Introduction: Arduino DCF77 Signal Analyzer Clock
Arduino DCF77 Clock & Signal Analyzer
You can also see this clock on myweb site here DCF77 Analyzer Clock page
This Clock displays the received & decoded DCF77 time code on three 8x8 dot matrix displays and time, date and signal info on four 8 digit 7 segment displays.
It uses 2 x Atmega 328 microprocessors (Arduino Uno) , 1 to control the DCF77 Analyzer and 1 to control a Udo Klein Super Filter. The Super Filter is switchable and will allow reception of the DCF77 signal from a very noisy signal.
The display auto dims controlled by a LDR and auto shuts down controlled by a PIR when no movement is detected.
See my 4K video of the clock running here
This clock is based on a DCF77 Analyzer Clock by Erik de Ruiter. See picture 3.
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Step 1: Clock Functions & Features
Receive and display, second by second the DCF77 coded signal from the transmitter in Germany.
Display the received signal on a 8x8 dot-matrix display. Once received and if error checked OK display the stored data on a 2nd 8x8 dot-matrix display, update the real time clock & display time and date on the top two 7 segment display modules.
Display signal error codes, signal status, day of the week and display intensity on a 3rd dot-matrix display If received signal has errors use a real time clock to display the time, picture 1 shows an animation of a complete minute being received into the buffers.
Use four 7 segment display modules to show the buffer, DCF Bit, no of errors, Period Time & Pulse Width.
Switchable DCF77 signal filtering provided on a 2nd Atmega 328 IC using software by Udo Klein Remote controlled individual reset of DCF77 Analyzer & Super Filter, DCF77 sound On/Off and Super Filter status LEDs On/Off.
Picture 2 above shows a close up of front panel.
Picture 3 shows the details of the 3 LED dot matrix displays.
DCF77 code for the next minute is received in the buffer (matrix 1 left) @ 1 bit per second at the end of the minute and if error checked OK the buffer is loaded into the current display store (matrix 2 middle) and the real time clock (RTC) is updated matrix 3 right shows Day of week, display intensity, clock status and clock info
Step 2: The Super Filter
When switched on the Udo Klein's Super Filter actively processes the incoming DCF77 signal from the Antenna/receiver. Over a number of days of learning the Super Filter can 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.
Picture 1 Super Filter example
The top row shows the Super Filter turned on. Once synchronized and tuned into the signal the Super Filter will synthesize a good signal even when the signal is completely lost. On a noisy signal the Super Filter will search for known signal bits and keep itself synchronized to the transmitter. The bottom row shows the Super Filter turned off. Whatever signal is received (good or bad) is sent to the decoder. Note the Super Filter input is always connected to the incoming DCF77 Signal even if the Super Filter is turned off. As the Super Filter can take a few days to tune to maximum accuracy this ensures it is always tuned/synchronized at maximum accuracy to the DCF77 signal.
Picture 2 shows the Super Filter flow chart.
Step 3: Clock Case
The case for this clock is based on a Tesco Black Glass & Metal Lantern. The case has a hinged door that I have positioned on the right of the clock.
The top glass panels are a good fit for the 3 x dot matrix displays. I have added 18mm MDF top and bottom sections as well as 2 x 6mm plywood pieces to replace the side glass on the small top panels. These panels are sprayed in black silk to match the metal case. The original metal handle on top of the case is cut away and 2 slots to take the remnants of the handle are cut into the top MDF panel. Dimensions H27xW15xD15cm
Step 4: LED Dot Matrix Display Constrution
Picture 01 The display uses 3x 8x8 dot matrix display modules with onboard MAX7219 ICs.
Picture 02 A small aluminium bar is cut to size and 6 x holes are drilled to take the matrix module mounting bolts. Note on pre-built modules the lower connectors may need to be de-soldered and re-soldered on the rear of the boards. Use extra nuts and bolts as spacers over the exposed solder pads as required.
Picture 03. A clear Perspex sheet is then cut to size with mounting holes drilled and is fitted on top of the aluminium bar.
Picture 04. Print out the display on Lazertran decal transfer paper and fix to Perspex sheet making sure it is aligned with the dot matrix modules.
Let the paper dry and don't spray with acrylic varnish to keep the transfer opaque to act as a diffuser for the LEDs.
Picture 05. Add a final sheet of white paper behind the Perspex to complete the diffused effect. The heavier the paper the more diffused (and dimmer) the matrix LEDs will be.
