Steps and notes for installing a GPS-sourced local NTP server and HamClock.
- Raspberry Pi 4
- Raspberry Pi PoE+ HAT
- Adafruit Ultimate GPS HAT
- Raspberry Pi Foundation 7" Display
- SmartiPi Touch Pro case
- RAM Mount VESA Plate
- RAM Mount short arm
- RAM Mount round plate with ball
I power it with a PoE HAT since as a network time server it's always running, and I didn't have spare power outlets nearby.
I tried running Raspberry Pi OS bullseye, but I can't seem to get it to boot when using the PoE+ HAT. Without the HAT it boots, so one day I may try a different PoE HAT to see if that works. In the meantime I'm using Raspberry Pi OS (Legacy) with desktop.
Don't connect the case's USB-C passthrough cable to the Raspberry Pi board when using the PoE+ HAT; the HAT only expects to get power from the Ethernet jack and not from the Pi.
The SmartiPi case has mounting brackets side-by-side. I mounted the Pi with the PoE HAT on the on the right, and the GPS HAT on the left. I tried using a ribbon cable to connect the two, but there wasn't enough clearance on the PoE HAT for the ribbon cable to connect, so I made my own using jumper cables and wire housing blocks.
For the count-down timer I wired the button like the HamClock user guide suggests (pin 37), but only the green LED (pins 17 and 35) so I don't have a red LED flashing at me when I'm not using the radio. I figure If I don't have a green light, I need to restate my callsign.
I also wired up the satellite alarm (pin 38).
I also added a button to turn the screen on/off on demand (pin 18). The breadboard of the GPS HAT is a great place to solder connections for a capacitor to prevent debouncing. See screenblanker for details.
The case has VESA mounting points on the back, so I used the listed RAM Mount accessories to mount the case to my desk so it floats overhead for easy reach.
cd ~/Documents &&
git clone https://github.com/gfitzp/screenblanker.git &&
sudo cp screenblanker/screenblanker.service /etc/systemd/system/ &&
sudo systemctl daemon-reload &&
sudo systemctl enable screenblanker.service &&
sudo reboot
Add screenblanker schedule to crontab (turns screen on at 9 AM, turns screen off at 11 PM).
0 9 * * * /usr/bin/python3 /home/pi/Documents/screenblanker/screenblanker.py noblank >/dev/null 2>&1
0 23 * * * /usr/bin/python3 /home/pi/Documents/screenblanker/screenblanker.py blank >/dev/null 2>&1
Don't forget to disable the Raspberry Pi's built-in screenblanker!
The HamClock has a screenblanking scheduler too, but I wanted the option to easily turn the screen off/on manually and on a schedule.
sudo raspi-config
3 Interface Options > P6 Serial Port
I believe these set the CPU to a fixed frequency to help with keeping accurate time.
echo $(cat /boot/cmdline.txt) "nohz=off" | sudo tee /boot/cmdline.txt &&
echo "performance" | sudo tee /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
sudo apt-get -y update &&
sudo apt-get -y full-upgrade &&
sudo apt -y auto-remove
sudo apt-get -y install gpsd gpsd-clients python-gps pps-tools
Configure the GPS.
sudo tee /etc/default/gpsd > /dev/null <<EOT
# Default settings for the gpsd init script and the hotplug wrapper.
# Start the gpsd daemon automatically at boot time
START_DAEMON="true"
# Use USB hotplugging to add new USB devices automatically to the daemon
USBAUTO="false"
# Devices gpsd should collect to at boot time.
# They need to be read/writeable, either by user gpsd or the group dialout.
DEVICES="/dev/ttyAMA0 /dev/pps0"
# Other options you want to pass to gpsd
GPSD_OPTIONS="-n"
EOT
Enable PPS output on the GPIO pin.
