TFT DCF77 Analyzer with TFT Serial Monitor & DCF77 Filter

This is a TFT version of Erik de Ruiter's DCF77 Analyzer Clock. The DCF77 signal including weather is decoded and displayed on a 2.8" ILI9341 TFT via a Lolin D32 Pro v2 board.

Coded by tobozo it also includes full weather data decode city by city.

I have added a serial monitor using an Atmega 328 with a 2nd TFT alongside the Analyzer TFT to show the weather decode live.

A modified Udo Klein DCF77 Super Filter is also added via a 2nd Atmega 328 to clean up very noisy signals.

The DCF77 Super Filter serial output can also be displayed on the Serial monitor if required.

Video

Typical DCF77 Analyzer outputs.

Features

DCF77 Signal Displayed on a 2.8" TFT Screen second by second

Decoded Weather Data is displayed on a 2nd TFT Screen

DCF77 Signal can be filtered/error corrected

DCF77 filter level can be set to low (filtered) or high (fully synthesized)

DCF77 filter info can be displayed on the 2nd TFT screen if required

Serial Monitor can be used to monitor external sources

Serial monitor baud rate can be set to 5 different values

A full minute of DCF77 Data being received

Credits

There are three distinct parts to this project.

DCF77 TFT Analyzer

TFT Serial Monitor

DCF77 Super Filter

All the parts can be built stand alone as required.

DCF77 TFT Analyzer  Copyright (c) 2018 tobozo

I had an initial version of the tobozo's DCF77 TFT Analyzer working on a TTGO TS v1.2.

This worked fine but I found the display too small.

I wanted to use a 320x240 2.2" or 2.8" TFT display and tobozo kindly provided me with some prototype code and helped me

get it working on a 2.8" 320x240 ILI9341 TFT display.

I have modified the prototype code in places to make it fit the larger display correctly.

The serial output to display the Meteo Data was designed for a full screen serial monitor so I have also modified this to fit on a 2.8" TFT display.

TFT Serial Monitor  by Alan Senior

The original sketch was included as an example in the Adafruit_ILI9341_AS library.

I have modified the code so the baud rate can be modified on startup.

Switches are included so the DCF77 decode, Super Filter or an external serial input can be displayed.

If switched to the external input with nothing connected this will pause the last serial input.

This is useful when viewing the Filter output as it changes once per second.

DCF77 Super Filter by Udo Klein

When switched on the Udo Klein's Super Filter actively processes the incoming DCF77 signal

from the antenna/receiver. After a few minutes of sampling the DCF77 signal the Super Filter will predict the DCF77 signal and use this

to determine if the incoming signal contains any errors. The Super Filter will then synthesize a corrected DCF77 signal even if the signal is absent.

I have modified the Super Filter Code to add extra monitor LEDs, there are now 10 in total.

In order to do this I have removed 4 modes from the filter just leaving synthesized and inverted synthesized.

Detailed DCF77 Signal and Filter  information (I have changed what's output and the format) can be viewed on the TFT Monitor

The DCF77 Signal

DCF77 is a German long wave time signal and is transmitted from Mainflingen Germany, about 25 km south-east of Frankfurt am Main.

The DCF77 signal is an amplitude-modulated, pulse-width coded 1 bit/s data signal. As each bit is transmitted every second it makes it a very visible time signal for displaying on the TFT display.

Map showing the distance from the DCF77 transmitter in Germany.

In Kenley UK we are able to get very good DCF77 reception. I monitor this 24/7 and show live charts see below so you can see if your signal interference is similar to mine.

Live charts showing DCF77 signal reception in Kenley UK

1 = all 60 bits of data received with no errors in the last minute. 0 = 1 or more data bits received in the last minute had an error.

DCF77 is controlled by the Physikalisch-Technische Bundesanstalt (PTB), Germany's national physics laboratory and transmits 24/7.

Most service interruptions are short-term disconnections of under two minutes. Longer lasting transmission service interruptions are generally caused by strong winds, freezing rain or snow induced T-antenna movement.

This manifests itself in electrical detuning of the antenna resonance circuit and hence a measurable phase modulation of the received signal. When the maladjustment is too large, the transmitter is taken out of service temporarily. Over a year this will typically be a few hours.

The time code sent is either in Coordinated Universal Time (UTC)+1 or UTC+2 depending on daylight saving time.

The time is represented in binary-coded decimal. It represents civil time, including summer time adjustments.

