A lightweight and reliable DCF77 time signal receiver library for ESP32, powered by FreeRTOS.
The decoder runs in a dedicated background task, providing precise time synchronization events without blocking other system operations.

• Runs DCF77 decoding in its own FreeRTOS task
• Non-blocking, thread-safe event handling
• Robust signal classification and noise filtering
• Automatic error detection and frame validation
• Real-time receiver status reporting (no signal / signal / synced)
• Works seamlessly alongside GPS or NTP synchronization
• Designed for long-term high-stability clock systems

• ESP32 board (tested on ESP32 DevKit and D1 Mini ESP32)
• Arduino Core for ESP32 v2.0+
• FreeRTOS (built into the ESP32 Arduino core)

#include <DCF77FreeRTOS.h>

DCF77FreeRTOS dcf(4);   // DCF input pin = 4

void setup() {
  Serial.begin(115200);
  dcf.begin(2);         // optional LED pin = 2
}

void loop() {
  DCFtime t;
  if (dcf.getTime(&t)) {
    Serial.printf("DCF time: %02d-%02d-%02d %02d:%02d (dow=%d)\n",
                  t.year, t.month, t.day, t.hour, t.minute, t.dow);
  }
  delay(1000);
}

The current receiver status can be retrieved using the getStatus() method.
Each state automatically times out to a lower level if no valid signal is received.

The receiver logic is fully interrupt-driven. Pulse lengths are measured from edge to edge with dead-time based noise suppression. Each impulse is classified by its duration and interpreted as a received bit. Valid DCF77 frames are decoded once per minute at the end of the 59-bit frame. Synchronization events are broadcast via FreeRTOS event groups. Several integrity checks ensure that only valid time data is reported.

This design allows for precise and efficient time decoding without blocking other tasks on the ESP32.

🪪 License

MIT License Copyright © 2025 Zoltán Szilvásy