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#1

A20 / Re: HDMI connection back feedi...

Last post by LubOlimex - Today at 08:21:27 AM

Measure to see if the issue exists without the serial debug cable. Maybe try another serial debug cable, we've had similar problems in the past with some serial debug cables that might power the board parasitically from the data line (RX and TX).

If not consider other ways to debug the board like SSH or mini USB, as detailed in the manual:

https://raw.githubusercontent.com/OLIMEX/OLINUXINO/master/DOCUMENTS/OLIMAGE/Olimage-guide.pdf

#2

A20 / Re: HDMI connection back feedi...

Last post by dry - March 05, 2026, 02:44:51 PM

https://olimex.wordpress.com/2014/01/22/bevare-non-grounded-tv-monitors-can-damage-your-olinuxino/

Oh, I just read your post in the link, and had Oh crap moment:
"We use cheap TV HDMI monitor to test OLinuXino boards, and we noticed that several OLinuXino boards got burned when connected to the TV monitor and USB-SERIAL-CABLE to the console. UART Tx signal got burned when TV is connected, so we decided to investigate further"

I just realized that I started with this issue check when I noticed that, for some odd reason, I had to un-plug my USB to serial converter dongle that's connected to those UART0 headers on the OLinuXino (only tx,rx,gnd, no 3v3), and re-boot, for ethernet troubleshooting. And then I noticed that HDMI backfeed.

So far I have not seems burned signals, I hope..

Should I start using USB-ISO..?

#3

A20 / Re: HDMI connection back feedi...

Last post by dry - March 05, 2026, 02:33:19 PM

Ye ok, don't want to overfocus on this but as I said, sometimes I have weird states like ethernet wont come up every time on boot, or .

I will try FUSE work around, and hope not to messup my olixino, thank you.

#4

A20 / Re: HDMI connection back feedi...

Last post by LubOlimex - March 05, 2026, 10:23:42 AM

Latest that we sell, I got it from the shop. Revision N it is. But this part of the circuit hasn't been changed like forever. It is something else, probably some option in the monitor or the monitor itself (HDMI CEC) or maybe the monitor is not properly grounded... Maybe try powering the monitor from another outlet that is properly grounded. But it can be an issue with the monitor itself. Some monitors are not grounded. We published this article 12 years ago:

https://olimex.wordpress.com/2014/01/22/bevare-non-grounded-tv-monitors-can-damage-your-olinuxino/

Maybe try the FUSE workaround.

#5

A20 / Re: HDMI connection back feedi...

Last post by dry - March 05, 2026, 02:23:01 AM

Interesting, I have another DELL model U2715H, and that behaves same, still read 1.8V.

Tested by connecting to HDMI port from 2 different Lenovo laptops - bad test probably? ...one from 2017 model one from 2025, both then give me full 5V on same pins (with olimex not powered through own power).

Connected to my 65" Sony OLED tv, to one of its HDMI, and that is only time I didn't seem to see any voltage on the Olimex board, but I cannot confirm that HDMI would have worked at all with Sony TV - as I didn't get any test that port would work woth Olimex.

By the way, my Olinuxino-Micro is Rev.M board, I bought it some years back. Which version you tested?

Thanks for support

#6

ESP32 / Re: ESP32-C6 power supply

Last post by LubOlimex - March 04, 2026, 04:45:36 PM

Thank you for the update! Glad you got it sorted!

#7

ESP32 / Re: ESP32-C6 power supply

Last post by Partec - March 04, 2026, 03:33:05 PM

Sorry, It was a software problem.
Troubleshooting - No Boot: If the ESP32-C6 refuses to run code without a serial terminal connected, remove any while(!Serial); lines from your setup() function, as this waits for a connection that may not exist.
Now is OK

#8

ESP32 / Re: ESP32-C6 power supply

Last post by Partec - March 04, 2026, 02:34:16 PM

I use Arduino IDE version 2.3.5
Very simple software rele 1 on/off every 4 seg. code:

//Prueba placa OLIMEX ESP32-C6-EVB

// ====== PINES ======
const int inputPins[4] = {1, 2, 3, 15};      // Entradas
const int relayPins[4] = {10, 11, 22, 23};    // Relés


void setup() {
  Serial.begin(115200);
  while(!Serial) delay(10);

  for(int i=0;i<4;i++){
    pinMode(inputPins,INPUT_PULLUP);
    pinMode(relayPins,OUTPUT);
    digitalWrite(relayPins,LOW);
  }
  Serial.println("Termino el setup");

}

void loop() {
  digitalWrite(relayPins

• ,HIGH);

  Serial.println("rele HIGH");
  delay(4000);
  digitalWrite(relayPins

• ,LOW);

  Serial.println("rele LOW");
  delay(4000);
}


If I power it with USB or with USB and 12V, everything is OK, it works, and if I press the reset button, it restarts without a problem.

If I power it only with 12V (12V 5A power supply):
A) It continues to work if it was previously powered by USB. (I disconnect the USB while the 12V is still applied)

B) If I press the reset button, it doesn't start and doesn't work again.

C) From a powered-off state, with no power supply, I connect the 12V, and it doesn't start.

#9

A20 / Re: HDMI connection back feedi...

Last post by LubOlimex - March 04, 2026, 11:11:22 AM

I checked today with few HDMI monitors and displays here and it doesn't happen here. They don't feed power to the board. It is some sort of problem with your specific monitor.

I also tested something else, if the HDMI output would work if I remove the power pin (pin 18) of the HDMI - good news is that it works. Sadly I can't tell if that would fix the issue since our displays don't provide parasitic power.

So if you have some soldering skills - maybe try the same unsolder and remove FUSE1 (it is just below the HDMI connector at the bottom) on the +5V line of the HDMI and test again. If it doesn't solve the issue, solder it back.

#10

ESP32 / Re: ESP32-C6 power supply

Last post by LubOlimex - March 04, 2026, 08:45:33 AM

Give us more details about the software. How do you determine that it doesn't boot? Did you try with very simple code?