echo "pps-gpio" | sudo tee -a /etc/modules
Enable the serial port, disable Bluetooth for system performance, and customize the PoE hat fan speed temperature triggers. Also turn off the ethernet jack lights as it's distracting when I'm trying to sleep! :P
sudo tee -a /boot/config.txt > /dev/null <<EOT
# Custom configuration starts here
# Enable serial port
enable_uart=1
# Disable bluetooth
dtoverlay=disable-bt
# Enable the PPS signal on GPIO pin
dtoverlay=pps-gpio,gpiopin=4
# PoE Hat Fan Speeds
dtparam=poe_fan_temp0=70000
dtparam=poe_fan_temp0_hyst=2000
dtparam=poe_fan_temp1=80000
dtparam=poe_fan_temp1_hyst=2000
dtparam=poe_fan_temp2=90000
dtparam=poe_fan_temp2_hyst=2000
dtparam=poe_fan_temp3=95000
dtparam=poe_fan_temp3_hyst=5000
[pi4]
# Disable the PWR LED
dtparam=pwr_led_trigger=none
dtparam=pwr_led_activelow=off
# Disable the Activity LED
dtparam=act_led_trigger=none
dtparam=act_led_activelow=off
# Disable ethernet port LEDs
dtparam=eth_led0=4
dtparam=eth_led1=4
EOT
chronyd will take the place of ntp.
sudo systemctl disable ntp
sudo apt-get -y install chrony
sudo tee /etc/chrony/chrony.conf > /dev/null <<EOT
# Welcome to the chrony configuration file. See chrony.conf(5) for more
# information about usuable directives.
#pool 2.debian.pool.ntp.org iburst
# This directive specify the location of the file containing ID/key pairs for
# NTP authentication.
keyfile /etc/chrony/chrony.keys
# This directive specify the file into which chronyd will store the rate
# information.
driftfile /var/lib/chrony/chrony.drift
# Uncomment the following line to turn logging on.
#log tracking measurements statistics
# Log files location.
#logdir /var/log/chrony
# Stop bad estimates upsetting machine clock.
maxupdateskew 100.0
# This directive enables kernel synchronisation (every 11 minutes) of the
# real-time clock. Note that it can’t be used along with the 'rtcfile' directive.
rtcsync
# Step the system clock instead of slewing it if the adjustment is larger than
# one second, but only in the first three clock updates.
makestep 1 3
# Custom chrony configuration
# These servers are used when the GPS isn't working for some reason.
# iburst is used on all servers when initially starting to speed up the first clock update
# Poll the local server more frequently (minpoll 3 = 2^3 = at least every 8 seconds)
# Poll remote servers at most every 32 seconds (maxpoll 5 = 2^5 = 32)
# Why? see https://gpsd.gitlab.io/gpsd/gpsd-time-service-howto.html#_arp_is_the_sound_of_your_server_choking
server 192.168.1.1 iburst minpoll 3 maxpoll 5
pool time.apple.com iburst maxpoll 5
pool time.google.com iburst maxpoll 5
pool time.nist.gov iburst maxpoll 5
pool us.pool.ntp.org iburst maxpoll 5
refclock PPS /dev/pps0 refid PPS precision 1e-7 lock NMEA
refclock SHM 0 refid NMEA precision 1e-1 offset 0.541 delay 0.2
# Allow devices to use chrony as their NTP source
allow 127.0.0.1
allow 192.168.0.0/16
allow 100.64.0.0/10
# Enable logging
log tracking measurements statistics
logdir /var/log/chrony
logbanner 21
EOT
Sometimes it seems chrony doesn't know about the GPS service until gpsmon is run. Append gpspipe to the rc.local startup file and have it output one NMEA line before it exits.
sed -i '$ s/exit 0/gpspipe -r -n 1 \&/g' /etc/rc.local ; echo exit 0 >> /etc/rc.local
You may need to experiment in order to determine your particular offset and delay values.
sudo systemctl restart chronyd &&
watch chronyc tracking
chronyc sources -v
cd /var/logs/chrony
HamClock by Elwood Downey, WB0OEW
curl -O http://www.clearskyinstitute.com/ham/HamClock/install-hc-rpi &&
chmod u+x install-hc-rpi &&
./install-hc-rpi
Manually enter in the latitude / longitude from cgps into the HamClock setup screen.
It seems if gpsd is enabled in the HamClock, it uses gpsd for both GPS positioning and timekeeping. However, I don't believe gpsd uses the PPS output, so we get more accurate time from our local NTP server; we'll use that instead.
Set "NTP?" on Page 2 of the HamClock setup screens to 127.0.0.1; we specifically allow the local machine to poll chrony for the network time in the chrony.conf file.