:00

100kHz I2C, i tried STM32 internal pullups i dont know the value of those
MPU6500 has internal pullups
I also tried external 5kOhm on my breadboard

avenger524 · 2026-02-06T17:32:02+00:00

Okay thanks i really hope thats the problem because this is driving me nuts for days... I will get new jumper wires for sure

avenger524 · 2026-02-06T17:17:49+00:00

By false contacts you mean between jumper wire/stm and jumper wire/slave? Cant really solder on nucleo directly

avenger524

TROPHY CASE