The time transmitted is the time of the following minute; e.g. during December 31 23:59, the transmitted time encodes January 1 00:00.

The chart below shows the makeup of the DCF77 time code transmitted at 1 pulse per second over 60 seconds

This chart shows details of the transmitted code

DCF77 Weather Data

 Encrypted weather data is transmitted, alongside the time and date information, from the DCF77 transmitter.

In each minute there are 14 bits which are sent and one weather message consists of three consecutive minutes of 14 bits of weather data. In total 42 bits are used.

Note bits 1 and 8 from the first minute are not used.

In addition there are 40 bits needed derived from the time signal itself, this acts as the cypher.

The 42 bits of data are collected from bits 1 to 14 over 3 minutes.

Serial monitor showing decoded weather info after 3 consecutive error free minute decodes.

There are 480 of these pages in a day making up the weather/forecast for the DCF77 area       

14 encrypted weather bits are transmitted every minutes making 42 bits in total

The transmission starts again after 24 hours at 10 p.m. UTC with region 0.

A total of 90 regions in Europe are supplied with weather data.

60 with a 4-day forecast and 30 with a two-day forecast. This results in the following sequence:

Start at 10 p.m. UTC with
region 0 - 59 maximum values ​​1st day (today)
region 0 - 59 minimum values 1st day (today)

region 0 - 59 maximum values ​​2nd day (tomorrow)
region 0 - 59 minimum values 2nd day (tomorrow)

region 0 - 59 maximum values ​​3rd day
region 0 - 59 minimum values 3rd day

region 0 - 59 maximum values ​​4th day
region 0 - 59 Weather anomalies and wind data for the 4th day.

Since no minimum values ​​are transmitted for the 4th day, one uses the capacities freed up for
region 60 - 89 maximum values ​​1st day
region 60 - 89 maximum values ​​2nd day

It should be noted that the data for two regions are transmitted in the last 60 data records transmitted.

Weather Code Times in London note shown in CET take an hour off for GMT

Regions

Region No.	Region/City	Region No.	Region/City	Region No.	Region/City	Region No.	Region/City	Region No.	Region/City	Region No.	Region/City
0	FRANCE  Bordeaux	15	BRITAIN Swansea	30	GERMANY  Erfurt	45	GERMANY  Strasbourg	60	ITALY  Napoli	75	IRELAND Galway
1	FRANCE  la Rochelle	16	BRITAIN Manchester	31	SWITZERLAND Lausanne	46	AUSTRIA  Klagenfurt	61	ITALY  Ancona	76	IRELAND Dublin
2	FRANCE  Paris	17	FRANCE  le Havre	32	SWITZERLAND Zuerich	47	AUSTRIA  Innsbruck	62	ITALY  Bari	77	BRITAIN Glasgow
3	FRANCE  Brest	18	BRITAIN London	33	SWITZERLAND Adelboden	48	AUSTRIA  Salzburg	63	HUNGARY  Budapest	78	NORWAY  Stavanger
4	FRANCE  Clermont	19	GERMANY  Bremerhaven	34	SWITZERLAND Sion	49	AUSTRIA  Wien	64	SPAIN Madrid	79	NORWAY Trondheim
5	FRANCE  Beziers	20	DENMARK Herning	35	SWITZERLAND Glarus	50	CZECH REPUBLIC Praha	65	SPAIN  Bilbao	80	SWEDEN  Sundsvall
6	BELGIUM  Bruxelles	21	DENMARK Arhus	36	SWITZERLAND Davos	51	CZECH REPUBLIC Decin	66	ITALY  Palermo	81	POLAND Gdansk
7	FRANCE  Dijon	22	GERMANY  Hannover	37	GERMANY  Kassel	52	GERMANY  Berlin	67	SPAIN  Palma	82	POLAND Warszawa
8	FRANCE  Marseille	23	DENMARK Copenhagen	38	SWITZERLAND Locarno	53	SWEDEN  Gothenburg	68	SPAIN  Valencia	83	POLAND Krakow
9	FRANCE  Lyon	24	GERMANY  Rostock	39	ITALY  Sestriere	54	SWEDEN  Stockholm	69	SPAIN  Barcelona	84	SWEDEN  Umea
10	FRANCE Grenoble	25	GERMANY  Ingolstadt	40	ITALY  Milano	55	SWEDEN  Kalmar	70	AN Andorra	85	SWEDEN  Oestersund
11	SWITZERLAND La Chaux	26	GERMANY  Muenchen	41	ITALY  Roma	56	SWEDEN  Joenkoeping	71	SPAIN  Sevilla	86	SWITZERLAND Samedan
12	GERMANY  Frankfurt/M	27	ITALY  Bolzano	42	NETHERLANDS Amsterdam	57	GERMANY  Donauechingen	72	SPAIN  Lissabon	87	CROATIA Zagreb
13	GERMANY  Trier	28	GERMANY  Nuernberg	43	ITALY  Genova	58	NORWAY  Oslo	73	ITALY  Sassari	88	SWITZERLAND Zermatt
14	GERMANY  Duisburg	29	GERMANY  Leipzig	44	ITALY  Venezia	59	GERMANY  Stuttgart	74	SPAIN  Gijon	89	CROATIA Split

