DCF77 transmitter for Raspberry Pi Pico W

Overview

This project is DCF77 transmitter for Raspberry Pi Pico W in proximate usage

This project supports:

• fetch CET (CEST) time by NTP
• DCF77 carrier frequency at 77500 Hz
• DCF77 amplitude modulation (High: 100%, Low: 12.5%)
• DCF77 phase modulation (0°, +15.6°, -15.6°) (Implemented, not verified yet)
• minimum peripheral circuits with wired headphones to emit weak radio waves

Supported Board

• Raspberry Pi Pico W

Pin Assignment

Pico Pin #	Pin Name	Function	Note
4	GP2	PIN_MOD_P	DCF77 signal differential output Pch
5	GP3	PIN_MOD_N	DCF77 signal differential output Nch

• Single-ended signal is not available since pair signals are asymmetrically driven in actual to have effect of PWM. Use a transformer to convert into single-ended output.

Connection Diagram

How to make the program work

• Use Thonny (Confirmed with Thonny 4.0.2, Python 3.10.9)
• Install MicroPython (Raspberry Pi Pico) interpreter firmware on Raspberry Pi Pico W by Thonny
• Confirmed with MicroPython v1.22.2
• Add secrets.py to include your WiFi configuration and put it on the storage of Raspberry Pi Pico W

# secrets.py
secrets = {
  'ssid': 'xxxx',
  'password': 'xxxx',
}

• Excecute pico_dcf77_tx.py from Thonny
• For stand-alone application, please rename pico_dcf77_tx.py as main.py and store in the storage of Raspberry Pi Pico W

Log

Bit description log displayed in the console is made compliant to https://www.dcf77logs.de/live except for Civil warning bits / weather information

Timecode: Sat, Jun 03, 2023 21:17:00  0-000000000000000-001001-11101000-1000010-110000-011-01100-110001001

Tips for emitting DCF77

• The recommended way to make the clock detect DCF77 emulated singal in limited proximate environment, is just to connect wired earphone between PIN_MOD_P and PIN_MOD_N pins through designated circuit (LPF) and put the clock close to the earphone cable. (This could damage the earphone. please try with cheaper one.)