3 // Copyright (C) 2019-2020 by Art Cancro <ajc@citadel.org>
5 // My perfect clock has no buttons and cannot be set manually. This version uses a WWVB receiver module
6 // attached to pin D9 of the Arduino, and sets the clock any time it receives a complete frame. The clock
7 // is kept without an RTC, simply using the millis() timer. When time is set, it is displayed on
8 // a 7-segment array connected using an HT16K33 decoder/driver (yes, an Adafruit backpack). Our display
9 // can also display at 15 different brightness levels, so we dim it when the room is dark to avoid
10 // blasticating a dark room with super-bright LED display.
12 // The clock is hard coded to use US Eastern time with DST in effect whenever WWVB is announcing it.
14 const uint8_t wwvb = 9; // pin on which WWVB signal will be received
15 const uint8_t greenled = 2; // An LED attached to this pin will illuminate if the time has been set within the last 24 hours
16 const uint8_t yellowled = 3; // An LED attached to this pin will illuminate if we are currently receiving a clean frame
17 const uint8_t redled = 4; // An LED attached to this pin will pulse for 1 ms every second
18 const uint8_t photocell = A0; // Attach a photocell with a 10K voltage divider to this pin
19 const uint8_t addr = 0x70; // I2C address of HT16K33 (using Adafruit backpack with digits on 0,1,3,4; dots on 2)
21 #define MILLISECONDS_PER_MINUTE 60080 // Nominally 60000; adjust if your board runs fast or slow
23 // This is a simple BCD-to-7-segment font. It includes 0x0A through 0x0F even though they're not needed for a time clock.
24 const uint8_t sevensegfont[] = { 63, 6, 91, 79, 102, 109, 125, 7, 127, 111, 119, 124, 57, 94, 121, 113 };
25 const uint8_t firstcolfont[] = { 0, 6, 91 }; // this version of the font is for the first position
27 #include <Wire.h> // I2C library to drive the HT16K33 display
31 unsigned long millisecond = 0;
32 unsigned long previous_millis = 0;
33 unsigned long last_sync = -86398000;
34 uint16_t displayBuffer[8]; // Digit buffer for HT16K33
35 int previous_minute = 61; // What the minute was previously; we use this to detect whether an update is needed
36 int this_pulse = 0; // Value of the current pulse received
37 int previous_pulse = 0; // Value of the previous pulse received (two "mark" bits == new frame)
38 int start_of_pulse = 0; // The value of the millis() timer when the current pulse began
39 uint8_t framebuf[60]; // We store the entire 60-bit frame here
40 uint8_t framesync = 0; // Nonzero if we've received all good pulses since the start of the frame
41 int position_in_frame = 0; // Where we are in the frame (1 bit per second)
42 int previous_signal = 0; // "high" or "low" received on the previous cycle (so we can do edge detection)
43 int time_is_set = 0; // nonzero when time has been set at least once
49 pinMode(LED_BUILTIN, OUTPUT); // The built-in LED will display the raw WWVB signal pulses
50 pinMode(greenled, OUTPUT); // This LED will illuminate if the time has been set within the last 24 hours
51 pinMode(yellowled, OUTPUT); // This LED will illuminate if we are currently receiving a clean frame
52 pinMode(redled, OUTPUT); // This LED pulses for 1 ms every second
53 pinMode(wwvb, INPUT); // Input pin for WWVB receiver signal
54 pinMode(photocell, INPUT); // Input pin for photocell
56 Wire.begin(); // Initialize I2C
58 Wire.beginTransmission(addr);
59 Wire.write(0x21); // turn on oscillator
60 Wire.endTransmission();
62 Wire.beginTransmission(addr);
63 Wire.write(0xE1); // brightness (max is 15)
64 Wire.endTransmission();
66 Wire.beginTransmission(addr);
67 Wire.write(0x81); // no blinking or blanking
68 Wire.endTransmission();
72 displayBuffer[2] = 16;
79 // Note: only write to the display when the readout needs to be updated.
80 // Speaking I2C on every loop iteration jams the WWVB receiver.
83 unsigned long m = millis();
84 digitalWrite(redled, (m%1000) ? LOW : HIGH);
85 if (m != previous_millis) {
86 millisecond += (m - previous_millis);
87 if (millisecond >= MILLISECONDS_PER_MINUTE) {
88 millisecond -= MILLISECONDS_PER_MINUTE;
102 int signal = digitalRead(wwvb); // is the input high or low right now?
103 digitalWrite(LED_BUILTIN, signal); // use the onboard LED to show the signal
105 if (signal && (!previous_signal)) { // leading edge of pulse detected
106 start_of_pulse = millis();
108 else if ((!signal) && (previous_signal)) { // trailing edge of pulse detected
109 pulse_length = millis() - start_of_pulse;
111 if (pulse_length > 150 && pulse_length < 250) { // "0" bit ~= 200 ms (represented as "0")
113 } else if (pulse_length > 450 && pulse_length < 550) { // "1" bit ~= 500 ms (represented as "1")
115 } else if (pulse_length > 750 && pulse_length < 850) { // marker bit ~= 800 ms (represented as "2")
118 this_pulse = 15; // bad pulse (represented as "15")
119 framesync = 0; // throw the whole frame away
122 // BEGIN -- THINGS TO DO AT THE END OF A PULSE
124 if ((this_pulse == 2) && (previous_pulse == 2)) { // start of a new frame!