Leap Second

A leap second is a one-second adjustment that is occasionally applied to Coordinated Universal Time (UTC), to accommodate the difference between precise time (as measured by atomic clocks) and imprecise observed solar time (known as UT1

and which varies due to irregularities and long-term slowdown in the Earth's rotation). The UTC time standard, widely used for international timekeeping and as the reference for civil time in most countries,

uses precise atomic time and consequently would run ahead of observed solar time unless it is reset to UT1 as needed.The leap second facility exists to provide this adjustment.



Because the Earth's rotation speed varies in response to climatic and geological events,UTC leap seconds are irregularly spaced and unpredictable. Insertion of each UTC leap second is usually decided about six months in advance by the International Earth Rotation and Reference Systems Service (IERS),

to ensure that the difference between the UTC and UT1 readings will never exceed 0.9 seconds.

Insertion of Leap Seconds

The scheduling of leap seconds was initially delegated to the Bureau International de l'Heure (BIH), but passed to the International Earth Rotation and Reference Systems Service (IERS) on January 1, 1988. IERS usually decides to apply a leap second whenever

the difference between UTC and UT1 approaches 0.6 s,in order to keep the difference between UTC and UT1 from exceeding 0.9 s.

The UTC standard allows leap seconds to be applied at the end of any UTC month, with first preference to June and December and second preference to March and September. As of January 2017, all of them have been inserted at the end of either June 30 or December 31.

IERS publishes announcements every six months, whether leap seconds are to occur or not, in its "Bulletin C". Such announcements are typically published well in advance of each possible leap second date – usually in early January for June 30 and in early July for December 31.

Some time signal broadcasts give voice announcements of an impending leap second.



Leap Seconds since 1972

Between 1972 and 2020, a leap second has been inserted about every 21 months, on average.

However, the spacing is quite irregular and apparently increasing: there were no leap seconds in the six-year interval between January 1, 1999 and December 31, 2004,but there were nine leap seconds in the eight years 1972–1979.

Unlike leap days, which begin after February 28 23:59:59 local time,[a] UTC leap seconds occur simultaneously worldwide; for example, the leap second on December 31, 2005 23:59:60 UTC was December 31, 2005 18:59:60 (6:59:60 p.m.) in U.S. Eastern Standard Time and January 1 and January 1 00:59:60 CET Central European Time.
 

WIKIPEDIA

DCF77 Leap Second
The Leap Second is announced in the DCF77 signal 1 hour before the leap second is due. This is signaled by Bit 19 of the DCF77 signal being set to 1 an hour before the leap second.

Therefore DCF77 clocks will receive 60 of these before the leap second bit is sent.

The leap second bit (always 0) is sent on the 60th bit and is followed by the normal minute marker.

This means that minute will last for 61 seconds rather than 60.

Below looped animation -leap second being received on my DCF77 Analyzer

The inner ring shows the incoming DCF77 signal in real time (Grey is 0 and Red is 1).

The inner ring shows the DCF77 buffer and is labeled 0 to 59 for the 60 seconds of the minute being received.

Normally buffer 59 is blank as per the corresponding mark on the outer ring for the last minute. A leap second is inserted here shown by an extra 0 on buffer 59.

The time is the time on the RTC and this resets itself as normal to 01:00:00 after 59 seconds but the buffer store inner ring is not reset nor is the current time buffer store updated.

The Analyzer picks up the extra leap second bit then resets the whole buffer store and updates the current buffer outer ring with the new time and resets the RTC to 01:00:00 again 1 second later.

