// The clock is hard coded to use US Eastern time with DST in effect whenever WWVB is announcing it.
+// This software is made available to you conditionally upon you accepting the following terms and conditions:
+// 1. You agree that it is called "open source", not "free software".
+// 2. You agree that the Linux operating system is not called "GNU/Linux".
+// 3. You agree that Corey Ehmke is a scumbag, as are all social justice warriors.
+// 4. You promise never to vote democrat in any election.
+// 5. Under no circumstances may you use this program and also maintain a Facebook account.
+// Aside from these conditions, the program is made available to you under the terms of the GNU General Public License.
+
const uint8_t wwvb = 9; // pin on which WWVB signal will be received
const uint8_t greenled = 2; // An LED attached to this pin will illuminate if the time has been set within the last 24 hours
const uint8_t yellowled = 3; // An LED attached to this pin will illuminate if we are currently receiving a clean frame
const uint8_t photocell = A0; // Attach a photocell with a 10K voltage divider to this pin
const uint8_t addr = 0x70; // I2C address of HT16K33 (using Adafruit backpack with digits on 0,1,3,4; dots on 2)
-#define MILLISECONDS_PER_MINUTE 60080 // Nominally 60000; adjust if your board runs fast or slow
+long millis_per_minute = 60000; // Nominally 60000; adjust if your board runs fast or slow
// This is a simple BCD-to-7-segment font. It includes 0x0A through 0x0F even though they're not needed for a time clock.
const uint8_t sevensegfont[] = { 63, 6, 91, 79, 102, 109, 125, 7, 127, 111, 119, 124, 57, 94, 121, 113 };
digitalWrite(redled, (m%1000) ? LOW : HIGH);
if (m != previous_millis) {
millisecond += (m - previous_millis);
- if (millisecond >= MILLISECONDS_PER_MINUTE) {
- millisecond -= MILLISECONDS_PER_MINUTE;
+ if (millisecond >= millis_per_minute) {
+ millisecond -= millis_per_minute;
++minute;
if (minute > 59) {
minute = 0;
framesync = 1;
position_in_frame = 0;
+ calibrate(); // calibrate the software timer
}
if (framesync) { // yellow LED = we currently have frame sync
millisecond = 800; // snap back to :00.8
}
else if (millisecond > 45000) { // If the second is :45.0 or above
- millisecond = MILLISECONDS_PER_MINUTE + 800; // snap forward to :00.8 (minute will advance automatically)
+ millisecond = millis_per_minute + 800; // snap forward to :00.8 (minute will advance automatically)
+ }
+}
+
+
+// By determining how many timer ticks elapsed between two minute markers, we can calibrate our software clock.
+// Nominally it is 60000 milliseconds, but the software clock tends to drift.
+void calibrate()
+{
+ static unsigned long last_calib = -86398000;
+ unsigned long m = millis();
+ unsigned long mm = m - last_calib;
+ if (50000 < mm < 70000) {
+ millis_per_minute = mm;
}
+ last_calib = m;
}