Crash on connecting second I2C module

RE: Crash on connecting second I2C module

Aurabindo — Mon, 29 Jan 2018 16:08:11 GMT

Looks like it is, but after some rewiring, I'm getting the same problem again. But I'll mark this solved since the cause was found, and I could solve it.

RE: Crash on connecting second I2C module

MartinBL — Mon, 29 Jan 2018 15:21:16 GMT

So problem solved? Was it just due to crosstalk between SDA and SCL?

RE: Crash on connecting second I2C module

Aurabindo — Mon, 29 Jan 2018 14:26:20 GMT

@martinbl I was using slower sampling rate earlier. So it is possible that shorting the traces did not contribute to observation. I just got success communication to both of them together, after splitting the jumper wire that was connecting SDA & SCL. I think I really need to get them all on to a custom board!

RE: Crash on connecting second I2C module

MartinBL — Mon, 29 Jan 2018 08:59:52 GMT

I suppose a lot of wires would rather introduce a lot of extra capacitance and slow down rise and fall times, not introduce weird spikes. Is it possible to increase the sample rate of your logic analyzer? I can see there are small bumps in the signal below the spikes, but I think it is weird that it registers as a logic 1. It is also really weird that the spikes jumped from the data to the clock signal when you shorted the solder bridge. What I2C addresses are you using? And what device ID does your flash chip return?

RE: Crash on connecting second I2C module

Aurabindo — Sat, 27 Jan 2018 16:25:31 GMT

So its on rising edge of data that I get this spike on clk, and the I2C interprets this transaction as an ACK for a write to 0xEC, as per the logic analyzer. What would the cause for this interference? I'm using a breadboard,so there are quite a lot of wires running around. I also notice that my flash chip connected to the system is giving wrong device ID values. Its definitely interference. But how to figure out what exactly is the problem ?

RE: Crash on connecting second I2C module

Aurabindo — Sat, 27 Jan 2018 16:21:22 GMT

@martinbl I got a clue whats going wrong. I shorted the solderbridge as you suggested, and looked into the bus. I am (EDIT: not to now) now consistently getting the spikes in CLK line:

RE: Crash on connecting second I2C module

MartinBL — Thu, 25 Jan 2018 13:05:36 GMT

There is a picture of a schematic for you MPU9250 module in your link. It shows that there is a 3.3V voltage regulator between Vin and the MPU. There is likely a voltage drop across that regulator that could make life difficult for the MPU. I suggest that you short the solder bridge next to the regulator to bypass the regulator and make sure that power the MPU directly from Vin.

These two spikes are quite weird though. Do you know where they come from?

Are you using your own code? Have you tried a simple example to test basic functionality?