The RTC is now 1 second slower after the insertion of the Leap Second

This image shows the leap second as an extra 0 bit on the inner ring buffer store.

The RTC has reset to 01:00:00.

"Leap Second Inserted" warning appears below the time.

The time & date of the last leap second is displayed on the TFT.

Looped animation showing the leap second detail and how it makes the DCF77 controlled clock lose 1 second.

Main TFT Analyzer Control Panel

The control panel is split into four sections DCF77 ESP32 Analyzer,  DCF77 Filter, Power/Display & Serial Monitor

The DCF77 ESP32 Analyzer contains the main TFT display showing the DCF77 signal and decoding.

The DCF77 Filter contains the filter LEDs and filter control switches.

The Power/Display section has common controls for main power and TFT display backlights On or Off.

The Serial Monitor Section contains the serial TFT display and control switches for the serial monitor.

DCF77 TFT Analyzer Detail  tobozo

Modelled on Eric The DCF77 analyzer works on a  ILI9341 TFT via a Lolin D32 Pro v2 board.

It seems to work on all 2.2" ILI9341 TFT displays but for some reason only works on 2.8"  ILI9341 touch displays.

tobozo has created a branch off the main esp-DCF32_Analyzer_Clock on github for this version.

Emulating Erik de Ruiter's DCF77 Analyzer Clock the analyzer displays the DCF77 time code on 2 rings of 60 "LEDs" on the TFT display.

The inner ring shows the live time code for the next minute as it is received

and the outer ring shows the current time as long as the previous minute was received error free.

Decoded time and date in UTC + 1 or UTC + 2 are shown in the middle of the "LED" rings along with the chosen City and forecast for that city.

Note I have not added adjustments for GMT my home location as I don't use this as a clock just an analyzer.

The animation below shows a full minute of data capture and decode.

The top right of the screen is used to display DCF77 pulse timings and bit information along with the buffer number and number of errors.

The bottom right of the TFT shows the week number, leap year, CET/CEST and also the day of the week.

Top left has DCF77 status indications that change colour depending on their state-Green for good grey no status and red for bad.

There are indicators for DCF77 sync, Minute mark, RTC, Buffer Full, Buffer Overflow, Pulse width error and period of time error.

The bottom left of the display shows the parity for Minutes, Hour and Date in 3 colours.

These are Grey-waiting parity check, Green-parity check OK & Red parity check fail.

Note the very bottom left of the display is not in use and will probably be used for Meteo data info in the future.

The full TFT display on a 2.8" TFT

The illustrations below give further details on the displays

As per the Erik's original analyzer there is an option to do an (LED) test on boot.

Not really necessary on a TFT but a nice touch anyway.

Animation showing the DCF77 Analyzer Boot-up Screen

DCF77 Initial Sync

On boot the time and date are fetched from the RTC.

If this is the first boot the time and date will no be correct as the RTC is set once a complete DCF77 signal is received and decoded.

After this if the analyzer is powered down the RTC stores the time and date.

This animation shows the clock receiving it's initial sync.

The buffers are initial empty and after the analyzer detects a minute mark the received data is loaded into the inner ring once per second.

If no pulse timing or parity errors are found the data is loaded into the outer ring and decoded updating the RTC and filling out the missing data on the display.

The inner ring is emptied ready for the next minutes worth of data.

Note weather data will not be loaded until the weather information for your chosen city is received.

This information of each city  is sent over 3 minutes worth of data at various times of the day.

See the DCF77 weather section above for full details.

DCF77 Meteo Data display

Unlike Erik's analyzer tobozo has included full DCF77 weather decoding in his version.

The weather information for your chosen city is displayed on the analyzers TFT screen.

The full weather decode is sent out over the serial port and can be displayed on a serial monitor.

My analyzer has a built in TFT serial monitor display.

Unlike the Arduino serial monitor my TFT monitor is limited in the information it can display.

I have modified the serial printing so all the data for each city  fits onto my TFT display.

The data for each city is received over three consecutive minutes in 14 bit sections.

During a 24hr period there will be up to 7 separate TFT "pages of data sent".

Each page contains different weather info for each city and there are 480 pages sent containing data for 90 cities, 60 with a 4-day forecast and 30 with a two-day forecast.

The illustration below shows the weather page for Klagenfurt in Austria and is built up over 3 minutes.

Every minute the received "meteo" bits are checked and if OK the line Received Meteo Bits x-xx ae shown.