126 if (framesync == 1) {
127 set_the_time(); // We have a whole good frame. Set the clock!
129 else if ((!framesync) && (time_is_set)) {
130 snap_to_zero(); // We don't have a whole frame, but we know it's :00 seconds now.
134 position_in_frame = 0;
137 if (framesync) { // yellow LED = we currently have frame sync
138 analogWrite(yellowled, 10); // (we run it at a low intensity)
141 digitalWrite(yellowled, LOW);
144 if ((framesync) && (position_in_frame < 60)) {
145 framebuf[position_in_frame++] = this_pulse;
148 previous_pulse = this_pulse;
150 // END -- THINGS TO DO AT THE END OF A PULSE
153 previous_signal = signal;
155 // Update the display only if it's a new minute.
157 if (time_is_set && (minute != previous_minute)) {
158 previous_minute = minute;
159 int h12 = (hour % 12) ;
160 if (h12 == 0) h12 = 12;
161 displayBuffer[0] = firstcolfont[h12 / 10];
162 displayBuffer[1] = sevensegfont[h12 % 10];
163 displayBuffer[2] = (hour<12) ? 0x06 : 0x0a; // AM or PM dot , colon always on
164 displayBuffer[3] = sevensegfont[minute / 10];
165 displayBuffer[4] = sevensegfont[minute % 10];
169 if ((m - last_sync) < 86400000) { // green LED = got a good sync in the last 24 hours
170 digitalWrite(greenled, HIGH);
173 digitalWrite(greenled, LOW);
178 // Write the display buffer to the display
182 Wire.beginTransmission(addr);
183 Wire.write(0x00); // start at address 0x0
184 for (int i = 0; i < 5; i++) {
185 Wire.write(displayBuffer[i] & 0xFF);
186 Wire.write(displayBuffer[i] >> 8);
188 Wire.endTransmission();
190 // set the brightness
191 int light_level = analogRead(photocell) / 64;
192 if (light_level < 1) {
195 if (light_level > 15) {
198 Wire.beginTransmission(addr);
199 Wire.write(0xE0 + light_level); // set the display brightness
200 Wire.endTransmission();
204 // Set the software clock to the WWVB time currently in the buffer
207 int i, newhour, newminute, dst;
209 // These six positions MUST contain marker bits.
210 // If any of them do not, we are looking at a corrupt frame.
211 int markers[] = { 0, 9, 19, 39, 49, 59 };
212 for (i=0; i<6; ++i) {
213 if (framebuf[markers[i]] != 2) {
218 newhour = (framebuf[12] ? 20 : 0);
219 newhour += (framebuf[13] ? 10 : 0);
220 newhour += (framebuf[15] ? 8 : 0);
221 newhour += (framebuf[16] ? 4 : 0);
222 newhour += (framebuf[17] ? 2 : 0);
223 newhour += (framebuf[18] ? 1 : 0);
224 if ((newhour < 0) || (newhour > 23)) {
225 return; // reject impossible hours
228 newminute = (framebuf[1] ? 40 : 0);
229 newminute += (framebuf[2] ? 20 : 0);
230 newminute += (framebuf[3] ? 10 : 0);
231 newminute += (framebuf[5] ? 8 : 0);
232 newminute += (framebuf[6] ? 4 : 0);
233 newminute += (framebuf[7] ? 2 : 0);
234 newminute += (framebuf[8] ? 1 : 0);
235 if ((newminute < 0) || (newminute > 59)) {
236 return; // reject impossible minutes
239 // advance 1 minute because WWVB gives the *previous* minute
241 if (newminute >= 60) {
242 newminute = newminute % 60;
246 // US Eastern time (yes it is hard coded)
249 // DST (FIXME make this adjustable)
250 dst = (framebuf[57] ? 2 : 0);
251 dst += (framebuf[58] ? 1 : 0);
253 case 0: // dst not in effect (make no adjustments)
255 case 2: // dst begins today (adjust if local hour > 2)
260 case 3: // dst is in effect (always adjust)
263 case 1: // dst ends today (adjust if local hour < 2)
270 // If we went back to the previous day, adjust so that hour > 0
275 // Set the software clock:
276 // * We have decoded the hour and minute from the signal
277 // * This function always gets called *after* the first pulse at :00, so we set the millisecond to 800
283 // Let's remember the last time we synced the clock
284 last_sync = millis();
288 // Adjust the time to :00.8 seconds at the nearest minute.
291 if ((millisecond > 0) && (millisecond < 15000)) { // If the second is from :00.0 to :15.0
292 millisecond = 800; // snap back to :00.8
294 else if (millisecond > 45000) { // If the second is :45.0 or above
295 millisecond = MILLISECONDS_PER_MINUTE + 800; // snap forward to :00.8 (minute will advance automatically)