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Built-in project · ESP32-C3-DevKitM-1

Blink, with a breakpoint, on an ESP32-C3

Stop the board on the line that lights the LED, and see it frozen mid-blink with its registers. The whole build, an ESP32-C3 and 2 more parts, 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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Teaching? Assign it to your class in one click.

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

The parts retail for about $13.15. On Mokxi they're free.

The circuit runs here once the page has loaded.

What you'll learn

  • Setting a breakpoint in the gutter
  • Pausing a running program on one line
  • Reading registers while stopped
  • Stepping one line at a time
  • Difficulty: Beginner
  • Time: About 10 minutes
  • Board: ESP32-C3-DevKitM-1
  • Parts: 4

How it works

An ESP32-C3 board drives a blue LED from pin 8 through a 220 ohm resistor, with the other leg of the LED on ground. The sketch turns the pin on for half a second, then off for half a second, over and over.

The point here is the debugger. Click the gutter beside the digitalWrite(LED_BUILTIN, HIGH) line to set a red dot, then press Run. The board stops on that line before it runs, with the clock frozen too. The Debug tab shows where it stopped, the registers and a watch list. Step over runs one line, and Continue lets it go.

Parts list

4 parts, plus the jumper wires. They retail for about $13.15; on Mokxi they're free.

Wiring table

Every connection, pin by pin, read from the circuit itself. Each row joins the pin on the left to the pin on the right, by a jumper wire or a breadboard strip.

Part and pinConnects to
LED, blue pin CESP32-C3-DevKitM-1 pin GND
Resistor, 220 Ω pin 1ESP32-C3-DevKitM-1 pin 8
LED, blue pin AResistor, 220 Ω pin 2

The note on the canvas

Word for word, as it sits beside the circuit in the editor.

Set a breakpoint

1. Press Run and watch the LED blink.
2. Click the gutter left of the line numbers, beside digitalWrite(LED_BUILTIN, HIGH). A red dot appears.
3. Press Run again. The board stops on that line, before it runs, and the LED stays exactly as lit as it was. So does everything else: the clock stops with it.
4. The Debug tab, beside the serial monitor, has where it stopped, the registers, and a watch list.
5. Step over runs one line. Continue lets it go.

A hollow dot means that line generated no instruction, so nothing can stop there.

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
// Blink: the smallest thing a board can do.
//
// GPIO 8 is the LED on the ESP32-C3-DevKitM-1, so LED_BUILTIN is 8. Wire an
// LED and a resistor from GPIO 8 to GND to see it on the breadboard too.

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

void loop() {
  digitalWrite(LED_BUILTIN, HIGH);
  delay(500);
  digitalWrite(LED_BUILTIN, LOW);
  delay(500);
}

Code walkthrough

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

setup sketch.ino

Runs once. It sets LED_BUILTIN as an output. On this board that is GPIO 8, the same pin your wired LED uses.

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

loop sketch.ino

Turns the LED on, waits 500 ms, turns it off, waits 500 ms. Put your breakpoint on the digitalWrite(LED_BUILTIN, HIGH) line and the board stops right before the LED lights.

void loop() {
  digitalWrite(LED_BUILTIN, HIGH);
  delay(500);
  digitalWrite(LED_BUILTIN, LOW);
  delay(500);
}

Troubleshooting

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

  • The breakpoint dot is hollow and never stops This project
    A hollow dot means that line made no instruction. Move it to a line with real code, like a digitalWrite.
  • The LED never lights This project
    Check the LED direction: the flat side (cathode) goes toward ground, and the resistor goes between pin 8 and the LED.
  • The LED is dim, burns out, or the pin reads wrong because the resistor value is off. Resistor
    Read the color bands again. A 220 ohm to 330 ohm resistor suits a typical LED on 5 V. 10k is a common pull-up or pull-down value. Check with a multimeter if unsure.
  • A pull-up or pull-down resistor is missing, so the input floats and reads random values. Resistor
    Tie the input to 5 V or ground through about 10k. Or use INPUT_PULLUP and wire the switch to ground.
  • The LED does not light, or it lights once and then dies. LED
    LEDs have polarity. The longer leg (anode) goes toward the positive side. Always add a series resistor, about 220 ohms to 1 k ohm on a 5 V pin.
  • A blue or white LED stays dark on 3.3 V. LED
    Blue and white LEDs drop about 3 V, so 3.3 V leaves almost nothing for the resistor. Use a 5 V supply, or a smaller resistor and a red or green LED.
  • 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.

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