If the received meteo bits contain errors they will be rejected and the line for that data will be missing.

If the analyzer does not receive all these bits 1-14, 15-28 & 29-42 over the three minute period  the weather page can't be decoded and won't be displayed.

TFT Serial Monitor Detail

This sketch uses the built in hardware scrolling feature of the ILI9341 chip, this takes the processing burden off the Arduino AVR microcontroller and means that the display can keep up with serial text messages at 9600 baud.

The ILI9341 and GFX libraries been optimised for speed, some of the speed enhancing features use direct PORT access to the ATmega328 registers so it is important to use an Arduino board based on that processor chip.

These speed improvements means that characters in the proportional font 2 can be printed to the screen at more than 1000 characters per second.

The original sketch worked only at 9600 baud so I have added an option in the start menu to set the baud rate to 5 different values.

The rate required is set on the rotary control and then the Serial Monitor is reset by selecting "SET BAUD RATE" on the "RESET" non latching toggle switch so this new rate is loaded.

Once restarted the new board rate is shown on the top of the TFT.

The serial terminal can also read the serial output from external sources by selecting "EXTERNAL Prog. ESP32" on the "SERIAL SELECT" switch.

With the switch in this position the external serial port on the back on the DCF77 Analyzer is selected.

The external source's 0v should be connected to 0v of the Analyzer.

With the switch in this position and no external source selected anything that was connected on the internal port is "freeze framed".

This is useful for reading the 1 second output from the Filter as it scrolls every second.

When set to "INTERNAL" the "INT SERIAL SELECT" latching switch becomes live.

When set to "ANALYZER" the serial port output of the TFT analyzer is displayed on the TFT display.

When set to "FILTER" the serial port output of the DCF77 Filter  is displayed on the TFT display.

Arduino Serial Buffer Modification

I have modified the serial buffer on the serial monitor from 64 to 1024 so it should be able to handle faster baud rates.

The serial monitor UNO does nothing else but print out what's on the serial port so it has memory to spare.

To do this on my Arduino version 1.8.5 go to the Arduino core code directory and copy the Arduino folder.

My folder is in C:\Program Files (x86)\arduino-1.8.5\hardware\arduino\avr\cores

Paste the whole Arduino folder and then rename it to arduino_1024_serialbuf

Open this new folder C:\Program Files\arduino-1.0.1\hardware\arduino\cores\arduino_1024_serialbuf

and then look for the file USBAPI.h.

Open this folder in an editor.

Look for these lines

#ifndef SERIAL_BUFFER_SIZE

#if ((RAMEND - RAMSTART) < 1023)

#define SERIAL_BUFFER_SIZE 16

#else

#define SERIAL_BUFFER_SIZE 64

#endif

#endif

#if (SERIAL_BUFFER_SIZE>256)

#error Please lower the CDC Buffer size

#endif

Change buffer size the line in red to 1024.

You now have the following.

#ifndef SERIAL_BUFFER_SIZE

#if ((RAMEND - RAMSTART) < 1023)

#define SERIAL_BUFFER_SIZE 16

#else

#define SERIAL_BUFFER_SIZE 1024

#endif

#endif

#if (SERIAL_BUFFER_SIZE>256)

#error Please lower the CDC Buffer size

#endif

Save the file.

Next I modified the Boards.txt file.

My files was in the avr folder here  C:\Program Files (x86)\arduino-1.8.5\hardware\arduino\avr

Open the Boards.txt file in an editor

Locate the UNO board in the file see below

##############################################################

uno.name=Arduino/Genuino Uno

uno.vid.0=0x2341

uno.pid.0=0x0043

uno.vid.1=0x2341

uno.pid.1=0x0001

uno.vid.2=0x2A03

uno.pid.2=0x0043

uno.vid.3=0x2341

uno.pid.3=0x0243

uno.upload.tool=avrdude

uno.upload.protocol=arduino

uno.upload.maximum_size=32256

uno.upload.maximum_data_size=2048

uno.upload.speed=115200

uno.bootloader.tool=avrdude

uno.bootloader.low_fuses=0xFF

uno.bootloader.high_fuses=0xDE

uno.bootloader.extended_fuses=0xFD

uno.bootloader.unlock_bits=0x3F

uno.bootloader.lock_bits=0x0F

uno.bootloader.file=optiboot/optiboot_atmega328.hex

uno.build.mcu=atmega328p

uno.build.f_cpu=16000000L

uno.build.board=AVR_UNO

uno.build.core=arduino

uno.build.variant=standard 

##############################################################

Copy the section of txt  and paste it below.

