"Noisy" USB connection?

u063096
Posts: 22
Joined: Wed Feb 13, 2019 3:27 pm

"Noisy" USB connection?

Postby u063096 » Tue Apr 02, 2019 6:16 pm

I am experiencing a strange effect when the ESP32 is connected to the PC via USB. My device is receiving data via 433MHz, the receiver is connected to a GPIO with the RMT analyzing the signal. When the ESP32 is running standalone, powered via 5V, the reception is excellent. But as soon as I will connect the USB cable to the computer, the signal gets noisy and disturbed. I am using a shielded USB cable with a ferrite ring, so I would expect the cable is not transmitting much.

What else can be the cause?

ESP_Sprite
Posts: 3118
Joined: Thu Nov 26, 2015 4:08 am

Re: "Noisy" USB connection?

Postby ESP_Sprite » Wed Apr 03, 2019 4:36 am

Maybe some kind of ground loop? Are you also powering the ESP32 from the 5V power supply when you plug it into USB?

u063096
Posts: 22
Joined: Wed Feb 13, 2019 3:27 pm

Re: "Noisy" USB connection?

Postby u063096 » Wed Apr 03, 2019 9:26 am

Yes, the 5V supply stays connected all the time. All grounds on the main board are connected - is there a separate loop perhaps on the DevkitC board acting as an antenna?

u063096
Posts: 22
Joined: Wed Feb 13, 2019 3:27 pm

Re: "Noisy" USB connection?

Postby u063096 » Thu Apr 04, 2019 8:09 am

Things get odder and odder...
I did several things to improve the supply trains - put in capacitors between 3.3v and GND, added a second GND connection to the DevkitC board, removed socket connections and soldered the modules directly to the board etc. Nothing changed the behaviour much, but when I apply my multimeter probes to measure the 3.3V supply, out of a sudden it works. I then thoroughly checked all solder joints to find a weak one, but to no avail.
The 5V supply is able to deliver up to 2A, so that should not cause 3.3V dropouts. The ESP32 brownout detection never struck, by the way, although active.
One thing I could imagine is the 433MHz receiver gets influenced by the metal mass of the probe wires (and the USB cable, of cause), but that would be difficult to find I am afraid.

u063096
Posts: 22
Joined: Wed Feb 13, 2019 3:27 pm

Re: "Noisy" USB connection?

Postby u063096 » Thu Apr 04, 2019 10:41 am

Another development: receiving 433MHz signals has completely ceased working now. The RMT reports status 0 - all fine -, but no signals are seen anymore.

To sort out faulty components, I used different receiver modules, different GPIOs to connect and even moved the receiver to the 5V train with a level shifter in between the receiver and the ESP32.

The last thing I had added was a Nextion display, powered by 5V as well and talking over the said level shifter with a HardwareSerial configured to GPIO16 and GPIO17, using UART2. The display is up and running and the ESP is talking to it, so I reckon it could not be the cause.

WTF could be happening here?

papaluna
Posts: 50
Joined: Tue Jan 30, 2018 11:27 am

Re: "Noisy" USB connection?

Postby papaluna » Thu Apr 04, 2019 12:20 pm

"There are three mutually exclusive ways to provide power to the board (DevKitC & Pico-Kit):
+ Micro USB port, default power supply
+ 5V / GND header pins
+ 3V3 / GND header pins

The power supply must be provided using one and only one of the options above, otherwise the board and/or the power supply source can be damaged."

https://docs.espressif.com/projects/esp ... ly-options
--
Paul.

u063096
Posts: 22
Joined: Wed Feb 13, 2019 3:27 pm

Re: "Noisy" USB connection?

Postby u063096 » Thu Apr 04, 2019 12:36 pm

Ough! Missed that bit!

I thought that the ESP would do it like the Arduino boards and choose whatever power supply was most stable.

Unfortunately even with just one power supply connected the issue is prevailing. In the meantime I found a receiver module that at least is generating data, but the sought signal is not to be found still. I may have blown the others, although I would not know how. Argh.

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