You can offset this effect is the software by setting different intensity values for the 7 segment displays and matrix displays. Note if you don't want to use Lazertran you could print the display on white paper and fix it behind the Perspex.
Pictures 06 & 07. Completed display ready to be mounted into the case.
Step 5: Main Display Board Construction
The main display board to house the four 7 segment displays is made up from 2 Vero boards bolted together with L shaped insulated aluminium angles.
On the finished clock the main Vero Board housing the twin Arduinos is fixed to the top six mounting bolts.
Picture 01 & 02 show Vero boards bolted together to mount displays. Board fronts are sprayed black. Connection strips are soldered to the display boards.
The four 7 segment displays plugged into connection strips, positioned marked by the four labels. Power and serial connections for the displays are run on the front of the display board.
Step 6: Main Display Board Layout
Note board fronts are shown orange for clarity actual board fronts are spay painted black.
Picture 01 Shows front of display boards with 7 segment display connection strips in place.
Picture 02 shows 7 segment display modules mounted along with black wooden blocks for fixing Perspex neutral density contrast display cover. Note black tape colon masking on top display module.
Picture 03 shows 7 segment display modules on without Perspex neutral density contrast display cover. Without this cover the displays are hard to read in bright light.
Picture 04 shows Perspex neutral density contrast display cover with Letroset labeling applied. The perpex cover is fitted behind the main display glass for protection.
Picture 05 same display as picture 03 but with the Perspex neutral density contrast display cover fixed to wooden mounting blocks. The display is now easy to read in all lighting and the PCB and display parts are now hidden from view.
Picture 06 shows the Dot matrix and main display in place in the case.
Step 7: Main Display Board Rear & Main Board Mounting
Picture 01 shows the rear (solder side) of the display boards with the display strips soldered in place.
Picture 02 shows display boards with insulated aluminium angles bolted in place by 8 bolts. This secures the 2 vero boards together.
Picture 03 shows the main board fixed to rear of the display boards between the aluminium angles.
Not shown in the pictures are decoupling capacitors at every display module.
Step 8: Main Vero Board and Display Board Assembly
Pictures 01 & 02 Vero Layout of main board front and rear the Atemga 328 on thel eft controls the DCF77 Analyzer and displays. The Atmega 328 on the right controls the Super Filter.
The toggle switch controls the DCF77 input to the board either direct from the antenna/receiver, the Super Filter or Off no DCF77 Signal.
The wireless receiver, CP2102 with DTR, PIR detector and RTC modules all plug into the board.
Pictures 03 & 04 show the assembled main display board with all components and cable connected ready for installation into the clock.
Step 9: Modification of the RTC Time 7 Segment Display Module to Show Colon Digit Separators
Picture 01 The standard display only has decimal points to separate the digits.
Picture 02 To display colons on digit 3 and 6 these 2 digits are set to display "o" lower case letter O permanently
This illuminates the bottom 4 led segments only.
Picture 03 4 x strips of black plastic tape are then applied over the digits.
Picture 04 When lower case "o" is displayed all you see is colons.
Step 10: PIR Detector Setup & Mounting
Picture 01 shows the standard PIR Module.
Picture 02 shows the infrared diffuser removed. The diffuser is half painted black so it senses from the front half only. The PIR sensing transistor is now exposed.
Picture 03 Shows the underside of the PIR module with the transistor PIR sensor de-soldered.
Picture 04 Shows how the 3 wires to the PIR transistor are connected to the board and then to the transistor.
The module is screwed to the underside of the clock lid with the transistor mounted on the top of the lid.
Picture 05 shows the PIR diffuser in place. The PIR transistor is mounted under the diffuser pointing forward.
Sensitivity and time triggered are adjusted on the 2 presets on the PIR Module board.
Step 11: Remote Control
The remote control has four functions
1. DCF77 Pulse sound On/Off When switched On the incoming DCF77 Pulses can be monitored via the small active buzzer
2. Super Filter Reset This will reset the Super Filter and remove all the learned tuning and will start the Super Filter unsynced. The Super Filter Monitor LEDs if switched on will go out until the Filter resynchronizes itself
3. Super Filter Monitor LEDs These 3 LEDs monitor the function of the Super Filter LED1- DCF77 Second Pulse LED2 DCF77 Signal Good LED3- Synthesized difference
4. DCF77 Analyzer Clock Reset This will reset the clock and displays to zero and the clock will lose any sync it had. If the RTC had been previously set RTC time will be displayed. Note the Super Filter will not be reset and any learned tuning and sync will not be effected.
If remote control is not required then momentary switches can be used instead.
