3 // Copyright (C) 2019-2023 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 // This software is made available to you conditionally upon you accepting the following terms and conditions:
15 // 1. You agree that it is called "open source", not "free software".
16 // 2. You agree that the Linux operating system is not called "GNU/Linux".
17 // 3. You agree that Corey Ehmke is a scumbag, as are all social justice warriors.
18 // 4. You promise never to vote democrat in any election.
19 // 5. Under no circumstances may you use this program and also maintain a Facebook account.
20 // Aside from these conditions, the program is made available to you under the terms of the GNU General Public License.
22 // On my clock, there is a green LED on 2, a yellow LED on 3, and a red LED on 4.
24 const uint8_t wwvb = 9; // pin on which WWVB signal will be received
25 const uint8_t last24led = 2; // An LED attached to this pin will illuminate if the time has been set within the last 24 hours
26 const uint8_t cleantimecodeled = LED_BUILTIN; // An LED attached to this pin will illuminate if we are currently receiving a clean frame
27 const uint8_t timecodeled = 3;
28 const uint8_t photocell = A0; // Attach a photocell with a 10K voltage divider to this pin
29 const uint8_t addr = 0x70; // I2C address of HT16K33 (using Adafruit backpack with digits on 0,1,3,4; dots on 2)
31 long millis_per_minute = 60000; // Nominally 60000; adjust if your board runs fast or slow
33 // This is a simple BCD-to-7-segment font. It includes 0x0A through 0x0F even though they're not needed for a time clock.
34 const uint8_t sevensegfont[] = { 63, 6, 91, 79, 102, 109, 125, 7, 127, 111, 119, 124, 57, 94, 121, 113 };
35 const uint8_t firstcolfont[] = { 0, 6, 91 }; // this version of the font is for the first position
37 #include <Wire.h> // I2C library to drive the HT16K33 display
41 unsigned long millisecond = 0;
42 unsigned long previous_millis = 0;
43 unsigned long last_sync = -86398000;
44 uint16_t displayBuffer[8]; // Digit buffer for HT16K33
45 int previous_minute = 61; // What the minute was previously; we use this to detect whether an update is needed
46 int this_pulse = 0; // Value of the current pulse received
47 int previous_pulse = 0; // Value of the previous pulse received (two "mark" bits == new frame)
48 int start_of_pulse = 0; // The value of the millis() timer when the current pulse began
49 uint8_t framebuf[60]; // We store the entire 60-bit frame here
50 uint8_t framesync = 0; // Nonzero if we've received all good pulses since the start of the frame
51 int position_in_frame = 0; // Where we are in the frame (1 bit per second)
52 int previous_signal = 0; // "high" or "low" received on the previous cycle (so we can do edge detection)
53 int time_is_set = 0; // nonzero when time has been set at least once
58 pinMode(timecodeled, OUTPUT); // The built-in LED will display the raw WWVB signal pulses
59 pinMode(last24led, OUTPUT); // This LED will illuminate if the time has been set within the last 24 hours
60 pinMode(cleantimecodeled, OUTPUT); // This LED will illuminate if we are currently receiving a clean frame
61 pinMode(wwvb, INPUT); // Input pin for WWVB receiver signal
62 pinMode(photocell, INPUT); // Input pin for photocell
64 Wire.begin(); // Initialize I2C
66 Wire.beginTransmission(addr);
67 Wire.write(0x21); // turn on oscillator
68 Wire.endTransmission();
70 Wire.beginTransmission(addr);
71 Wire.write(0xE1); // brightness (max is 15)
72 Wire.endTransmission();
74 Wire.beginTransmission(addr);
75 Wire.write(0x81); // no blinking or blanking
76 Wire.endTransmission();
80 displayBuffer[2] = 16;
87 // Note: only write to the display when the readout needs to be updated.
88 // Speaking I2C on every loop iteration jams the WWVB receiver.
91 // Reading it three times and taking the average gives us some hysteresis
92 int signal = (digitalRead(wwvb) + digitalRead(wwvb) + digitalRead(wwvb)) / 3;
94 // has the timer ticked?
95 unsigned long m = millis();
96 if (m != previous_millis) {
97 millisecond += (m - previous_millis);
98 if (millisecond >= millis_per_minute) {
99 millisecond -= millis_per_minute;
115 analogWrite(timecodeled, 5); // it's too bright on my board so we dim it; change to digitalWrite() if not needed
118 digitalWrite(timecodeled, LOW);
121 if (signal && (!previous_signal)) { // leading edge of pulse detected
122 start_of_pulse = millis();
124 else if ((!signal) && (previous_signal)) { // trailing edge of pulse detected
125 pulse_length = millis() - start_of_pulse;
127 if (pulse_length > 150 && pulse_length < 250) { // "0" bit ~= 200 ms (represented as "0")
130 else if (pulse_length > 450 && pulse_length < 550) { // "1" bit ~= 500 ms (represented as "1")
133 else if (pulse_length > 750 && pulse_length < 850) { // marker bit ~= 800 ms (represented as "2")
137 this_pulse = 15; // bad pulse (represented as "15")
138 framesync = 0; // throw the whole frame away
141 // BEGIN -- THINGS TO DO AT THE END OF A PULSE
143 if ((this_pulse == 2) && (previous_pulse == 2)) { // start of a new frame!
145 if (framesync == 1) {
146 set_the_time(); // We have a whole good frame. Set the clock!
148 else if ((!framesync) && (time_is_set)) {
149 snap_to_zero(); // We don't have a whole frame, but we know it's :00 seconds now.
