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.
90 unsigned long m = millis();
91 if (m != previous_millis) {
92 millisecond += (m - previous_millis);
93 if (millisecond >= millis_per_minute) {
94 millisecond -= millis_per_minute;
108 int signal = digitalRead(wwvb); // is the input high or low right now?
111 analogWrite(timecodeled, 10); // it's too bright on my board so we dim it; change to digitalWrite() if not needed
114 digitalWrite(timecodeled, LOW);
117 if (signal && (!previous_signal)) { // leading edge of pulse detected
118 start_of_pulse = millis();
120 else if ((!signal) && (previous_signal)) { // trailing edge of pulse detected
121 pulse_length = millis() - start_of_pulse;
123 if (pulse_length > 175 && pulse_length < 225) { // "0" bit ~= 200 ms (represented as "0")
126 else if (pulse_length > 475 && pulse_length < 525) { // "1" bit ~= 500 ms (represented as "1")
129 else if (pulse_length > 775 && pulse_length < 825) { // marker bit ~= 800 ms (represented as "2")
133 this_pulse = 15; // bad pulse (represented as "15")
134 framesync = 0; // throw the whole frame away
137 // BEGIN -- THINGS TO DO AT THE END OF A PULSE
139 if ((this_pulse == 2) && (previous_pulse == 2)) { // start of a new frame!
141 if (framesync == 1) {
142 set_the_time(); // We have a whole good frame. Set the clock!
144 else if ((!framesync) && (time_is_set)) {
145 snap_to_zero(); // We don't have a whole frame, but we know it's :00 seconds now.
149 position_in_frame = 0;
150 calibrate(); // calibrate the software timer
153 if (framesync) { // yellow LED = we currently have frame sync
154 digitalWrite(cleantimecodeled, HIGH); // (we run it at a low intensity)
157 digitalWrite(cleantimecodeled, LOW);
160 if ((framesync) && (position_in_frame < 60)) {
161 framebuf[position_in_frame++] = this_pulse;
164 previous_pulse = this_pulse;
166 // END -- THINGS TO DO AT THE END OF A PULSE
169 previous_signal = signal;
171 // Update the display only if it's a new minute.
173 if (time_is_set && (minute != previous_minute)) {
174 previous_minute = minute;
175 int h12 = (hour % 12);
178 displayBuffer[0] = firstcolfont[h12 / 10];
179 displayBuffer[1] = sevensegfont[h12 % 10];
180 displayBuffer[2] = (hour < 12) ? 0x06 : 0x0a; // AM or PM dot , colon always on
181 displayBuffer[3] = sevensegfont[minute / 10];
182 displayBuffer[4] = sevensegfont[minute % 10];
186 if ((m - last_sync) < 86400000) { // green LED = got a good sync in the last 24 hours
187 digitalWrite(last24led, HIGH);
190 digitalWrite(last24led, LOW);
195 // Write the display buffer to the display
198 Wire.beginTransmission(addr);
199 Wire.write(0x00); // start at address 0x0
200 for (int i = 0; i < 5; i++) {
201 Wire.write(displayBuffer[i] & 0xFF);
202 Wire.write(displayBuffer[i] >> 8);
204 Wire.endTransmission();
206 // set the brightness
207 int light_level = analogRead(photocell) / 64;
208 if (light_level < 1) {
211 if (light_level > 15) {
214 Wire.beginTransmission(addr);
215 Wire.write(0xE0 + light_level); // set the display brightness
216 Wire.endTransmission();
220 // Set the software clock to the WWVB time currently in the buffer
221 void set_the_time() {
222 int i, newhour, newminute, dst;
224 // These six positions MUST contain marker bits.
225 // If any of them do not, we are looking at a corrupt frame.
226 int markers[] = { 0, 9, 19, 39, 49, 59 };
227 for (i = 0; i < 6; ++i) {
228 if (framebuf[markers[i]] != 2) {
233 newhour = (framebuf[12] ? 20 : 0);
234 newhour += (framebuf[13] ? 10 : 0);
235 newhour += (framebuf[15] ? 8 : 0);
236 newhour += (framebuf[16] ? 4 : 0);
237 newhour += (framebuf[17] ? 2 : 0);
238 newhour += (framebuf[18] ? 1 : 0);
239 if ((newhour < 0) || (newhour > 23)) {
240 return; // reject impossible hours
243 newminute = (framebuf[1] ? 40 : 0);
244 newminute += (framebuf[2] ? 20 : 0);
245 newminute += (framebuf[3] ? 10 : 0);
246 newminute += (framebuf[5] ? 8 : 0);
247 newminute += (framebuf[6] ? 4 : 0);
248 newminute += (framebuf[7] ? 2 : 0);
249 newminute += (framebuf[8] ? 1 : 0);
250 if ((newminute < 0) || (newminute > 59)) {
251 return; // reject impossible minutes
254 // advance 1 minute because WWVB gives the *previous* minute
256 if (newminute >= 60) {
257 newminute = newminute % 60;
261 // US Eastern time (yes it is hard coded)
264 // DST (FIXME make this adjustable)
265 dst = (framebuf[57] ? 2 : 0);
266 dst += (framebuf[58] ? 1 : 0);
268 case 0: // dst not in effect (make no adjustments)
270 case 2: // dst begins today (adjust if local hour > 2)
275 case 3: // dst is in effect (always adjust)
278 case 1: // dst ends today (adjust if local hour < 2)
285 // If we went back to the previous day, adjust so that hour > 0
290 // Set the software clock:
291 // * We have decoded the hour and minute from the signal
292 // * This function always gets called *after* the first pulse at :00, so we set the millisecond to 800
298 // Let's remember the last time we synced the clock
299 last_sync = millis();
303 // Adjust the time to :00.8 seconds at the nearest minute.
304 void snap_to_zero() {
305 if ((millisecond > 0) && (millisecond < 15000)) { // If the second is from :00.0 to :15.0
306 millisecond = 800; // snap back to :00.8
308 else if (millisecond > 45000) { // If the second is :45.0 or above
309 millisecond = millis_per_minute + 800; // snap forward to :00.8 (minute will advance automatically)
314 // By determining how many timer ticks elapsed between two minute markers, we can calibrate our software clock.
315 // Nominally it is 60000 milliseconds, but the software clock tends to drift.
316 // So we start with an array of all 60000 ms, and we keep ten calibrations and average them.
319 static unsigned long mpm_array[10] = { 60000, 60000, 60000, 60000, 60000, 60000, 60000, 60000, 60000, 60000 };
320 static int mpm = 0; // next one to update
322 static unsigned long last_calib = -86398000;
323 unsigned long m = millis();
324 unsigned long mm = m - last_calib;
325 if ((mm > 50000) && (mm < 70000)) {
326 mpm_array[mpm++] = mm;
330 millis_per_minute = (mpm_array[0] + mpm_array[1] + mpm_array[2] + mpm_array[3]
331 + mpm_array[4] + mpm_array[5] + mpm_array[6] + mpm_array[7]
332 + mpm_array[8] + mpm_array[9]) / 10;