Pictures 01 & 02 The remote control is based on a PT2272 Wireless Receiver Module (433MHz version) and a PT2262 Wireless Transmitter Module (433MHz version)
I use the 433Mhz version here in the UK but there are 315Mhz versions available for use in other countries.
Picture 03 You can get a 315Mhz Transmitter ready built in a key fob including the separate receiver on Ebay. If you go for this option you just plug the receiver into the main display board and you are ready to go. This option does not seem to be available in 433 Mhz.
The 433Mhz option requires either a small remote transmitter to be constructed or a learning key fob can be purchased and learnt from your transmitter.
Picture 04 Remote Control Transmitter for 415Mhz boards
The left four switches mounted on a small piece of vero board. The transmitter is mounted on the reverse along with a 9v battery. See instructions supplied with the module for wiring.
Picture 05 Alternatively a learning key fob can be purchased and can be programmed from the transmitter using
the simple circuit above. A PCB link is used to connected the micro switch to the four inputs in turn so the key fob can be programmed.
Super Filter On/Off Control Switch
A single switch controls the Super Filter and has 3 positions On Super Filter - When On the Super Filter output is connected to the Analyzer Clock DCF77 input and 5v is connected to IC1 pin 5 (IDE pin 3) to light the Super Filter LED on display matrix 3. No Connection- When in this position the Analyzer Clock DCF77 input is not connected to any signal On DCF77 Signal- In this position the Analyzer Clock DCF77 input is connected directly to the DCF77 receiver/antenna. Note in all positions the Super Filter is connected to the directly to the DCF77 receiver/antenna so it alway remains in sync.
Step 12: Reading the Received and Decoded Matrix Buffer Displays Second 00 to 34
The received matrix buffer is on the left and contains the information for the next minute. The display is identical the
decoded matrix in the middle which shows the time, date etc for the current minute. After each minute (if error checking is OK) the Next Minute buffer data is loaded into the Middle Matrix and becomes the Current Minute. DCF77 data is received serially once per second and once the clock is in sync second 0 is loaded into buffer 00 (Matrix position M), second 1 into buffer 01 etc. When a bit value of 1 is received the LED for that segment is lit but will remain unlit if the value is 0.
Second 0 Buffer 00 Matrix Label M
This is the start of the minute and will always be 0.
Second 1 to 14 Buffer 01 to 14 Matrix Label 01 to 14
These bits contain licensed encrypted Weather data for Europe and is used by DCF77 weather clocks. This data is displayed but not used by this clock.
Second 15 Buffer 15 Matrix Label Flt This bit contains transmitter info and is 0 unless there are transmitter problems
Second 16 Buffer 16 Matrix Label LHr Summer time announcement normally 0. Set to 1 during hour before change. Second 17 Buffer 17 Matrix Label CEST Set to 1 when CEST (Central European Summer Time) is in effect. Second 18 Buffer 18 Matrix Label CET Set to 1 when CET (Central European Time) is in effect. Second 19 Buffer 19 Matrix Label LSec Leap second announcement. Set to 1 during hour before leap second.
Second 20 Buffer 20 Matrix Label S Start of encoded time. Always set to 1.
Second 21 to 27 Buffer 21 to 27 Matrix Label 01,02,04,08,10,20 & 40.
These bits contain the minutes and are added together to show minutes from 00 to 59. 21 minutes would have 01 and the 20 LEDs lit, likewise 53 minutes would have 01,02,10 & the 40 LEDs lit
Second 28 Buffer 28 Matrix Label P1
This bit shows even parity over minute bits 21–28. Parity is a basic form of error checking. A Parity bit is added to the end of a string of digits in this case 7 bits from buffer 21 to 27. The Parity bit indicates if the number of 1s in the buffer from 21 to 27 is even or odd. If the number of 1s is even using Even Parity the Parity bit is 0 and if the number of 1s is odd then the Parity bit is 1. For example if the minutes to be transmitted are 5. Buffer Bits (Yellow hi-light above) 01=1, 02=0, 04=1, 08=0, 10=0, 20=0 & 40=0 0r 1010000 if you add the number of 1s together you get 2. This is an even number so the Parity bit transmitted will be 0. Therefore the transmitter will send 1010000 & 0. At the receiver end the receiver does not know what code to expect but it knows to check the parity of bits 21 to 27. If when receiving the bits 21 to 28 a miss reading occurs for example bit 22 is received as a 1 not a 0 the resulting bits would be 11100000. The receiver would expect the last bit (Parity) to be 1 as there are a an odd number of 1s. This indicates an error in the received signal and the received buffer would be rejected as it contains errors.