Modify the txt you have just pasted as below.

 1024 has been added after the uno on each line and the build.core line has the arduino replaced by arduino_1024_serialbuf.

This is the name of your new folder where your modified USBAPI.h file is located.

##############################################################

Uno1024.name=Arduino Uno (1024 Serial Buffer)

uno1024.vid.0=0x2341

uno1024.pid.0=0x0043

uno1024.vid.1=0x2341

uno1024.pid.1=0x0001

uno1024.vid.2=0x2A03

uno1024.pid.2=0x0043

uno1024.vid.3=0x2341

uno1024.pid.3=0x0243

uno1024.upload.tool=avrdude

uno1024.upload.protocol=arduino

uno1024.upload.maximum_size=32256

uno1024.upload.maximum_data_size=2048

uno1024.upload.speed=115200

uno1024.bootloader.tool=avrdude

uno1024.bootloader.low_fuses=0xFF

uno1024.bootloader.high_fuses=0xDE

uno1024.bootloader.extended_fuses=0xFD

uno1024.bootloader.unlock_bits=0x3F

uno1024.bootloader.lock_bits=0x0F

uno1024.bootloader.file=optiboot/optiboot_atmega328.hex

uno1024.build.mcu=atmega328p

uno1024.build.f_cpu=16000000L

uno1024.build.board=AVR_UNO

uno1024.build.core=arduino_1024_serialbuf

Serial monitor showing decoded weather info after 3 consecutive error free minute decodes.

There are 480 of these pages in a day making up the weather/forecast for the DCF77 area       

14 encrypted weather bits are transmitted every minutes making 42 bits in total

The transmission starts again after 24 hours at 10 p.m. UTC with region 0.

A total of 90 regions in Europe are supplied with weather data.

60 with a 4-day forecast and 30 with a two-day forecast. This results in the following sequence:

Start at 10 p.m. UTC with
region 0 - 59 maximum values ​​1st day (today)
region 0 - 59 minimum
values 1st day (today) region 0 - 59 maximum values ​​2nd day (tomorrow)
region 0 - 59 minimum values 2nd day (tomorrow)
Region 0 - 59 maximum values ​​3rd day
Region 0 - 59 minimum
values 3rd day Region 0 - 59 maximum values ​​4th day
Region 0 - 59 Weather anomalies and wind data for the 4th day.
Since no minimum values ​​are transmitted for the 4th day, one uses the capacities freed up for
region 60 - 89 maximum values ​​1st day
region 60 - 89 maximum values ​​2nd day

It should be noted that the data for two regions are transmitted in the last 60 data records transmitted.

DCF77 Super Filter Detail

The Super Filter uses an Atmega 328 (UNO) IC to process the DCF77 signal.

The incoming DCF77 signal is monitored on the "DCF77 SIGNAL" led.

The filtered signal is monitored on the "DCF77 FILTERED" led. With a noiseless signal the  "DCF77 SIGNAL" & "DCF77 FILTERED" led will flash in unison.

Any slight difference is shown on the "SIGNAL DIFF" led.

With a noisy DCF77 signal  the "DCF77 SIGNAL" will flash with the noise on the signal but the filtered LED once the filter us in sync will flash correctly as the filter knows what pulse to expect next and will "SYNTHESIZE" it if not present.

Below noisy signal. Note the "DCF77 FILTERED" led pulses as normal despite the noise.

LED Function Chart

Name	Description
Filter On	lights when the DCF77 Source switch is set to FILTER and means the Super Filter is decoding and synthesizing the DCF77 signal
DCF77 Filtered	the DCF77 Synthesized signal coming out from the Super Filter
DCF77 Signal	the DCF77 signal coming direct from the DCF77 receiver with no filter applied
Signal Difference	the difference between the incoming DCF77 signal and the Synthesized signal. In normal operation this will flash as the received signal shape is often slightly “wider” than the synthesized signal.
Filter Synchronized	best possible quality, clock is 100% synced
Filter Locked	clock driven by accurate phase, time is accurate but not all decoder stages have sufficient quality for sync
Sync Lost <200mS	clock was once synced, inaccuracy below 200 ms, may re-lock if a valid phase is detected
Sync Lost >200mS	clock was once synced but now may deviate more than 200 ms, must not re-lock if valid phase is detected
Signal Dirty	time data available but unreliable
Signal Bad	waiting for good enough signal

Details

Filter Synchronized - Timing is completely locked to DCF77 and the data is most up to date.

