Decoding the WWVB “Atomic Clock” Signal

1/*
2  WWVB RECEIVER DECODER ---- Reads the 1 pulse per second time code from WWVB
3  Arduino UNO - - - L. Thomas - March 2024
4
5  Input 6 senses the NOT output signal of the WWVB Receiver from Universal-Solder.
6  Output 7 controls the PDN signal to the WWVB Receiver (enable/disable)
7  Input 2 receives the 60Hz power line signal and functions as an interrupt
8  A positive going edge on the NOT output signal kicks off decoding of the signal
9    each second.  Following this event, the NOT output signal is examined 21 AC cycles
10    later (350ms) to see if the signal is still HIGH (a 1) or if it is LOW (a 0).
11    If it was a 1 the signal is checked again after a total of 42 AC cycles (700ms)
12    to find out if it is still high and actually a Position Marker.
13  The green LED is turned on whenever the output signal is HIGH.
14  Uses 60Hz signal (pin 2, INT0) as interrupt for timing.
15  Displays "P" when an 800ms Position Marker is detected (6 per minute).
16  Displays "F" when 2 consecutive Position Markers are detected (1 per minute).
17  Display a "0" or "1" for BCD data detection each second.
18  Displays a "-" while waiting for a decoded result.
19*/
20//
21int Signal = 6;     // pin 6 connects to the WWVB receiver NOT output signal
22//                     NOTE: pin 6 also connects to S4 push-button
23int PDN = 7;        // pin 7 connects to the WWVB receiver PDN pin
24int GrnLED = 3;     // pin 3 is connected to the green LED
25int DataIn = 8;     // pin 8 is serial in data for the shift register
26int ClkIn = 9;      // pin 9 clocks data from pin 8 into the shift register
27int RegClk = 10;    // pin 10 clocks byte of data to the shift register outputs
28int OutEnable = 11; // pin 11, when LOW, enables the shift register output (HIGH disables)
29int Clear = 12;     // pin 12, when LOW, clears the shift register to all zeros
30int Sigtest = 0;          // Used to watch for positive going edge of receiver NOT output
31int PMflag = 0;           // Used to record that a Position Marker was decoded
32int Pmark = 43;           // AC count in Decode to decode a 1 or a Position Marker (700ms) 
33int Dmark = 22;           // AC count value in Decode to decode either a 0 or a 1 (350ms)
34int Sigend = 55;          // AC count limit - point to reset and decode next digit
35int Digit = 0;            // Digit = 0 or 1 for BCD values, or 2 for a Position Marker
36//                            or 3 for a Frame Marker (2 consecutive Position Markers)
37volatile int SUBsec = 1;  // Accumulates 60 AC cycles for each second of the clock
38volatile int Seconds = 0; // Accumulate seconds up to 59 then is reset to 0
39//                            (The above 2 are for future use of digital clock)
40volatile int Decode = 1;  // Accumulates AC cycles for BCD data decoding
41//                            Decode is set to 1 at the positive going edge of
42//                            the WWVB receiver NOT output signal (on pin 6). It is
43//                            incremented each AC cycle until it reaches Sigend (55)
44byte Chardash = 64;       // Value to display a "-"
45//
46//Contents of array below are values for display of a 0, 1, P, and F
47byte AllDigts[] = {63, 6, 115, 113};
48//
49// The setup routine runs once during start-up or when RESET is pressed.
