I am a graduate of the University of Pittsburgh at Bradford. I earned a B.S. in Computer Information Systems & Technology with a minor in Digital Graphic Design in Dec. of 2018. My focus is on computer repair and web design. I also earned my extra class amateur radio (ham radio) license in 2008. I am currently working on DSTAR repeaters, helping other hams, get their systems running, and maintaining a local DSTAR repeater (KC3ESS).
I wanted to schedule the DSTAR repeater, that I manage, to reboot automatically every Monday morning. The reason for this is that sometimes Pi-Star stops working and/or freezes up. This typically happens every 2 or 3 weeks of uptime without a reboot. My best guess is that due to the log files not being deleted after rotation, that the Pi software gets “clogged up.” I’ve found settings that are supposed to rotate the logs and only keep a certain number of log files, but those do not appear to work, at least not on our setup.
Since these log files are deleted on every reboot of the Pi, the next best idea in my opinion is to schedule a late-night/early-morning reboot once a week.
I used cron to schedule a reboot. I also use cron to schedule automatic linking and unlinking of reflectors. Pi-Star uses a specialized version of cron that adds a “run as user” option.
Find the Expert Cron Editor Tab
The first step is to log in to your Pi-Star dashboard. This can be accessed by opening a web browser and going to http://pi-star.local/ or http://pi-star/ or the IP address/host name of your Pi-Star repeater or hotspot.
After logging in to your Pi, click on “Configuration” in the upper right of the page.
Next in the upper right of the page click on “Expert”, then on the following page in the bottom row of links on the top of the page click on “System Cron.”
You will see a text box open with a bunch of seemingly cryptic text. Each line is a cron task that is scheduled to happen at a certain time. It should look similar to this:
About halfway down the text box you will see the following line: # m h dom mon dow user command
This line tells us the format of each cron task. The # symbol indicates a comment and tells cron to ignore that line. The “m” indicates “minutes”, “h” indicates hours, “dom” indicates Day of Month, “mon” indicates month, “dow” indicates Day of Week, “user” indicates the user the the command should run as, and “command” is the command you want to run at the given time/day. Refer to the chart below for options for each position in the line.
Enter the minute you want to run the task at or * for any minute.
Enter the hour you want to run the task at or * for any hour.
dom (Day of Month)
Enter the day of the month you want the task to run at or * for any day of the month. Options: 1-31 (date of the month) Example: * = any day of the month Example: 5 = 5th of the Month
Enter the month you want to run a task or * for any month. Options: 1 = January, 2 = February, 12 = December Example: 4 = Run in April Example: 1,6,12 = Run in January, June, & December Example: * = Run any month
dow (Day of Week)
Enter the day of the week you want to run the task or * for any day of the week. Options: 0 or 7 = Sunday, 1 = Monday, 2 = Tuesday, 3 = Wednesday, 4 = Thursday, 5 = Friday, 6 = Saturday Example: 0,3 = run on Sunday and Wednesday Example: 7 = run on Sunday Example: * = run any day
Enter the username of the user that you want to run the command. Options: pi-star, root Example: root
Enter the command to run. This can be a script or a single command or multiple commands. Example: reboot Example: pistar-link unlink && pistar-link ref063_c The above example will unlink the repeater and then link to REF063C.
Normally when you add a cron task it can be anywhere in the cron file, new lines are typically added at the end. In Pi-Star this works too, except that for some reason a line containing the reboot command should be put in as the first cron task in the list, right below the line we see in step 2 under “UNDERSTANDING CRON”.
Note that if you add anything to the end of the file that you must maintain the new blank line at the end of the file. If you’re at the end of the last cron line, press the down arrow on your keyboard. If you see the cursor move down to the blank line, you’re all set. If the cursor doesn’t go down, just press “enter” on the keyboard to add a blank line at the end of the file.
How to Schedule a Reboot
In order to schedule a reboot every Monday at 4:55am, I entered the following line as a cron job. 55 4 * * 1 root reboot >/dev/null 2>&1
Don’t forget to put it at the top of the cron job list, before the first cron job line, but after the line: # m h dom mon dow user command
Now we have a job that says, at 4:55AM every/any month, every/any day of the month, on Monday, run the reboot command as the root user, and do not show output.
The >/dev/null 2>&1 means that whatever text output the command generates won’t be shown or logged. For more info on what this part of the command means, see this forum post on Stack Exchange.
If you use the cron expression generator from Free Formatter, it will not work with Pi-Star, but it will give you the idea of how to write a cron expression. It also lists all the different options and has plenty of great examples of how to use cron.
I’ve been trying to experiment with TinkerCAD to model a 3D printable box for this project. I have the bottom of the case designed with the mounting holes for the Pi. I haven’t been able to figure out how to design the top of the case so that it snaps into place.
Here is a top view of the bottom part of the case.
Here is a top view at an angle.
I have no prototyped this so I can’t even say for sure that the mounting holes are correct, but I believe they are. I did make the holes slightly smaller to allow screws to bite into the plastic.
