This project consists of building a rather large wall clock that reliably displays the correct time in Southern California, be it PST or PDT. The idea for this clock is "install and forget". The clock is intended to be installed in our Robot Labs, so that we have an easy way to see the time, so that we don't forget to go home.
The plan is to replace two old style battery clocks that never have the right time, and constantly kill their batteries.
The clock display is a grid of Neo Pixels (WS2812B Led) arranged in 32 columns and 8 rows. The clock is driven by a Raspberry Pico W. Time is kept by a DS3132 chip with a CR2023 backup battery. Therefore, if AC power is lost, time will continue to be maintained, and the clock won't have to be reset. The battery should last many years if the clock mostly runs on AC.
The PICO W also has a wifi module. If the PICO W can connect to the interrnet, NTP time can be obtained, in which case the time should be accurate to within one second.
The inital time (and updated time) can come from three sources: the RTC backup, NTP, or manually via interaction with the code using Thorny.
The code for the PICO W is writen in micropython.
Python time on the Pico W, under the micropython enviroment is kept by using the machine.RTC module. It is unclear if this module is using the RP2040 chip's built-in RTC hardware. However, it doesn't really matter since this code doesn't depend on the RP2040's notion of time. But it is interesting to note that upon USB connection with Thorny the machine.RTC module is synced to the time of the host (i.e., Windows)
For display output, the DS3231 time value is used. If the year in the DS3231 is less than 2010, then we assume that the DS3231 does not know the time -- and an error condition is shown on the display. Time updates (synchronizations) are attemped at startup if the time is found to be invalid, and once every night at about 2 am. If a valid NTP time is obtained, then the DS3132 is updated to match NTP time. The time that the DS3231 is updated is recorded in EEPROM.
If the clock runs for more than about a month without being updated and/or checked by wifi/NTP, then the time is decleared to be stale. A stale time is indicated by blue colon between the hour and minute digits. Normally the colon is red.
This clock is programmed to show the pacific time zone. It is also programmed to automatically switch between daylight savings and standard time. The algorithem for switching depends on past and current government policy, so the code will need to change if the rules regarding daylight savings changes.
This code is hardwired to check for a list of wifi access points to gain connection to the internet. Currently this list includes the Brandon's house, and the school's Robotic rooms.
One feature of this clock is that it can change the color of the clock digits at different times of day, for different days of the week. We call these critical times. Currently the critical times are from 8:50pm till 9:05pm on Monday through Thursday -- since these are the times the robot team needs to cleanup and leave the lab. There is also a crital time near 3am, since this is the time the buiding alarm automatically arms itself.
A record is kept for each power up cycle, and each time the RTC is updated with NTP Time. There are 64 records for each activity, on a rollover buffer in EEPROM. This data can be accessed manually by interacting with the code using Thorny.