[idea] Wedding TODO

I hate you! Since when do we live together?

Someone asked me: What special thing would you do on your wedding day?

Introducing Vincent's time counter

For this special day, I would design my own electronic time counter featuring a GPS receiver module and a microcontroller.

Using the GPS module, one can receive super accurate current time from GPS satellites. This time standard named TAI is "a weighted average of the time kept by over 400 atomic clocks" [1]. It does not include any leap seconds (unlike the UTC), and is more like a free-running counter. "GPS time" can be accurate to less than 100 nanoseconds (see [2]).

LEDs would display the current count of seconds in binary since the initial time was set. Because 100 years is approximately 3,155,695,200 seconds, I would suggest 32 LEDs for a counter up to 4,294,967,295 (=(2^32 - 1), aka ULONG_MAX from limit.h).

Start sequence, on wedding day

The electronic board would have a button to start the counter. When pressing the button, a microcontroller would store the start time read from the GPS module in an One-Time Programmable memory (OTP memory). This memory cannot be rewritten. They are designed to store unchanging things like encryption keys.

Then, the microcontroller would calculate the time difference between current time and this initial time, to display it using the LEDs.

When you decide that you are officially married, you start the counter together.

Later

The electronic board might probably not survive for decades, but the initial time value can easily be uploaded in one or several new boards.

References

[1]Marc Brett, "How accurate is the TIME DISPLAY on my GPS?", http://gpsinformation.net/main/gpstime.htm
[2]Wikipedia, "International Atomic Time" article, https://en.wikipedia.org/wiki/International_Atomic_Time