Emulates the DCF77 time signal on the RFID antenna and on GPIO A4 pin.
Uses PWM with frequency of 77.5 kHz on the GPIO pin to simulate the signal.
Normally the clock gets syncrhonized in two to five minutes depending on the signal strength.
The OK button changes the transmitted signal between CET and CEST (dst) time.
The RFID antenna wokrs best at distances of up to 50cm. The signal gets recognized in few seconds.
When using the GPIO, best results are achieved if you connect a ferrite antenna over 330 ohm resistor and a capactior to ground.
It also works with analog beeper or small in-ear headphone connected to the GPIO pin.