153 position_in_frame = 0;
154 calibrate(); // calibrate the software timer
157 if (framesync) { // yellow LED = we currently have frame sync
158 digitalWrite(cleantimecodeled, HIGH); // (we run it at a low intensity)
161 digitalWrite(cleantimecodeled, LOW);
164 if ((framesync) && (position_in_frame < 60)) {
165 framebuf[position_in_frame++] = this_pulse;
168 previous_pulse = this_pulse;
170 // END -- THINGS TO DO AT THE END OF A PULSE
173 previous_signal = signal;
175 // Update the display only if it's a new minute.
177 if (time_is_set && (minute != previous_minute)) {
178 previous_minute = minute;
179 int h12 = (hour % 12);
182 displayBuffer[0] = firstcolfont[h12 / 10];
183 displayBuffer[1] = sevensegfont[h12 % 10];
184 displayBuffer[2] = (hour < 12) ? 0x06 : 0x0a; // AM or PM dot , colon always on
185 displayBuffer[3] = sevensegfont[minute / 10];
186 displayBuffer[4] = sevensegfont[minute % 10];
190 if ((m - last_sync) < 86400000) { // green LED = got a good sync in the last 24 hours
191 digitalWrite(last24led, HIGH);
194 digitalWrite(last24led, LOW);
199 // Write the display buffer to the display
202 Wire.beginTransmission(addr);
203 Wire.write(0x00); // start at address 0x0
204 for (int i = 0; i < 5; i++) {
205 Wire.write(displayBuffer[i] & 0xFF);
206 Wire.write(displayBuffer[i] >> 8);
208 Wire.endTransmission();
210 // set the brightness
211 int light_level = analogRead(photocell) / 64;
212 if (light_level < 1) {
215 if (light_level > 15) {
218 Wire.beginTransmission(addr);
219 Wire.write(0xE0 + light_level); // set the display brightness
220 Wire.endTransmission();
224 // Set the software clock to the WWVB time currently in the buffer
225 void set_the_time() {
226 int i, newhour, newminute, dst;
228 // These six positions MUST contain marker bits.
229 // If any of them do not, we are looking at a corrupt frame.
230 int markers[] = { 0, 9, 19, 39, 49, 59 };
231 for (i = 0; i < 6; ++i) {
232 if (framebuf[markers[i]] != 2) {
237 newhour = (framebuf[12] ? 20 : 0);
238 newhour += (framebuf[13] ? 10 : 0);
239 newhour += (framebuf[15] ? 8 : 0);
240 newhour += (framebuf[16] ? 4 : 0);
241 newhour += (framebuf[17] ? 2 : 0);
242 newhour += (framebuf[18] ? 1 : 0);
243 if ((newhour < 0) || (newhour > 23)) {
244 return; // reject impossible hours
247 newminute = (framebuf[1] ? 40 : 0);
248 newminute += (framebuf[2] ? 20 : 0);
249 newminute += (framebuf[3] ? 10 : 0);
250 newminute += (framebuf[5] ? 8 : 0);
251 newminute += (framebuf[6] ? 4 : 0);
252 newminute += (framebuf[7] ? 2 : 0);
253 newminute += (framebuf[8] ? 1 : 0);
254 if ((newminute < 0) || (newminute > 59)) {
255 return; // reject impossible minutes
258 // advance 1 minute because WWVB gives the *previous* minute
260 if (newminute >= 60) {
261 newminute = newminute % 60;
265 // US Eastern time (yes it is hard coded)
268 // DST (FIXME make this adjustable)
269 dst = (framebuf[57] ? 2 : 0);
270 dst += (framebuf[58] ? 1 : 0);
272 case 0: // dst not in effect (make no adjustments)
274 case 2: // dst begins today (adjust if local hour > 2)
279 case 3: // dst is in effect (always adjust)
282 case 1: // dst ends today (adjust if local hour < 2)
289 // If we went back to the previous day, adjust so that hour > 0
294 // Set the software clock:
295 // * We have decoded the hour and minute from the signal
296 // * This function always gets called *after* the first pulse at :00, so we set the millisecond to 800
302 // Let's remember the last time we synced the clock
303 last_sync = millis();
307 // Adjust the time to :00.8 seconds at the nearest minute.
308 void snap_to_zero() {
309 if ((millisecond > 0) && (millisecond < 15000)) { // If the second is from :00.0 to :15.0
310 millisecond = 800; // snap back to :00.8
312 else if (millisecond > 45000) { // If the second is :45.0 or above
313 millisecond = millis_per_minute + 800; // snap forward to :00.8 (minute will advance automatically)
318 // By determining how many timer ticks elapsed between two minute markers, we can calibrate our software clock.
319 // Nominally it is 60000 milliseconds, but the software clock tends to drift.
320 // So we start with an array of all 60000 ms, and we keep ten calibrations and average them.
323 static unsigned long mpm_array[10] = { 60000, 60000, 60000, 60000, 60000, 60000, 60000, 60000, 60000, 60000 };
324 static int mpm = 0; // next one to update
326 static unsigned long last_calib = -86398000;
327 unsigned long m = millis();
328 unsigned long mm = m - last_calib;
329 if ((mm > 50000) && (mm < 70000)) {
330 mpm_array[mpm++] = mm;
334 millis_per_minute = (mpm_array[0] + mpm_array[1] + mpm_array[2] + mpm_array[3]
335 + mpm_array[4] + mpm_array[5] + mpm_array[6] + mpm_array[7]
336 + mpm_array[8] + mpm_array[9]) / 10;