DCF77 with Arduino ATMEGA 328, ATTINY85 and DCF-2 module from ELV

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This page describes the problems I ran into when programming the DCF with an ATMEGA 328 and a ATTINY85 processor.

The DCF77 library from Thijs Elenbaas can be used to get time from a DCF receiver using the ATMEGA interrupt OnRisingFlank.
When there are many spikes in the DCF-signal caused when the reception disturbed by external sources like LEDs or processors an other method may give better results. 
I have written a subroutine that averages the +20000 positive and negative signals received per second.
Combining the two methods improves the date/time calculation significantly when reception is not optimal.
I did not try it yet but it can be used with the ATTINY85 instead of the interrupt driven library but in the software of my DCF77-transceiver clock.


The DCF-module is from ELV elektronik AG. The DCF-2.
The module operates from 1.2 - 15V, gives a pulse between 0 and 5V and therefor easy to connect in the Arduino environment.

The DCF77 library is part of the Arduino software IDE and with the examples it is easy to start.
Unfortunately not all is as easy as one would like it to be. Especially if the system is not working. 

Produktabbildung DCF-Empfangsmodul DCF-2
This DCF-2 module gives a reversed signal what results is that 0 bits becomes a 1 and 1 bits zero in the software.
The blue line is what is measured direct from the DCF77 module (no signal at 5V and a pulse at 0V) and the yellow line what it should be (0V signal with a pulse of 5V).
To get this inversed (yellow) signal a inverter was made with a PNP-transistor BC327.
The 4.7K resistor is for pulling down the signal.
The 2.2K resistor is for safety. With out the resistor the circuit also operates.
The 100 nF ceramic capacitor is added for a smoother signal.
A BC556 transistor also works well.

But as I found out later the software has an option to use inverted signals.

The library initialization contains a third parameter; OnRisingFlank.
This is default set to true (HIGH).
Initialize the library as follows:

Below are the functions the library gives you to use:

                                                        //Initialize library
time_t getTime();     // Returns the current time in CET
time_t getUTCTime();  // Returns the current time in UTC
Start();              // Start listening to DCF77 signal
Stop();               // Stop listening to DCF77 signal

Nice links with info about DCF receivers:
Online signal from Mainflingen on website
Explains the bits in the received string Arduino projects 4you
HKW-Elektronik GmbH  Sells all kinds of receivers
Rheinturmfunkuhr mit Arduino
Arduino DCF77 radio clock receiver ,Matthias Dalheimer
Github Thijs Elenbaas
Conrad receiver

To use the ATTINY85 program must be uploaded with a Clock speed of16MHz processor.
The signal wire must be must be attached to Pin3 and the interrupt must be set to 0 in the program algorithm.
Detecting Rising flank interrupt 0 seems only be possible on pin3 was a suggestion in a forum.
A processor running at 16MHZ seems essential without changing the library timings.

Because the ATTINY85 does not have a serial.print I used the heartbeat subroutine to indicated that a time has been received.
Until the program received a proper decoded date/time it shows the DCF77 signal that is received.
The signal should be steady, turning on and off every second.
If not turn de rod and keep it horizontal. Step back a meter and let it start receiving.

Keep in mind nearby processors, magnetrons and bad power supplies disturbs the received signal.
A bad power supply set me back for weeks. Even a bad power supply in the same power supply socket disturbs a signal.

The INO source file


Upload parameters

// Version 04. Ed Nieuwenhuys 7 may 2017
// ATtiny45 / ATtiny85
//                        |----U----|
//            Pin 5 Reset | 1 o   8 | VCC
// (Analog input 3) Pin 3 | 2     7 | Pin 2 (Analog Input 1, SCK)
// (Analog input 2) Pin 4 | 3     6 | Pin 1 (PWM, MISO)
//                   -GND | 4     5 | Pin 0 (PWM, AREF, MOSI)
//                        |---------|

#include "DCF77.h"
#include "TimeLib.h"
enum PinAssignments
 PIN01 = 0,
 DCF_LEDP1 = 1,
 DCF LedPin PIN02 = 2,
 DCF_PIN = 3,          // DCF Pulse on interrupt pin
 PIN04 = 4,
 PIN05 = 5,

static unsigned long msTick; // the number of millisecond ticks since we last incremented the second counter

//-------------------------------------------- // Heartbeat //--------------------------------------------
uint8_t hbval = 128;
int8_t hbdelta = 8;
static unsigned long last_time = 0;
time_t time;
byte Heartbeat = 0;

#define DCF_INTERRUPT 0 // Interrupt number associated with pin
byte DCF_signal = 0; // is a proper time received?

void setup()
 pinMode(DCF_LEDP1, OUTPUT );
 analogWrite(DCF_LEDP1, 5);
 msTick = millis();

void loop()
 time_t DCFtime = DCF.getTime(); // Check if new DCF77 time is available
 if (DCFtime!=0)
   Heartbeat = 1;
 if (Heartbeat) heartbeat();
 else digitalWrite(DCF_LEDP1,1-digitalRead(DCF_PIN)); //Turn on/off the led

void heartbeat()
 unsigned long now = millis();
 if ((now - last_time) < 40) return;
 last_time = now;
 if (hbval > 230 || hbval < 20 ) hbdelta = -hbdelta;
 hbval += hbdelta;
 analogWrite(DCF_LEDP1, hbval);


Ed Nieuwenhuys, 26 februari 2021
November 2020, May 2017, September 2016
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