Status: Compiles, tested
I was given a set of nixie tubes long time ago as a gift and had a design for a clock but never got to the point of laying it out. I found on Etsy and ebay was that GRA+AFCH selling clock boards. This design is an add-on board to an Arduino which has tube sockets, high voltage switcher, high voltage serial to parallel ICs, and real time clock. The kicker being that the tubes are much harder to get and very expensive. By exploring their web site I found they had a Pi Shield, which does all of the necessary Pi to Arduino level shifting. Unfortunately none of their cases will fit the raspberry pi.
I wanted the Raspberry Pi because Linux makes a good clock. it supports NTP to set and keep the time accurate and a timezone database. Once it is set up, I shouldn't have to set the time again and it should keep good time. The Pi does has some disadvantages. It isn't well suited to time critical IO but we have a workaround.
I picked the Raspberry Pi 3B+. It is less power than the Pi 4 and will fit the mounting holes provided. It is running headless Raspberry Pi OS Lite.
I got the GRA+AFCH Raspberry Pi code and it was written similar as their Arduino code using WiringPi. Sadly WiringPi has been deprecated. I wrote a daemon in C which can be run as a service and updates the Nixie Tube clock and control the LEDs. In the future, I plan to add a presence detector to turn the Nixie/LEDs on only when standing in front of the clock.
I used a library rpi-ws281x to control the LEDs. This gets around a lot of the timing issues of modulating GPIO for the ws281x smart pixel LEDs. It uses a combination of DMA and Timers. Unfortunately, the board isn't wired to accommodate this so I needed to make a simple hardware change. I use a continuous roll player piano or a simple music box model for this using json as the roll. I use the jsmn json parser to convert the json into a C data structure that is cycled through to control the LEDs.
The Nixie tubes have more forgiving timing and use the built in SPI and memory mapped GPIO. The real time clock (RTC) on the GRA_AFCH board is a DS3231 that the raspberry pi supports natively with some minor modifications.
I wrote this the beginning of 2022. I'll provide links to stuff but your best bet is to search, as with most links become broken in time.
The LEDs do require a minor hardware modification to the top of the raspberry pi adapter board. The rpi-ws281x uses a combination of DMA and PWM timer to provide a jitter free data to the LEDs, unfortunate this only can be done on a few pins which didn't map to the GRA-AFCH board. The GRA-AFCH use a square pad for pin 1 reference consistently. Reading the documentation for the rpi-ws281x, you will see that GPIO12 and GPIO18 are only pins available for PWM0. I used GPIO18 or pin 12 of the 40 pin Pi connector X1 on the adapter board. This pin currently goes to the Up button. You should see a trace from connector AN1 pin 3 to X1 pin 12, you should cut that trace. My suggestion for cutting the trace is to use a sharp xacto knife and pull the knife through the trace with two short parallel cuts about 0.2mm apart from each other perpendicular to the trace. Cut this trace close to X1-12 pad but not that you're going through solder. You need a fairly light touch and not gouge into the FR4 fiberglass while doing this. After several passes, you should have a small rectangular chunk of copper flip come off the board and disappear into the ether. Check the continuity between X1 pin 12 and AN1 pin 3, it should now be open.
You should still have a little stub of trace sticking out of the AN1 pin 3 connector. You can scrape off the solder mask to expose the copper going to AN1 pin 3. If you want to use the button, you can wire this to an unused pin such as X1 pin 22 (GPIO25).
You will need to cut the trace going from connector X1 pin 36 to U2 pin 12. This trace goes under the chip but you want to cut it about 5mm from the X1 pin 36 pad. Check to make sure there is no continuity between U2 pin 12 and X1 pin 36 pad. Next on the trace from the U2 pin 12 pad carefully scrape away the soldermask and tin with solder. That is, flow some solder onto this trace.
You then need to cut a wire that will go from connector X1 pin 12 to this exposed trace. I solder the trace first and lay the wire flat on the board. This is a fragile connection, so I suggest using either Q dope or acrylic conformal coat to stress relief the wire from detaching from this trace. Connect the other end to X1 pin 12.
You could potentially work around cutting the traces but using the button or enabling GPIO16 will make things not work well.
As with any Raspberry Pi OS install, you will need a microSD card, imager, and Raspberry Pi OS image. Just follow the instructions from the site hosting the OS. Once the OS is imaged on the MicroSD, put the MicroSD into a Windows box and open the boot directory. Create an empty text file named ssh (no extension). I usually plug the Pi into Ethernet, let it boot up and see what address the DHCP server assigned it from my router. The Pi will need access to the internet for setting it up.
