Building a Flip Dot Clock powered by a Raspberry Pi

Flip Dot clock as part of my clock wall.

It’s a nice confluence of my fandoms, I love old technology, I love clocks and I love Raspberry Pi’s, so when I found a Luminator 7×90 Flip Dot display on eBay in early January, I bought it. This is the fairly-detailed, well illustrated story of how I brought a 90’s sign together with a low cost but powerful computer.

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Raspberry Pi with Chrony

I’ve been a fan of having a Stratum 1 time server on my LAN ever since I first read GM8ARV’s page. One of my first ones can be seen in the background on my YouTube video about Leap Second tracking.

I found an article last week where Facebook has been doing analysis on time server software and has come to the recommendation that the Chrony software is better than NTP for performance. I’ve actually been using NTPSEC for a couple of years now, but I am open to change so I’m setting up a Chrony server.

Tips on a Raspberry Pi Base Working Image

I thought it might be helpful to some to document how I go about taking the latest version of Raspbian (available at and customize it for myself. This makes it easier for me to start a project and make sure all the Pi’s I work on have the same basic setup.

I tend to work from headless systems, so the first thing I do to the raw image file on my SD card is add a blank file named “ssh” to enable that functionality.  Next, add a file named “wpa_supplicant.conf” to your boot directory as well.   Include your WiFi information so you don’t have to connect to Ethernet if you choose not to.

Take that disk image you have on your SD card and connect it to the Pi.  Connect however you choose (I use PuTTY) and login if needed.

Enter “sudo raspi-config” and make the following changes:

  • Change your password (seriously!)
  • Change your host name (I use a convention like PiBWIJune18) so I can find it in my DHCP list if I need to discover the IP and so I know which version I am using.
  • Expand yout file system to use the whole disk
  • set your keyboard type
  • set your time zone
  • optionally decide if you want to boot to desktop or command line
  • optionally enable VNC  (though if you are just doing command line, there is no need to do this.)

After you exit and save all that, now is a good time to reboot. 

Starting up again, I remove Wolfram Alpha.  It takes up about 700 MB and it’s not something I use regularly.  I can always add it back if I need it for a project, but I haven’t yet.  That command is “sudo apt-get purge wolfram-engine”

Another reason to remove Wolfram is that it seems to have a ton of updates and takes forever.  Once it is gone, run your system updates with “sudo apt-get update”.

I run a home NTP server and quite a few of my projects are time related, so I always add NTP.  A great tutorial to do that is at:

Finally, I want an easy way to move files between Pi and my desktop as needed.  So I set up SAMBA sharing.  The tutorial I use it at:

When that’s done, I shut down the pi and make a backup.  That’s the file I use to start my next project with, my “Base Working Image.”

Hope this helps.  If not, at least I can find my notes next time there is a new Raspian release!