For LTX 2023, I built a timing platform centered around Timebeat's Timecard mini.

The time card's GPS modem is used to acquire the precise time using GPS or GNSS satellites, and that time is then displayed on a tiny 1.3" TFT connected through the Raspberry Pi GPIO pins.

A Blinkstick Nano shows different colors and patterns depending on what time it is. It will help me split up time during a live stream into 5 minute segments, so Chris (from Crosstalk Solutions) and I can keep the stream moving along during the busy day at LTX 2023, raising money for the ITDRC.

Watch the video: GPS and a Raspberry Pi over PCI—the new Time Card mini!

Timebeat maintains their own software that integrates PPS output from the U-blox GPS/GNSS module into PTP/PPS inputs and outputs on the Raspberry Pi CM4. The timebeat service is configured via /etc/timebeat/timebeat.yml, and to make sure time is served up through GPS only, you will need to edit that file.

1. Edit the timebeat config file: /etc/timebeat/timebeat.yml
2. Comment out the pps input config example on interface eth0 in the primary_clocks section.
3. Copy the timecard-mini protocol item into the top of the primary_clocks section.
4. Restart the timebeat service: sudo systemctl restart timebeat

If you want to use gpsd instead:

1. Stop and disable the timebeat service: sudo systemctl stop timebeat && sudo systemctl disable timebeat
2. Make sure console=serial0,115200 is not inside the file /boot/cmdline.txt (if so, delete that portion, which sets up ttyS0/serial0 as a UART, then reboot the Pi before proceeding).
3. Install gpsd: sudo apt install -y gpsd
4. Edit the gpsd config file: sudo nano /etc/default/gpsd
5. Change the DEVICES line to: DEVICES="/dev/ttyS0" and save (Ctrl + O, Ctrl + X)
6. Restart the gpsd service: sudo systemctl restart gpsd
7. Run gpsmon to make sure the GPS module is found—it should show up in the DEVICES output, and after a while, once GPS satellites are found, you should see TODO.

Once gpsd is running and configured, you need to set the system to use the GPS module as a time source. The GPS module needs to output PPS (Pulse Per Second) for this to work, and luckily, the U-blox should. However, it won't until the receiver gets a GPS fix (and this can take a while sometimes, especially if you don't have a clear view of the sky).

You can stop gpsd and run ppscheck /dev/ttyS0 to monitor for PPS's, or just wait (and use gpsmon while gpsd is running—it should also show PPS's).

Setting up NTP or Chrony to use gpsd for PPS input is not covered here. I'll do that at some point in the future.

For quick visual indication of how much time remains in 5-minute segments during an LTX livestream, I have a Blinkstick Nano plugged into the USB-A port on the Timecard mini.

(Note: I used a PiTray mini for the eeprom flashing. Procedures to program the CM4 eeprom using usbboot vary by CM4 IO board model, but typically you would disable the eMMC Boot option, whether via dip switch or jumper.)

1. Plug the CM4 into a PiTray mini.
2. Ensure the eMMC Boot switch is 'OFF'
3. Plug the PiTray mini into your computer.
4. Follow these steps to flash the eeprom of the CM4 using usbboot.
5. When it comes time to edit the boot.conf file, add the following line to the end of the file, and save it, before running ./update-pieeprom.sh.
6. After the update is complete, unplug the CM4 and plug it back into the Timecard mini.

The Pypi blickstick package has a few bugs currently, but you will still use it for the Python script that will display time on the LED.

1. Install pyusb: sudo pip3 install pyusb

2. Install blinkstick: sudo pip3 install blinkstick

3. Copy the blinkstick/ directory into /opt

4. Create a systemd unit for blinktime.py: sudo nano /lib/systemd/system/blinktime.service

5. Inside, put:

   [Unit]
   Description=blinktime
   Wants=network.target
   After=network.target
    
   [Service]
   Type=simple
   ExecStart=/usr/bin/python3 blinktime.py
   WorkingDirectory=/opt/blinkstick
   Restart=always
    
   [Install]
   WantedBy=multi-user.target
   

6. Reload systemctl: sudo systemctl daemon-reload

7. Enable the service: sudo systemctl enable blinktime.service

8. Start the service: sudo systemctl start blinktime

If you connect an Adafruit mini PiTFT HAT to the Rasbperry Pi GPIO header, you can display the current time and GPS status on a handy little screen.

Hardware-wise, to clear the sandwich stack of all the Time Card boards, I had to purchase a GPIO stacking female header kit.

For software setup, you need to copy over the wopr code, then set it to run on boot. And yes, wopr is a reference to the game countdown display on the War Games WOPR computer.

sudo apt install -y python3-pip fonts-dejavu python3-pil python3-numpy
sudo pip3 install --upgrade adafruit-python-shell
wget https://raw.githubusercontent.com/adafruit/Raspberry-Pi-Installer-Scripts/master/raspi-blinka.py
sudo python3 raspi-blinka.py

Reboot, then:

sudo pip3 install adafruit-circuitpython-rgb-display
sudo pip3 install --upgrade --force-reinstall spidev

This script was tested along with Timebeat's Multi-constellation GPS / GNSS module, specifically the U-blox LEA-M8F variant.

There is a script that checks on the GPS status and writes to a file in /tmp/gps-status either 'A' (GPS is locked) or 'V' (GPS is not locked / acquiring).

This script is used by the WOPR script to display GPS status information.

1. Copy the gps/ directory into /opt on the Raspberry Pi.

2. Create a systemd unit for gpslock-timebeat.py: sudo nano /lib/systemd/system/gpslock.service

3. Inside, put:

   [Unit]
   Description=gpslock
   Wants=network.target
   After=network.target
    
   [Service]
   Type=simple
   ExecStart=/usr/bin/python3 gpslock-timebeat.py
   WorkingDirectory=/opt/gps
   Restart=always
    
   [Install]
   WantedBy=multi-user.target
   

4. Reload systemctl: sudo systemctl daemon-reload

5. Enable the service: sudo systemctl enable gpslock.service

6. Start the service: sudo systemctl start gpslock

If you are not running Timebeat, you can directly access the serial port to get GPS data using the gpslock.py script—just copy that script into the /opt/gps folder, and update the ExecStart statement to point to it.

1. Copy the wopr/ directory into /opt on the Rasbperry Pi.

2. Create a systemd unit for wopr.py: sudo nano /lib/systemd/system/wopr.service

3. Inside, put:

   [Unit]
   Description=WOPR
   Wants=network.target
   After=network.target
    
   [Service]
   Type=simple
   ExecStart=/usr/bin/python3 wopr.py
   WorkingDirectory=/opt/wopr
   Restart=always
    
   [Install]
   WantedBy=multi-user.target
   

4. Reload systemctl: sudo systemctl daemon-reload

5. Enable the service: sudo systemctl enable wopr.service

6. Start the service: sudo systemctl start wopr

MIT

This project was built in 2023 for LTX Expo by Jeff Geerling.