Second 29 to 34 Buffer 29 to 34 Matrix Label 01,02,04,08,10 & 20.
These bits contain the hours and are added together to show hours from 00 to 23. 10 hours would have only the 10 LED lit , likewise 23 hours would have 01,02 & the 20 LEDs lit
Step 13: Reading the Received and Decoded Matrix Buffer Displays Second 35 to 59
Second 35 Buffer 35 Matrix Label P2
This bit shows even parity over minute bits 29 to 35. See explanation of Parity in P1 (seconds 28 above)
Second 36 to 41 Buffer 36 to 41 Matrix Label 01,02,04,08,10 & 20.
These bits contain the day of the month and are added together to show days from 01 to 31. The 10th of the month would have only the 10 LED lit , likewise the 23rd of the month would have 01,02 & the 20 LEDs lit
Second 42 to 44 Buffer 42 to 44 Matrix Label 01,02 & 04.
These bits contain the day of the week and are added together to show Day of week Monday=1, Sunday=7 Monday would have only the 01 LED lit , likewise Sunday would have the 01,02 & the 04 LEDs lit
Second 45 to 49 Buffer 45 to 49 Matrix Label 01,02, 04, 08 &10
These bits when added together contain the month number and range from 01 to 12. January would have only the 01 LED lit , likewise July would have the 01,02 & the 04 LEDs lit
Second 50 to 57 Buffer 50 to 57 Matrix Label 01,02, 04, 08, 10,20,40 & 80
These bits when added together contain the year number within the centuary and range from 00 to 99. Year 01 would have only the 01 LED lit , likewise the year 99 would have the 01,08, 10, & the 80 LEDs lit
Second 58 Buffer 58 Matrix Label P3
This bit shows even parity over minute bits 36 to 58. See explanation of Parity in P1 (seconds 28 above)
Seconds 59 Buffer 58 Matrix Label On the 59th second the minute mark no 1 or 0 are transmitted indicating the end of the buffer on the next received pulse the buffer is reset to 00.
Step 14: Reading the Day, Display Intensity and Status/Info Matrix Display
The 3rd LED Matrix display shows the Day, the display intensity, the clock status and also info and is split in four sections
This section simply shows the current day illuminated by an LED on the Matrix.
This section of 16 LEDs indicate the auto adjusted Matrix and 7 segment display intensities. The light level is checked once per second and the intensity is adjusted up and down accordingly.
Eight LEDs indicate clock status messages.
DCF: When lit this shows the DCF77 signal is OK Sync: When lit this shows the clock is synchronised to the DCF77 signal
PT: When lit this shows there is an error with the Period Time of the received signal
PW: When lit this indicates an error with the Pulse Width of the received signal
EoB: Lights when buffer is full before end of 60 second cycle
EoM: Lights when buffer is not full at end of 60 second cycle (end mark received too early)
BF: This indicates the Buffer is full and will normally light at the end of the 60 second receiving cycle. If will also light at other times when lots of error pulses are being received. When lit the buffer is reset to 00.
RTC: When there is an error with the Real Time Clock ie no stored time this will light
Eight LEDs indicate clock information
Sig: This LED will flash with the received signal Pulse Width and is not effected by the Super Filter if switched on
Spk: When lit this indicates the received signal speaker is activated and signal pulses can be heard through the speaker
Fltr: When lit the Super Filter is turned on and the incoming signal is being processed and synthesised.
LEDs: When lit the Super Filter monitor LEDs are turned on.
Rmte: Lights when any button on the remote is pressed.
Win: Lights when the clock is in Wintertime
Sum: Lights when the clock is in Summertime
Leap: Light when it is a leap year
This picture show a summary of all the data over a whole minute and the DCF77 Transmitted Code Translation for each Buffer value
Step 15: Schematic
Schematic 01 shows the main board and connection to the external modules.
Schematic 02 shows the connections to the 7 display modules.
A full size schematic can be downloaded from the enclosed zip file.
Step 16: Microcontroller Pin Connection Table
Atmega 328 IC1 & 2 Pin connections and functions
Step 17: Code
The main bulk of this code was written by Erik de Ruiter for his DCF77 Analyzer Clock
Erik has provided full details of his code here on GitHub. I have tried to keep his code as much as possible but as and where I have not used it I have commented it out. Where I have added or modified it I have added a comment starting // Brett
Download code in zip format here DCF77 Analyzer Code
View the code in my web page here View Code
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