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Built-in project · ESP32-C3-DevKitM-1

ESP32-C3 serial

The board on its own, printing its uptime once a second on UART0 and echoing anything typed into the serial monitor. The whole build, an ESP32-C3, runs here in your browser on the firmware below; open it in the editor to change the wiring or the code and run it again.

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Beginner About 10 minutes to build and run. Runs in your browser. Free, and no account needed.

The parts retail for about $13. On Mokxi they're free.

ESP32-C3 serial · ESP32-C3-DevKitM-1live0.000 s 0.00x
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The circuit itself, running here on the simulator. Press what can be pressed; click anything else to open it in the editor.

What you'll learn

  • Printing with Serial.println
  • Timing without blocking, using millis
  • Reading typed input with Serial.available
  • Showing a character as a hex code
  • Difficulty: Beginner
  • Time: About 10 minutes
  • Board: ESP32-C3-DevKitM-1
  • Parts: 2

How it works

This project is just the board, with no extra parts. It talks to you through the serial monitor on UART0. At start it prints a greeting and shows pi to five decimal places.

After that it reports its uptime in milliseconds once a second. It also listens: type something into the monitor and the board replies with each character and its hex code. A newline is shown as a word.

Parts list

2 parts, plus the jumper wires. They retail for about $13; on Mokxi they're free.

The code

The firmware exactly as the editor opens it. Change a line there and press Run: it compiles in the browser.

sketch.ino · ESP32-C3-DevKitM-1
// Serial: print once a second, echo what arrives.
//
// Serial is UART0, which is the board's channel to the serial monitor at the
// bottom of the window. Type into the monitor and the characters come back
// with a prefix.
//
// Serial.print blocks while the 128-byte transmit FIFO is full, so a long
// line costs simulated time at the configured baud rate, exactly as it would
// on the real board.

unsigned long lastReport = 0;

void setup() {
  Serial.begin(115200);
  Serial.println("Mokxi ESP32-C3: serial example");
  Serial.print("pi to five places is ");
  Serial.println(3.14159265, 5);
}

void loop() {
  unsigned long now = millis();
  if (now - lastReport >= 1000) {
    lastReport = now;
    Serial.print("up ");
    Serial.print(now);
    Serial.println(" ms");
  }

  while (Serial.available() > 0) {
    int c = Serial.read();
    if (c == '\r') {
      continue;
    }
    Serial.print("you typed: ");
    if (c == '\n') {
      Serial.println("<newline>");
    } else {
      Serial.print((char)c);
      Serial.print(" (0x");
      Serial.print(c, HEX);
      Serial.println(")");
    }
  }
}

Code walkthrough

The key functions of the sketch, and what each one does.

setup sketch.ino

Opens serial at 115200 baud, then prints a greeting and pi. The 3.14159265, 5 form tells println to show five decimal places.

void setup() {
  Serial.begin(115200);
  Serial.println("Mokxi ESP32-C3: serial example");
  Serial.print("pi to five places is ");
  Serial.println(3.14159265, 5);
}

loop sketch.ino

Does two jobs. First it compares millis() to lastReport, and once 1000 ms have passed it prints the uptime. Then a while loop reads every waiting byte with Serial.read, skips carriage returns, and prints each character with its hex value.

void loop() {
  unsigned long now = millis();
  if (now - lastReport >= 1000) {
    lastReport = now;
    Serial.print("up ");
    Serial.print(now);
    Serial.println(" ms");
  }

  while (Serial.available() > 0) {
    int c = Serial.read();
    if (c == '\r') {
      continue;
    }
    Serial.print("you typed: ");
    if (c == '\n') {
      Serial.println("<newline>");
    } else {
      Serial.print((char)c);
      Serial.print(" (0x");
      Serial.print(c, HEX);
      Serial.println(")");
    }
  }
}

Troubleshooting

The usual mistakes with this circuit, and the fix for each.

  • Garbled text in the serial monitor This project
    The monitor speed must match Serial.begin(115200).
  • Typed characters get no reply This project
    Send the text from the monitor's input box, and make sure the sketch is running.
  • Upload fails or the board is not found by the computer. ESP32-C3-DevKitM-1
    Pick the ESP32-C3 board in your tools and the right port. If it still fails, hold BOOT, tap RESET, then release BOOT to enter download mode and try again.
  • GPIO pins act strangely or the board resets. ESP32-C3-DevKitM-1
    GPIO is 3.3 V only, so never feed it 5 V. GPIO 18 and 19 are USB, and GPIO 2, 8 and 9 are boot strapping pins. Avoid loading them at reset.

Change it and keep it

Open it in the editor, change the circuit or the code, and keep your version in a free account.

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