Filter Locked - If the quality factor of the decoder stages drops but the quality factor of the phase decoder stays high enough the clock will transition into the state locked.

In this state it is still phase locked to DCF77 but it may become out of sync by a second but only if a leap second is transmitted.

Sync Lost <200mS - This indicates that the quality factor of the decoder stage and the quality factor of the phase decoder have dropped. In this state the timer relies on the quartz crystal timings and the clock will slowly drift out of phase with the DCF77 signal. This is a warning that the clock may be running slightly out of sync.

Sync Lost >200mS - Once the clock has started to drift out of phase for more than a set period of time (depending on the tuned accuracy of the quartz crystal) then this LED will light

Main Panel with the serial monitor switched to monitor the filter that outputs every second

DCF77 Filter Switches

Note in any switch position the DCF77 signal is always connected to the Filter.

This alows the Filter to always learn the signal and also tune the Quartz crystal.

This switch turns the DCF77 signal On or off

This switch turns the DCF77 Filter on or Off

This switch selects the filter type

Filtered Output –  If the clock is at least in state “locked” the output is synthesized and thus 100% clean.

The phase will be spot on but it might leap for 1s at unexpected times if can not properly decode the leap second announcement bit while a leap second is actually scheduled.

 In less than “locked” states it will pass the signal through. This is the most defensive modes which provides least filtering. If your DCF77 signal is not total crap it may be more than sufficient.

Synthesized Output – This is the most aggressive filter mode.

 After its initial sync it will synthesize no matter what the internal state is.

 However beware: if you do not evaluate the diff pin you will never know that it may be running “free” and thus drifting out of sync slowly.

Of course if the signal is reasonable every once in a while it will re-sync though.

Filter starting up.

Signal is shown as "SIGNAL BAD" as the filter is waiting to sync to the signal.

During this time if a noisy signal is received the filter will not correct it.

The noise is passed to the DCF77 decoder as shown by the DCF77 Signal and DCF77 Filtered LEDs flashing out of time every now and then as noise is received.

It will however keep learning looking for repeating patterns in the signal even though the signal is noisy.

As the filter learns the signal the "Signal Bad" LED will go out and the "Signal Dirty" LED will light.

This indicates that time data is available but is unreliable.

This is flowed by the "Filter Locked" LED.

This indicates that the clock is driven by accurate phase, time is accurate but not all decoder stages have sufficient quality for sync.

Filter in Sync

After a few minutes and it may be many if the signal is very noisy the filter will synchronize indicated by the "Filter Sync" led illuminating.

This indicates best possible quality, clock is 100% synced.

The "Signal Difference" LED will flash to show the difference between the incoming DCF77 signal and the Synthesized signal.

In normal operation this will flash as the received signal shape is often slightly “wider” than the synthesized signal.

Rejecting a Noisy Signal

Now the filter is in sync the filter knows what pulse to expect so if any any noise is received the filter synthesizes the correct pulse.

You can see below that the "DCF77 Filtered" LED continues to flash every second despite the DCF77 Signal LED flashing out of time.

An in sync filter will now start to adjust the frequency of the Quartz crystal using the DCF77 signal as a reference.

If the DCF77 signal is lost for many days the clock will stay in sync.

Eventually the quartz crystal will drift and if less than 200mS the "No Sync< 200mS LED will light.

If the crystal drifts more than 200mS then the "No Sync>200mS LED will light.

Once the DCF77 signal is restored the filter will go back into sync again.

Super Filter- on power up the pin connections are displayed

Once powered up the serial display is updated once per second

The meaning is shown in the diagram below.

Control Panel Construction

I used 1mm aluminium sheet to make the panel.

The panel template is printed out from my CAD program onto paper. The TFT holes are cut out with a craft knife and the template is then placed over the blank alluminium sheet.

A marker pen is used to draw around the TFT cut outs onto the alluminium and the hole centers are marked with a center punch through the paper template.

Panel ready for cutting out and drilling

Cutout the holes for the TFTs with a scroll saw/jig saw and drill holes for screws, switches and control knob.

Prime and spray

Printout panel design including centers onto inkjet decal paper and apply to painted panel

Cut away inkjet transfer paper from all holes and cutouts.

