Displays the Raspberry Pi's time on a Sense Hat

Each digit is 3x4 pixels so the time is shown as:

H H

M M

on the Sense Hat

Rich Stillman (stillmanff) adds:

1. Added internal timer loop to make the clock work standalone instead of invoking cron
2. Added a 12 hour mode that can be toggled via the twelvehour boolean
3. Added a blinking LED as a "second hand" that can be toggled via the blinkingSecond boolean
4. Turned off the high order digit in single digit hours

Start with python clock.py &

If you don't want terminal output, use

Update 11/5/2018:
Changed blinking second pixel to include barometric pressure information.
Clock compares current pressure with pressure from a half hour ago (sliding window).
Displays green if rising, red if falling.
Program measures barometric pressure in in/Hg and rounds to 1/100th inch.

Update 1/21/2019:
Added joystick controls based on christmastree project
1. Center press on joystick turns display on/off
2. Joystick down dims display (sense.low_light = True)
3. Joystick up brightens display

Also, fixed time on/off logic to play nicely with switch display on/off.


Update 11/29/2019:
Updated code for Python3 compatibility. This only required changing the format
of print statements.


Update 12/29/2019: Tuned barometer behavior, which was way too sensitive to
trivial fluctuations. Barometer now averages the most recent five minutes
of readings and the oldest five minutes of readings, and looks for a change
of 0.01 in/hg or more. The five minute average is hardcoded but the tolerance
is parameterized to allow the sensitivity of the barometer to be tuned.
Changed look-back period to two hours, which is a useful length of time for
comparing barometric pressures. Look-back (in seconds) is also now
parameterized to allow for barometer tuning.

Update 1/1/2020: Added double blink on seconds icon if the barometer is rising
or falling more rapidly than a settable parameter. 

Note that the program is written to use the Pi upside down (power cable on top).
Therefore, the up/down logic of the joystick is inverted.

Update 1/8/2020: Improved accuracy of barometer prediction. Adjusted barometer
lookback to six hours, changed thresholds for triggering color changes in barometer
indicator. Remaining bug: clock stops collecting barometer readings when the display
is shut off.

Update 1/31/2020: Keep collecting barometer data when the display is off.
Made data retention time parameter more intuitive. Tuned the intervals and display color
threshholds to give better predictions.

Coming features:
1. Use accelerometers to automatically rotate the display
2. Press the joystick to temporarily display current barometric pressure

Note: None of the other PiHat sensors seem accurate enough for real world use.