I enabled DMR last week and spent some time configuring it. This week I had to set the DMR transmit deviation in order to get it to work.
Essentially setting the TX deviation for DMR is the same as how I set the transmit deviation for DSTAR in the beginning. I used a service monitor and checked the deviation level while the repeater was transmitting. It was lower than it should have been, so I increased the level in the expert MMDVMHost editor on the line that said DMR Level. This adjusted the deviation for just DMR, leaving the deviation alone for all other modes.
I also created a box/case for my project out of a large crayon box that I found at WalMart for about $3.
I used a template for the Pi to drill four holes in this box for some #4 screws to mount the Pi and MMDVM duplex. I also put a piece of acrylic between the Pi and this case so that it wouldn’t be pressing against the back of the Pi.
I then cut out a hole for the size of my 3.2in Nextion Display.
I also drilled holes around the display cutout to mount the display in place.
I used plastic from an old ice cream container to create a bezel to go around the display since part of the display doesn’t show anything and is instead used for the touch screen controller/wiring.
I added two external antenna connectors. I bought two male to female jack/panel mount SMA connector extensions for about $6 each and then I added some right angle SMA connectors (male to female) 5 for about $4.
For the external antennas I drilled the holes in the box as far apart as I could and installed the female jack connectors through the hole.
Then I screwed a right angle SMA connector on each jack.
Next, I used a couple right angle SMA connectors on the MMDVM hotspot/repeater board.
Finally, I installed all of the electronics.Here is the finished case.
Last week, I had three problems, two of which I couldn’t fix.
Problems & Solutions
Problem 1 was solved by recompiling the Nextion Driver and reinstalling it by hand.
Problem 2 was that the repeater wasn’t starting up as quickly as it does at home. I thought this was caused by the enterprise WiFi at my university. I’m fairly certain that was the problem. This issue seems to sort itself out, if you’re patient. I’m certain the issue is due to the time it takes the Pi to authenticate with the enterprise WiFi. I did add a button to restart the WiFi from the Nextion display. It is two simple commands.
I added a button to the display’s “System” or utilities screen and made it execute the following commands.
sudo ifdown wlan0 && sudo ifup wlan0
Basically this turns off the wlan0 interface and turns it back on.
Problem 3 was that I couldn’t always access the PiStar dashboard over the WiFi. That problem wasn’t really a problem. Again it had to do with the time the Pi takes to authenticate with the WiFi. I found that if I wait about a minute or two after the display shows the IP address, then go to the displayed IP address in a web browser, the PiStar dashboard appears as it should.
As for the issue with the self-assigned IP address over the ethernet connection, it doesn’t appear to matter. The two devices will communicate with one another given enough time.
A problem I ran into this week was that the repeater board doesn’t always initialize and connect to the software on the raspberry Pi, this is fixed by stopping and starting the mmdvmhost service, which can be done from the Nextion display.
Enable & configure dmr
The first thing I did was enable DMR and I did this from the expert settings for MMDVMHost instead of the main configuration tab. The reason for this is that when you configure from the main tab and click apply changes, you can lose settings you set in the expert MMDVMHost page.
Navigate to the expert editor for MMDVMHost.
Scroll down to DMR.
Your settings should look like this:
What do those settings mean? Enable – On (1) or Off (0) Beacon – Turn on (1) or off (0) beacon or a transmission that happens every so many minutes/hours to tell others your repeater exists. ColorCode – A number for your repeater, typically 1, but may be different. A radio set to a color code of 1 cannot talk to a station with their color code set to 2. SelfOnly – Limit DMR communication to your own callsign only (a Private hotspot) DumpTAData – (1) – Talker Alias data (person’s name/location/callsign) are dropped (0) – Talker Alias data (person’s name/location/callsign) are sent to the RF stations. This can cause issues with some radios, but I set mine to off (0). ModeHang – The number of seconds the repeater should stay listening for DMR over RF after the end of a transmission.
Next scroll down to the DMR Network section of MMDVMHost.
What do these settings mean/do? Enable – Turns on the DMR network/gateway to the internet. Address – The IP Address of the Master Server you’re using. I used Brandmeister 3108 and found its IP address on the Brandmeister website under “Masters.” I believe this is only visible after you’ve logged in with your callsign and Brandmeister password. Port – This is the port on the server you’re connecting too. Leave this as the default. Password – The password to the Master Server. The default for most Masters is “passw0rd”. That’s a zero in place of the letter “o”. Slot1 – This turns on or off slot 1. DMR transmissions are sent in one of two “Time Slots.” Repeaters can receive and carry on two completely separate conversations with one on each time slot. Slot2 – This turns on or off time slot 2. ModeHang – This is the number of seconds the repeater should remain in DMR mode after the end of a network transmission.
Click “Apply Changes”
Add Brandmeister panel
Next I added the Brandmeister control panel to the repeater’s admin dashboard. I followed these instructions.
This is what the Admin Dashboard looks like after adding the Brandmeister control panel. This screenshot was taken before I changed to the US Brandmeister 3108 Server which is why it says “BM United Kingdom” as the DMR Master.