Apply two coats of clear varnish.

Completed panel with all parts in place.

DCF77 Analyzer Mounted in a wooden box

Alternative upright wooden box

Box construction

Box is constructed from 9mm plywood.

The box parts are screwed in place.

Cutout for alluminium panel

Alluminium control panel in place

Box painted and lettering decal applied

Box Dimentions

Top view of sides and base

Dimentions

The plywood lid has a section cutout for the controls and displays on the alluminium panel.

Alluminium panel superimposed over the wooden lid showing relative locations of cutouts.

Note the extra cutout for the base of VR1.

Alluminium lid in place.

Atmega 328

Two Atmega 328s (UNOs) are used in this project, 1 for the serial monitor and the other for the DCF77 Super Filter.

The following pins are used.

Super Filter Pins	Serial Monitor Pins

Atmega 328 Pinouts

A Lolin D32 Pro v2 is used for the DCF77 Analyzer

Lolin D32 Pro

Lolin D32 Pro v2 pinout

Lolin D32 Pro v2 schematic

Click image for PDF version

Lolin D32 Pro v2 Pin Table

Pin	Default Configuration*	Optional Configuration*	Remarks / Prerequisites	Configuration
GPIO22	I2C_DEV(0):SCL			I2C Interfaces
GPIO21	I2C_DEV(0):SDA			I2C Interfaces
GPIO18	SPI_DEV(0):SCK			SPI Interfaces
GPIO19	SPI_DEV(0):MISO			SPI Interfaces
GPIO23	SPI_DEV(0):MOSI			SPI Interfaces
GPIO5	SPI_DEV(0):CS0 / LED0			SPI Interfaces
GPIO4	SPI_DEV(0):CS1	SD Card CS	when module sdcard_spi is used	SPI Interfaces
GPIO1	UART_DEV(0):TxD		Console (configuration is fixed)	UART interfaces
GPIO3	UART_DEV(0):RxD		Console (configuration is fixed)	UART interfaces
GPIO36	ADC_LINE(0)			ADC Channels
GPIO39	ADC_LINE(1)			ADC Channels
GPIO34	ADC_LINE(2)			ADC Channels
GPIO35	ADC_LINE(3)		VBat measurement (GPIO is not broken out)	ADC Channels
GPIO32	ADC_LINE(4)	TFT_LED	when TFT is connected	ADC Channels
GPIO33	ADC_LINE(5)	TFT_RESET	when TFT is connected	ADC Channels
GPIO25	DAC_LINE(0)			DAC Channels
GPIO26	DAC_LINE(1)			DAC Channels
GPIO0	PWM_DEV(0):0	MRF24J40/ENC28J60 RESET	when module mrf24j40/enc2860 is used	PWM Channels
GPIO2	PWM_DEV(0):1	MRF24J40/ENC28J60 CS	when module mrf24j40/enc2860 is used	PWM Channels
GPIO13	-	MRF24J40/ENC28J60 INT	when module mrf24j40/enc2860 is used
GPIO15	-
GPIO12	-	TS_CS	when TFT is connected
GPIO14	-	TFT_CS	when TFT is connected
GPIO27	-	TFT_DC	when TFT is connected

Pre-built board and modules

LM2596 Regulator

LM2596 Regulator Module drops the voltage down to 5v.

This is adjusted by the 10K preset resistor on the module.

Adjust this before connecting the Lolin,328s & TFTs to the board.

RTC DS3231 I2C

This module stores the time from the decoded DCF77 signal.

The built in clock has temperature compensation and has battery backup in case of power failure.

Note the RTC module is modified  by removing R5 so it  takes non rechargeable batteries.

Vero Board Layouts

Note SW3 & SW5 can be omitted from the Vero Board as they are replace by toggle switches on the control panel.

Vero board fully assembled & wired.

Schematic (click image for full size version)

TFT displays and LEDs can be controlled/dimmed off the Lolin D32 Pro AT-LED via a transistor and LDR if required.

 The command tft.setBrightness( 0 - 255 ) can be used to set brightness over 256 levels. I have used a similar idea here  DCF77 Analyzer Mk2

Testing the DCF77 Analyzer

My DCF77 Generator digital DCF77 output fed into the DCF77 Analyzer.

The DCF77 Analyzer displays on both should be exactly the same.

Code

TFT Analyzer v26 9600 baud	Serial Monitor v9	Super Filter v12