A custom desk clock for aviators showing the current UTC and local time as well as BCMT (beginning of civil morning twilight - the start of daytime) and ECET (end of civil evening twilight - the start of nighttime).

The clock is kept accurate using NTP synchronization. And will show a failure if the sync becomes to old.

It is a custom firmware for the ESP32 based LILYGO T-Display-S3 hardware.

Currently, the location and the timezone of the clocks local time need to be configured in the source code in config.h

The correct timezone strings can be looked up in the TZdef.h of the gmag11/ESPNtpClient project.

Configuration example:

// Set the location of the clock for BCMT and ECET calculation
// the default is Vöslau Airfield in Austria, LOAV
#define LATITUDE 47.964444 // in decimal degrees, with North being positive
#define LONGITUDE 16.259444 // in decimal degrees, with East being positive

// Set the timezone for the local time, the default is Vienna time.
#define TIMEZONE "CET-1CEST,M3.5.0,M10.5.0/3"

#define NTP_SERVER "0.pool.ntp.org"
### Build and upload

It can then be built and uploaded using platformio.

The WiFi is configured dynamically using a web interface provided by WiFiManager. If no WiFi is configured or the WiFi connection times out an access point with the SSID "aviators-desk-clock" is opened for configuration management.

You can connect your device to this access point and use the provided web interface to set the WiFi SSID and password for the WiFi which the clock should use.

After booting the clock it will perform it's first NTP sync, which can take a while, and you will see an INOP flag instead of the time.

The top of the two front buttons shuts the clock down into a sleep mode and wakes it up again.

The bottom of the two front buttons can be used to switch between the debug information page and the clock.

BCMT and ECET are shown in UTC. Therefore, the BCMT or ECET shown might actually be for the previous or next day in the UTC timezone.

If no BCMT or ECET exists, as is e.g. the case for locations above the arctic circle on certain days, NONE is shown instead.

The BCMT and ECET calculation are performed using the sunset library for Arduino.

BCMT and ECET are calculated for the current local date day but shown in UTC. Therefore, BCMT or ECET can actually be on a different UTC day.

Both are returned in fractional minutes, which are then floored and converted to hours and minutes. Therefore, a one-minute difference may be observed compared to other clocks or lists, depending on which treatment of seconds those sources choose. In this clock seconds are simply cut off, therefore for example 17:59:55 would be shown as 17:59 as would 17:59:01.

Please also note that some other sources report BCMT and ECET for average years, which will also cause a difference. The Austrian AIP for example states that a difference of up to 3 minutes is possible between an actual and average year for the tabulated times (GEN 2.7-1.4).

By default, a font based upon a simulation of the A320 engine indication system is used.

To replace the font it needs to be converted using the lvgl online font converter and can then be loaded and used in clock_gui.cpp.