Once installed, you will need to enable SPI and I2C, they are disabled by default. Start sudo raspi-config and using the arrow keys, select Interface Options <enter> and then SPI and select Yes. Again select Interface Options <enter> and then I2C and select Yes. If you didn't set time zone or localization, they can be set from the Localisation Options and is important to do so.
I use the rpi-ws281x library for controlling the LEDs. It uses a combination of DMA and PWM to reliably control the serial stream to the LEDs. The library needs to be downloaded and built on the pi.
Now install LED library and build using the following:
sudo apt-get -y install gcc make cmake binutils git i2c-tools
cd $HOME
git clone https://github.com/jgarff/rpi_ws281x.git
cd rpi_ws281x
mkdir build
cd build
cmake --D build_SHARED=OFF --D BUILD_TEST=ON ..
cmake --build .
sudo make install
Next install the json parser and nixie daemon code and build:
cd $HOME
sudo git clone https://github.com/zserge/jsmn.git
sudo git clone https://github.com/alkgrove/Pixie-Daemon.git
cd Pixie-Daemon
sudo make
sudo make install
sudo systemctl daemon-reload
Connect the Pi, shield and Nixie board together and power up. Open up a terminal to the pi and try:
i2cdetect -y 1
There should be a single entry at 68, the rest are --. This is the 7 bit hex slave address for the RTC and shows that the pi can see the clock.
Adafruit has a good write up on real time clocks with the raspberry pi. Most of the following is pulled from https://learn.adafruit.com/adding-a-real-time-clock-to-raspberry-pi/set-rtc-time
edit /boot/config.txt with nano:
sudo nano /boot/config.txt
and add the line at the end of the file:
dtoverlay=i2c-rtc,ds3231
Now we need to get rid of the fake-hwclock with the following commands:
sudo apt-get -y remove fake-hwclock
sudo update-rc.d -f fake-hwclock remove
sudo systemctl stop fake-hwclock
sudo systemctl disable fake-hwclock
Next edit the file /lib/udev/hwclock-set and comment out the lines with #'s:
if [ -e /run/systemd/system ] ; then
exit 0
fi
should be
#if [ -e /run/systemd/system ] ; then
# exit 0
#fi
and comment out the lines:
/sbin/hwclock --rtc=$dev --systz --badyear
and
/sbin/hwclock --rtc=$dev --systz
as:
#/sbin/hwclock --rtc=\$dev --systz --badyear
and
#/sbin/hwclock --rtc=$dev --systz
Reboot and test with date:
date
this should produce the right date and time. Next write this to the hwclock with
sudo hwclock -w
sudo hwclock -r
I believe the script you changed does this automatically at some point, this just checks that it works now.
You can further check things with sudo timedatectl status
It should show RTC time with date time which means it's working and it will say n/a if still on fake-hwclock.
You check the NTP servers that are queried for the time with sudo timedatectl show-timesync.
The NTP server is what gets queried over the network to get and set the correct Universal time. Normally these go to a pool of servers such as debian.pool.org. Since my internal network is rather large and some devices aren't allowed on the internet, I use one of my servers as an NTP server and all devices go to it. It in turn, is the only one which updates its clock to a remote NTP server. So I edit the /etc/systemd/timesyncd.conf file and uncomment and change the line NTP=<myserver>.
The LED action is controlled by a json structure and is modeled after a music box or player piano roll. When the daemon starts, it will open the file /usr/local/etc/LEDcolor.json. A default file is installed when pixie-daemon is compiled and installed. There are sample files in the Pixie-Daemon/assets folder.
Each file is made of two objects, "system" and "roll". System has property "level" that will adjust the overall light level from 0 to 100 (percent). "roll" has the property value of an array of objects. These objects have property "step" which can have a value "fast" or "slow", "delay" which is an integer number of milliseconds and "color". Color property value is an array of eight javascript-like RGB colors strings, each string for an LED starting at the left for the first value. The color representation is a string enclosed by quotes and starting with '#' followed by three groups of two hexadecimal numbers each representing 8-bit Red Green Blue Values.
If step is fast, the color will change immediately to the color array and hold that color for delay number of milliseconds. If step is slow, the color will change slowly from the current line to the next line and the transition will take delay number of milliseconds. Delay values for slow need to be in 25millisecond increments.
I would suggest starting the display using the command line especially if trying a new LED color table so you can see any errors. This is done with the command:
sudo /usr/local/bin/pixied
Ctrl-c can be used to exit.
Do the following one time so the daemon starts on boot:
sudo systemctl enable pixied
The nixie clock can be started manually with sudo service pixied start.
Manually stop the daemon with sudo service pixied stop. This may take a minute or more.
To see the daemon status use sudo systemctl status pixied. Originally, this was written with the double forking daemon of old, of which, systemd can do quite odd and disturbing things to your daemon. So I removed it to be a simple style daemon. Good luck with that.