[time-nuts] Re: Clock display on Linux systems?

[John Miller]

This is something I have explored from time to time in order to find
a good local display option for Pis running as GIS-disciplined NTP
servers. I've done a lot of exploring and fiddling around with different
options but have yet to find a solution that I am fond of, for the
reasons that you describe.

I've had the most luck with TM1638-based boards, which often have eight
7-segment digits, plus LEDs and buttons, and can be had very cheaply.
They are easy to drive and a few different c-based code examples exist
for using them as clock displays on a Pi.

https://github.com/mjoldfield/pi-tm1638

https://mjoldfield.com/atelier/2012/08/pi-tm1638.html

The MAX7219 based units may be better as clocks - eight digits with no
buttons, but I don't have any on hand to test with.

I am very curious to see what suggestions folks come up with. I think
that the key question you need to answer is just how accurate do you 
want
this display to be? is +/-10ms acceptable, or does it need to be better?


John



-------- Original Message --------
Subject: [time-nuts] Clock display on Linux systems?
Date: 2021-12-05 3:53 pm
 From: Adam Space <time.isanapp at gmail.com>
To: Discussion of precise time and frequency measurement 
<time-nuts at lists.febo.com>

Most distributions of Linux already have a "clock" application that 
shows
the system time, but I am wondering how to program a more customizable
display on a Linux system / Raspberry pi. There are a few solutions that
pop up by googling the issue, but these are all insufficient. For 
example,
the only solutions in Python (which I would prefer to use if possible, 
but
not necessary) I have found are 1) using a library like pygame or 
tkinter
to build a display or 2) doing something more barebones like displaying 
the
time and sleep() ing for a second. 1) is terribly inefficient for a 
display
of accurate time, because either you have a refresh rate that is low and
the clock updates with significant lag, or you have a high refresh rate
which eats up large processing power. 2) is also inefficient because the
frequency of a local clock may be poor, so long term accuracy can only 
be
sustained with synchronization via NTP for example.

Perhaps there are lower level Linux commands that could be used for 
this?
I'm not sure. Any suggestions are welcome.

Adam
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