50// The setup commands are inside the pair of curly braces following "void setup()"
51void setup()
52{
53  pinMode(Signal, INPUT);       // Sets the WWVB NOT signal as an input (also S4)
54  pinMode(PDN, OUTPUT);         // Sets the WWBV PDN control as an output
55  pinMode(2, INPUT);            // Sets pin 2 as the 60Hz interrupt input
56  pinMode(DataIn, OUTPUT);      // This sets pin 8 as an output
57  pinMode(ClkIn, OUTPUT);       // This sets pin 9 as an output
58  pinMode(RegClk, OUTPUT);      // This sets pin 10 as an output
59  pinMode(OutEnable, OUTPUT);   // This sets pin 11 as an output
60  pinMode(Clear, OUTPUT);       // This sets pin 12 as an output
61  pinMode(GrnLED, OUTPUT);      // This sets pin 3 as an output
62//
63  digitalWrite(DataIn, LOW);    // Make shift register data pin a zero (LOW)
64  digitalWrite(ClkIn, LOW);     // Initialize the shift register input clock to LOW status
65  digitalWrite(RegClk, LOW);    // Initialize the shift register clock pin LOW
66  digitalWrite(OutEnable, LOW); // Enable the shift register output
67  digitalWrite(Clear, HIGH);    // Initialize the CLEAR pin to HIGH (not cleared)
68  digitalWrite(PDN, HIGH);      // Initialize the PDN signal as HIGH (Receiver off)
69  delay (250);                  // Delay a bit
70  digitalWrite(PDN, LOW);       // Now let the WWVB receiver operate - PDN is LOW
71  attachInterrupt(0, Update, RISING); //Enable the interrupt now
72}
73// Now that the setup has been done, the main loop is started
74// **** MAIN LOOP *********************************************************************
75void loop() {
76if (Decode >= Dmark)                           //Display a "-" during decode time
77{                                              // otherwise show value of Digit
78  shiftOut(DataIn, ClkIn, LSBFIRST, Chardash); //This loads a "-" into the shift register
79  DisplayON();                                 //then displays it
80}
81  else                                         //Display number or letter as per Digit
82//                                               This shows what was just decoded
83{                                              // in the previous second
84  shiftOut(DataIn, ClkIn, LSBFIRST, AllDigts[Digit]); //This loads a digit from
85  DisplayON();                                 //  the array into the shift register
86}                                              //  and displays it
87//
88//  The following catches the positive going edge of the WWBV receiver NOT output
89  if (digitalRead(Signal) == HIGH)             //Watch for positive going edge of Signal
90{
91  Sigtest = 1;                                 //It is HIGH so make Sigtest = 1 and
92  digitalWrite(GrnLED, HIGH);                  //Turn on the green LED
93}  
94  else
95{
96  Sigtest = 0;                                 //It is LOW so make Sigtest = 0 and
97  digitalWrite(GrnLED, LOW);                   //Turn off the green LED
98}
99  if (Sigtest == 0 && Decode >= Sigend)        //Signal now returned to LOW. At end of testing?
100  Decode = 0;                                  //Yes, Reset for next digit test
101  if (Sigtest == 1 && Decode == 0)             //Found a positive going edge?
102{
103  Decode = 1;                                  //Yes, kick off reading of a new digit
104  //                                              and display what we just decoded
105  shiftOut(DataIn, ClkIn, LSBFIRST, AllDigts[Digit]); //This loads a digit from
106  DisplayON();                                 //  the array into the shift register
107}                                              //  and displays it
108}                                              //END OF LOOP
109// ************************************************************************************
110void DisplayON()                            //This function activates the display
111{
112  digitalWrite(RegClk, HIGH);               //Clock the data to the output register
113  digitalWrite(RegClk, LOW);                //Put Clock signal back low - creating a pulse
114  digitalWrite(ClkIn, LOW);                 //Be sure clock is initialized to LOW status
115}
116//
117// Interrupt Service - Accumulates AC cycles  *****************************************
118  void Update (void)                   //This is executed once each 60Hz AC cycle
119{
120  Decode = Decode + 1;                 //Add 1 AC cycle to Decode counter
121  SUBsec = SUBsec + 1;                 //Add 1 AC cycle to the sub-seconds counter
122//   Clock update:  (for future use)
123  if (SUBsec > 59)                     //Do we have a new second?
124{
125  SUBsec = 0;                          //Yes-so reset for another
126  Seconds = Seconds + 1;               // and increment the seconds    
127}
128  if (Seconds > 59)                    //Limit Seconds to 59 then reset
129  Seconds = 0;
130//   WWVB Decode update:
131  if (Decode == 1)                     //Don't increment Decode if it was at 0 and now 1
132  Decode = 0;                          //Put it back to zero (wait for new signal edge)
133  if (Decode == Dmark && Sigtest == 1) //Time to check - Is it a 1? (22)
134  Digit = 1;                           //HIGH makes it a 1
135  if (Decode == Dmark && Sigtest == 0) //Time to check - Is it a 0? (22)
136{
137  Digit = 0;                           //LOW makes it a 0
138  PMflag = 0;                          //Can't be a Position Marker so reset this
139}
140  if (Decode == Pmark && PMflag == 1 && Sigtest == 1)
141//                                       Check PMflag for a 2nd Position Marker
142  Digit = 3;                           //Yes, so it is a Frame Marker
143  if (Decode == Pmark && Digit == 1 && Sigtest == 1)
144//                                       Check for a first Position Marker?
145//                                       Digit will not change if Signal is LOW
146{
147  Digit = 2;                           //Still HIGH so we have a Position Marker
148  PMflag = 1;                          //And record this event (might get 2 in a row)
149}}
150// End of Interrupt Service: *********************************************************