A Spectracom "Format 1" time message format emulator. Messages are sent at the top of every second and output to a serial port. This is useful for feeding time data to Spectracom clocks. This script has been tested on various Raspberry Pi's and a Spectracom model 8177 TimeView 400 LED clock. It should work on any UNIX-y platform with any devices that support "Format 1" messages.
I have an obsession with interesting clocks and acquired a Spectracom 8177 TimeView 400 clock from eBay. It was previously installed in a 911 call center. The TimeView 400 can be manually set and seems to keep relatively good time on its own, but it's designed to synchronize with a master clock, such as NetClock models 9183 or 9188. I wanted to keep the clock synchronized witout the use of wiring or external devices. I wanted to use a microcontroller, such as a Raspberry Pi, to keep the clock synchronized with a time (NTP) server.
Two pieces of glue are necessary to make this happen. First, the physical glue -- connecting a Raspberry Pi to the clock. The TimeView 400 uses an RS-485 connection, and the Raspberry Pi's onboard serial ports use TTL (0 - 5 volt) logic levels. A number of converters are readily available on Amazon for this purpose, most for under $10. This made the physical glue pretty much plug and play.
Second, the software glue. The TimeView 400 expects incoming messages at the top of every second that indicate the current date and time. The device supports two protocols, called simply "Format 0" and "Format 1". Thankfully, both formats are fairly well documented in the instruction manuals for the master clock devices. Both formats appeared fairly simple to construct, however Format 1 seemed a bit easier. And thus, this script was born.
First, you'll need a computer. Preferably something cheap and small. The Raspberry Pi with wi-fi is ideal.
Obviously you'll need a clock or other devices that expects the Spectracom Format 1 type messages. They can be found on eBay at varying prices. I've seen them listed for hundreds of dollars, but I was able to acquire mine with a "best offer" price of $55.
You'll also need a converter of some type to convert the serial output of your compute device to the RS-485 connection that your clock (likely) requires. If you are using a Raspberry Pi, or another SBC / microcontroller that uses 3.3v or 5v TTL levels, this is the one I used. It conveniently ships with female jumpers as well, making it easy to interface with a Pi.
https://www.amzn.com/B07B667STP
If your computer outputs RS-232 (i.e. a traditional DB-9 serial port), there are RS-232 to RS-485 readily available as well.
This script was written in and tested with Python 3.7. It uses five modules, four of which are part of the standard library. The fifth, serial, must be installed. On Raspbian, this can be accomplished by running the following:
sudo apt install python3-serial
You will want to make sure your computer is configured to synchronize with an NTP server. Most modern Linux distributions, including Raspbian, use systemd-timesyncd to keep time synchronized. For increased time accuracy, I recommend disabling it and installing chrony instead.
sudo sudo systemctl disable systemd-timesyncd
sudo systemctl stop systemd-timesyncd
sudo apt install chrony
The default chrony configuration should be sufficient, however you are encouraged to research and modify the configuration to your liking.
The Raspberry Pi family of devices are ideal for this purpose, and it's what I'd recommend if you don't already have something else laying around you wish to use. I also recommend the Raspbian operating system. It's lightweight, easy to install, and there's plenty of documentation out there on how to do it without even needing to attach a keyboard / mouse. I recommend using the light version of Raspbian, as you will not need any desktop features.
It's particularly useful that every model includes an on-board serial port. If you are using a Pi device and the Raspbian Linux distribution, you will likely need to make a few configuration changes to configure the on-board serial port. Namely, you will want to turn off Bluetooth (optional but recommended) and configure Linux to not use the serial port as a console. More information can be found here:
https://www.raspberrypi.org/documentation/configuration/uart.md
You will also want to configure Raspbian for the correct time zone. Raspbian defaults to UTC. Since this script outputs the time in local time, your attached clock will display the current time in whichever timezone your Pi is configured for. You can use the raspi-config utility to configure the serial port and set the time zone, as well as configure networking, set the system hostname, and more.
Some Pi variants, notably the Zero and Zero W, do not ship with header pins. If you have one of these variants, you will either need to solder header pins on, or solder wires directly to the correct pins.
- Download the latest copy of the script, place it somewhere convenient, and make it executable:
wget https://raw.githubusercontent.com/mattopia/spectraclock/master/spectraclock.py
sudo mv spectraclock.py /usr/local/bin
sudo chmod 755 /usr/local/bin/spectraclock.py
- Manually run the script in debug mode.
spectraclock.py --debug /dev/ttyAMA0
Change /dev/ttyAMA0 to your appropriate serial device. If you are using a Pi, this should be either /dev/ttyAMA0 or /dev/ttyS0, depending on your configuration.
If everything is properly wired, you should see the clock set itself to match your system's current time within a few seconds. If your clock does not properly synchronize, stop here and review the troubleshooting section. If all is working well, Press Ctrl-C to exit the script.
- Grab a copy of the example systemd unit file and place it in the appropriate location:
wget https://raw.githubusercontent.com/mattopia/spectraclock/master/spectraclock.service
sudo mv spectraclock.service /etc/systemd/system
You may need to edit the spectraclock.service file. Make sure the device name is correct (as tested above). Also, the service definition by default passes an --ntp flag. This enables a feature that checks to see if chrony is synchronized. If you're not using chrony, or if you don't wish to use this feature, remove the --ntp flag.
- Enable and start the service.
sudo systemctl daemon-reload
sudo systemctl enable spectraclock.service
sudo systemctl start spectraclock.service
At this point, you should be all set! Reboot your pi to make sure everything works after a reboot. Find a nice way to mount everything and enjoy!
If the script gives you errors, read the text and use a little deductive reasoning. A few common issues might include using the wrong serial device, missing one or more Python modules, forgetting to make the script executable, etc.
If the script runs, but the time does not sync, first check all of your hardware connections. The RS-485 converter should have an LED that blinks every second. If you don't see this blink, there's probably a connection problem between the converter and the compute device, or you specified the wrong serial device. Try /dev/ttyS0 instead of /dev/ttyAMA0. Also try flipping the send/receive wires, as some RS-485 boards seem to be labeled in reverse of what you'd expect.
If the light is blinking every second, check the wiring between the RS-485 adapter and the clock. It should go straight through, i.e. + to +, - to -, gnd to gnd. Also try flipping the send/receive wires.
If the clock is synchronizing but the seconds digits are flashing, the script is likely sending an unsynchronized flag. Try running the script without --ntp and see if the issue goes away. If it does, make sure you have chrony properly installed and configured. Or, simply exclude the --ntp flag in your systemd unit file.
If the time is synchronizing but it's incorrect, run the script in debug mode and look at the time messages being sent. If they match the clock, check your Pi's system time. The Pi doesn't have an on-board clock and it must synchronize over the Internet. Check your network configuration and your timezone configuration. If you installed chrony, make sure it's configured properly and that you disabled systemd-timesyncd.