FREE SIMULATOR EXAMPLE · BEGINNER

[Pico] Serial Echo

This example turns the Raspberry Pi Pico into a serial echo server: every character you type in the Serial Monitor is sent back with an Echo: prefix, and a heartbeat line prints every two seconds so you know the board is alive. It is the fastest way to verify the USB serial link between your computer and the RP2040.

Board	Raspberry Pi Pico (RP2040 dual-core Cortex-M0+, 133 MHz)
Difficulty	beginner
Category	communication
Libraries	None — just the Arduino core
Runs in	Sensbench browser simulator — free, no account

The exact circuit you get when you open this example — already wired, ready to run.

The sketch

// Raspberry Pi Pico — Serial Echo Test
// Echoes received characters and prints a heartbeat every 2 seconds

void setup() {
  Serial.begin(115200);
  delay(500);
  Serial.println("=== Pico Serial Echo ===");
  Serial.println("Type something and press Enter.");
  Serial.println();
}

unsigned long lastHeartbeat = 0;

void loop() {
  // Echo any incoming characters
  while (Serial.available()) {
    char c = Serial.read();
    Serial.print("Echo: ");
    Serial.println(c);
  }

  // Heartbeat every 2 seconds
  if (millis() - lastHeartbeat >= 2000) {
    lastHeartbeat = millis();
    Serial.print("[Heartbeat] Uptime: ");
    Serial.print(millis() / 1000);
    Serial.println("s");
  }
}

How it works

Every pass through loop() checks Serial.available() — if there is a byte waiting, it reads it and prints it back with an Echo: prefix. The RP2040’s USB CDC serial is fast enough that single-character echo feels instant even at 115200 baud.

The heartbeat uses millis() to track a two-second interval without blocking. This is the non-blocking pattern you want to learn early: the loop runs hundreds of thousands of times per second, but the heartbeat only fires when the timer expires. The uptime counter in seconds gives you a rough clock — useful for spotting resets or brownouts.

Before you build it for real

Related examples

FAQ

Why does it echo single characters instead of whole lines?

The sketch reads one byte at a time with Serial.read() and echoes immediately. If you want line-buffered input, collect characters into a buffer until you see \n, then echo the whole line. The single-char approach keeps the code minimal and proves the UART path works end-to-end.

What does the heartbeat tell me?

The heartbeat prints every two seconds whether you type anything or not. It confirms the Pico is still running and the USB serial link is alive — if the heartbeat stops but the board is still powered, the sketch has likely crashed or the USB cable has come loose.