Using Leonardo as USB 2 UART bridger for uploading sketch to ESP32-Cam

[gojshlomo]

Hi All
I am a bloody beginner to micro controller programming and have an issue with the following project: I would like to use a Leonardo board as USB to UART bridge to program an ESP32-Cam board. In order for this I have tried using the following code, which is based on "USB/UART bride for Arduino Leonardo", written by Uli Koehler:

/*
  USB/UART bride for Arduino Leonardo
  Originally written by Uli Koehler in 2015
  Published on techoverflow.net

  Revision 1.0

  Published under the public domain (CC 1.0 Universal)
 */

void setup() {
  // Adjust baudrate here
  Serial.begin(115200);
  Serial1.begin(115200);
  //Wait until USB CDC port connects
  while (!Serial) {
  }
  Serial.write("USB-UART bridge ready.\r\n");
}

void loop() {
  //Copy byte incoming via TTL serial
  if (Serial1.available() > 0) {
    Serial.write(Serial1.read());
  }
  //Copy byte incoming via CDC serial
  if (Serial.available() > 0) {
    Serial1.write(Serial.read());
  }
}

I have successfully uploaded the sketch to the Leonardo board using port "COM4 (Arduino Leonardo)" and connected the Leonardo board to the ESP32-Cam board using the following schema:

Leonardo / ESP32-Cam

GND --> GND
5V --> 5V
TX --> voltage divider (1KΩ/2,2KΩ) --> U0RXD
RX --> 1KΩ --> U0TXD

On the ESP32-Cam board I have set a jumper for boot mode (GND --> GPIO0).

Now I would like to upload the following "Blink Example" sketch to the ESP32-Cam:

void setup() {
pinMode(flash, OUTPUT);
}

void loop() {
  digitalWrite(flash, HIGH);
  delay(1000);
  digitalWrite(flash, LOW);
  delay(1000);
}

When trying to upload the sketch using port COM4 the RX-LED on the Leonardo flashes once, but the Arduino EDI reports:
A serial exception error occurred: Write timeout
Note: This error originates from pySerial. It is likely not a problem with esptool, but with the hardware connection or drivers.
For troubleshooting steps visit: Troubleshooting - ESP32 - — esptool.py latest documentation
Failed uploading: uploading error: exit status 1

Have I made anything wrong?
How can the Leonardo board know whether I want to upload a sketch to the Leonardo board or send the data to the UART interface (ultimately to the ESP32-Cam)?

In Arduino EDI "Blink Example" project the target board is set to "AI Thinker ESP32-CAM". I have also tried "Upload Using Programmer", without success.

Any help would be greatly appreciated.

Edit:
I am now receiving a different error message when trying to upload the ESP32-Cam code:
Sketch uses 302166 bytes (9%) of program storage space. Maximum is 3145728 bytes.
Global variables use 20576 bytes (6%) of dynamic memory, leaving 307104 bytes for local variables. Maximum is 327680 bytes.
esptool.py v4.8.1
Serial port COM4
Connecting......................................

A fatal error occurred: Failed to connect to ESP32: No serial data received.
For troubleshooting steps visit: Troubleshooting - ESP32 - — esptool.py latest documentation
Failed uploading: uploading error: exit status 2

[blh64]

If you check out this video: https://www.youtube.com/watch?v=q-KIpFIbRMk

They have the TX/RX connected straight through but there is no code running on the Uno (not a Leonardo)

[gojshlomo]

Thanks, but I do not have a UNO at hand. Guess I will be purchasing a USB 2 UART converter, next time I will be placing an order.

But for now, I would like to understand what is going on. I have the impression that the ESP32-Cam sketch is not passed through to the ESP32-Cam, but uploaded to the Leonardo.

[alto777]

This one costs more than when I bought it years ago, but it is very flexible:

FTDI Friend

a7

[gojshlomo]

Thanks for the recommendation, but I still want to learn what is going on.

[alto777]

I too will be interested to see this run to ground.

a7

[blh64]

@gojshlomo

Thanks, but I do not have a UNO at hand.

You don't need an Uno. The idea works for the Leonardo as well. I was pointing out the idea of the RX/TX connection is swapped and there is no software running during an upload.