Noise when interacting with i2c

dynek=
Posts: 7
Joined: Thu Aug 27, 2020 11:28 am

Noise when interacting with i2c

Postby dynek= » Fri Mar 25, 2022 1:55 pm

Hello everyone,

I know this is super light, but before digging too much into it, I wanted to check if there's something obvious and known about ESP32 and i2c.

Got a GPIO (17) on an ESP32 wroom that is set to PWM 50% duty and here's what I see with the scope:
SDS00034.png
SDS00034.png (18.96 KiB) Viewed 4225 times
Now when there's an interaction on the i2c bus (RTC, ADC, LCD screen) here's what it becomes:
SDS00035.png
SDS00035.png (31.38 KiB) Viewed 4225 times
How can I get rid / lower that noise? I'm using GPIO 22 & 23 for i2c.

Any hint will be appreciated!

dynek=
Posts: 7
Joined: Thu Aug 27, 2020 11:28 am

Re: Noise when interacting with i2c

Postby dynek= » Sun Mar 27, 2022 9:36 pm

No one noticed this before? :|

ESP_Sprite
Posts: 9715
Joined: Thu Nov 26, 2015 4:08 am

Re: Noise when interacting with i2c

Postby ESP_Sprite » Mon Mar 28, 2022 1:06 am

It honestly looks like something caused by the way you measure things... it looks like the signal you get goes above Vcc and below Gnd, and the ESP32 is not capable of generating those voltages.

EDIT: No, I'm reading it wrong. Your original signal already is odd, as it has an amplitude of less than a volt and floats way above ground. Are you sure there isn't a break in your design somewhere and the signal is simply lightly capacitively coupling to your probe?

dynek=
Posts: 7
Joined: Thu Aug 27, 2020 11:28 am

Re: Noise when interacting with i2c

Postby dynek= » Mon Mar 28, 2022 6:29 am

It's A 2N3907 being driven high-side: https://www.eevblog.com/forum/beginners ... e-voltage/

ESP_Sprite
Posts: 9715
Joined: Thu Nov 26, 2015 4:08 am

Re: Noise when interacting with i2c

Postby ESP_Sprite » Mon Mar 28, 2022 8:14 am

If you're wondering if the ESP32 is generating that noise, better to measure it before the base resistor. (Also note that the noise seems to be pretty high-freq; making sure your oscilloscope ground doesn't make a big loop will probably also help to get an accurate measurement.)

andrea05256
Posts: 5
Joined: Mon Mar 21, 2022 5:29 am

Re: Noise when interacting with i2c

Postby andrea05256 » Mon Mar 28, 2022 9:47 pm

You should check the Grounds .... the whole circuit should have a common ground

and the circuit's ground should be common with the ground of the oscilloscope ....

dynek=
Posts: 7
Joined: Thu Aug 27, 2020 11:28 am

Re: Noise when interacting with i2c

Postby dynek= » Tue Mar 29, 2022 5:10 am

You are right, one of the ground cable was guilty for this, replaced it and it's ok now 👍👍

Thank you

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