This week, I downloaded a Nextion Display layout created by PD0DIB and modified it to include a system control page and an information page. After trying out the Nextion Driver Installer created by ON7LDS, I could get the screen to display information one time, but after switching pages, the data would disappear. To solve this problem, I looked at the Nextion Driver Installer script and followed most of the steps manually. Doing it this way also allowed me to switch the displayed CPU temperature from celsius to Fahrenheit. This pretty much solved the issues with the display.
In the Nextion Driver Installer Script, I followed this section:
if [ "$ND" = "" ]; then
echo "+ No NextionDriver found, trying to install one."
killall -q -I MMDVMHost
killall -9 -q -I MMDVMHost
if [ "$CHECK" = "PISTAR" ]; then
cp $DIR"/mmdvmhost.service.pistar" /usr/local/sbin/mmdvmhost.service
if [ "$CHECK" = "JESSIE" ]; then
cp $DIR"/mmdvmhost.service.jessie" /lib/systemd/system/mmdvmhost.service
cp $DIR"/mmdvmhost.timer.jessie" /lib/systemd/system/mmdvmhost.timer
cp $DIR"/nextion-helper.service.jessie" /lib/systemd/system/nextion-helper.service
if [ -e /etc/systemd/system/nextion-helper.service ]; then
echo "+ there is already a link /etc/systemd/system/nextion-helper.service"
echo "+ I'll leave it like that."
ln -s /lib/systemd/system/nextion-helper.service /etc/systemd/system/nextion-helper.service
cp NextionDriver $BINDIR
echo "+ Check version :"
echo -e "+ NextionDriver installed\n"
echo -e "+ -----------------------------------------------"
echo -e "+ We will now start the configuration program ...\n"
Basically all I did was the following:
Stop MMDVMHost with “sudo service mmdvmhost stop”
Download the Nextion Driver from github into the /tmp folder
git clone https://github.com/on7lds/NextionDriver.git
Compile the driver by running “make”
Then you should end up with a binary called “NextionDriver”.
This was all done AFTER running NextionDriverInstaller.sh on its own. So, my installation had all the helper files already installed before I ran through these commands.
The hotspot/repeater doesn’t startup right away like it does at home. I’m guessing this is because of the enterprise WiFi at my University. Sometimes the repeater starts right up and works perfectly and other times it does not work.
Problem 2 Solutions
Create a simple script to reset the WiFi connection on the Pi and create a button on the Nextion Display Layout that would allow me to run this script.
Use the same script, but have it run after the Pi is completely booted and add a line to restart the MMDVMHost service.
I could not always access the PiStar dashboard through the ethernet/crossover cable or through the University’s WiFi. Again sometimes I had no issues and other times it would not connect. At first I thought this was due to having both the ethernet and the WiFi running on the Pi, but after removing the ethernet, I had the same issue. I’m growing more suspicious of the enterprise WiFi. As for it not working over the crossover cable, I believe this is due to the fact that the computer is addressing itself with a self-assigned IP address (a 169 address). The problem appears intermittent.
Problem 3 Solutions
Use the solutions for problem 2 as I believe the two problems may be related.
Create a static IP on the Pi and the Computer for the ethernet connection.
Change the PiStar firewall rule for the dashboard from “Private” to “Public.”
After setting up the MMDVM duplex hotspot board, it is necessary to adjust the transmit and receive offsets in the MMDVMHost expert editor section. Basically this corrects the transmit (TX) and receive (RX) frequency of the board, if they’re not on frequency.
I went to a fellow amateur radio operator’s house recently to test my board with his HP 8920A Service Monitor. According to this ham, the service monitor is about 30 years old and cost around $30,000 new. Every 2 years he has it calibrated to NIST standards and it is accurate to +/- 1 Hertz.
The back of the board recommends a TX and RX offset of 500 and then tells you to adjust until the BER or Bit Error Rate is less than 5%. With my friend’s help, I tested the output frequency of the repeater/hotspot board without setting any TX offset and the transmit frequency (FRQ) was about 442.999300Mhz. So I adjusted the TX offset to 500 and retested the transmit frequency. It appears to be getting closer, showing a frequency of about 442.999700Mhz. So I bumped the TX offset up to 800 and that brought the TX frequency up to approximately. 443.000000Mhz, which is right on frequency.
Setting the RX offset is a bit more difficult because there isn’t really a way to test that within Pi-Star. So, I transmitted to the repeater board with my DSTAR handheld and found that I had a bit error rate of 0.1% which really doesn’t need to be fixed.
I set the RX offset equal to the TX offset (800) and that brought the bit error rate down to 0.0%, which is perfect.
I also worked on installing the Nextion Display Driver, however I’m encountering problems with it. The screen layout disconnects from the MMDVMHost software every time the screen changes. I need to work on this a little bit more to solve that problem. I’m thinking the problem is the layout I used. I was testing with a layout from another ham that displays a lot of information and I think the screen has trouble keeping up with the amount of data. I will detail this process in my next post.