Tag Archives: Airmar

The Power of Raspberry Pi–MythTV tweaks and techniques

Posted on by under anchoring, Geekery, living aboard, misc, Systems, Weather

This post continues my previous ramblings about using the Raspberry Pi aboard the boat.  To start this story at the very beginning, go to this post. To go to the previous post in this series, go here.

Screenshot of MythWeb running on Raspberry Pi 2

Now to discuss some lessons we have learned about using our RPI-2 with MythTV aboard Schooner Mahdee to record over-the-air TV broadcasts for later viewing: Why record when so much is available instantly over the Internet?  Four reasons:

  • we are often anchored where Internet access is unavailable, or the speed is too slow to stream video;
  • we pay for high speed (4G) access per gigabyte;
  • broadcast HDTV provides an effectively free source of additional bandwidth and the HDTV programming is often many times much higher resolution than via Internet streaming;
  • those shows can be saved on a hard drive for later viewing anywhere and anytime.

Stunningly beautiful full 1080 HDTV programming is often broadcast and can be saved for later viewing on a big vibrant HD computer monitor–even in places with no Internet at all.  Those very high resolution shows consume around 5GB per hour.  If using our 4G hotspot, at that rate, our entire monthly Internet bandwidth for work and pleasure is equivalent to a couple of HDTV movies.  By comparison, in some locations, we can record HDTV shows around the clock for free–an incredible deal!  In practice, each 24 hours of saved H-264 encoded HDTV recordings exceeds our total Internet bandwidth usage for the entire month. Our only cost is for the hard drives and each $150 hard drive can save thousands of shows and take up less space on the boat than a small paperback novel.  So, even when we could stream videos over the Internet, we rarely do.

Since we obviously travel a lot, our settings for MythTV are not set and forget–in contrast to more stationary users.  We use Antenna Web in each new location to determine where HDTV transmitters are relative to us and how well we can expect to receive different stations.  We have both an omni-directional and a directional gain antenna to choose from.  Spinning around on a single anchor makes the directional antenna unusable, but if the boat is fixed in orientation with multiple anchors or shore-tie, we can use it to increase reception of more distant HDTV stations.  Sometimes we can get great reception with the antenna below decks in a stealth mode.  For more challenging stations, reception may require an antenna be raised on a flag halyard–not so stealthy.

We have an inexpensive account at Schedules Direct which interfaces very well with MythTV.  With an Internet connection, we generally upload new schedule data every day or two.  There is limited (just the next 12 hours) program schedule data provided for free by the stations themselves on the transmitter frequency using EIT, but scheduling works best with longer range data and Schedules Direct provides about two weeks of scheduling. That data also includes lists of actors and other credits as well as descriptive information which we retain with our recordings and in a separate custom Ruby-on-Rails (RoR) web interface and database.

Schedules Direct also allows us to have four different locations in our profile.  Thus, we have one for each major city area we typically visit.  In those profiles, we can remove stations we do not want–such as those without English language audio–and our custom settings will persist until our next visit to that area.  I am constantly amazed at the number of over-the-air broadcast stations we can receive even when we are far from a metropolitan area.

With our large MythTV database of over 10,000 previously recorded shows, nearly 100 channels of available broadcast programs in many locations, and large number of rules and priorities about what we want to record, it can take several minutes after starting the MythTV back-end for it to figure out what to record. During that time, the MythTV front-end and MythWeb browser interface running on the RPI-2 will will show no scheduled recordings. Whenever possible, I use the command-line mythtv-status to see what is in the recording queue rather than running the more resource-intensive front-end. Even mythtv-status can take several minutes to complete and will show that nothing will be recorded until all of the data has been parsed and prioritized by the MythTV back-end.  Loading new schedule data from Schedules Direct can take nearly 20 minutes to process on our–admittedly overloaded–RPI-2. Sort of like sailing tack to tack to get to one’s ultimate destination, patience is required and one can not expect a newly added show to be put into the recording queue right away. I plan for the RPI-2 to take up to five minutes before a new recording is reflected in the queue.

With an Internet connection, MythTV gets program meta data for each recording so that we have images of cover art–which makes the front-end display nicer.  MythTV can also flag commercials so that they can be easily skipped during replay or even removed from the file entirely.  Commercial detection is very resource intensive, so we set MythTV on the RPI-2 to not do any commercial detection on the recordings. With this setup, the RPI-2 is also very useful as a desktop computer for me to browse the Internet using Firefox/Iceweasel, read and write email and other miscellaneous things all while displaying current weather data and monitoring anchor holding.

One glitch that I have encountered is that the MythTV startup script does not always work in Debian Jessie due to incompatibility with SystemD. The symptom is that the startup script completes with no errors, but the back-end is not running–starting and restarting MythTV using has no effect. The problem seems to be related to the init-functions command. Adding the following just before that call in /etc/init.d/mythtv-backend as follows helped:

_SYSTEMCTL_SKIP_REDIRECT=true
. /lib/lsb/init-functions

Then that fix failed so I am now manually starting MythTV using the old InitV command:

/etc/init.d/mythtv-backend start

It is also good to ensure that MythTV is not running before starting it and to make sure there is no file named /var/run/mythtv/mythbackend.pid. First kill hung processes and then check for the pid file and delete it if necessary before staring MythTV using the above command. Since I rarely reboot the RPI-2, manually starting MythTV works fine and the InitV command is trouble free.

Another glitch is that the HD HomeRun recordings sometimes fail leaving MythTV thinking the recording is still happening. After upgrading the HomeRun to the latest firmware, this situation happens less often. Still, every few days I need to stop MythTV and wait for all the threads to be killed and then restart MythTV.

Next, I will cover some system-wide optimizations that we have made that make MythTV more reliable given the highly loaded RPI2 we run it on.

Addendum: this conversation continues on our technology-focused website Windward Ho!

The Power of Raspberry Pi–rethinking and restructuring to do even more with less

Posted on by under anchoring, living aboard, Systems, Weather

To start this story at the very beginning, go to this post. To go to the previous post in this series, go here. As it may be clear from the discussion so far, I have a tendency to increasingly add more requirements and functionality to my Raspberry Pi (and/or the newer version 2 RPI-2) computer until it cries “uncle”–or more often than not, just quietly dies under the extreme load. This post is about adding more functionality, but by being smarter, avoiding the dying part–at least for now.

myth tv running on raspberry pi
Every traditional boatwright needs to watch the Woodwright’s Shop for inspiration.

One of our luxurious activities when paying to be at a marina with shore power is to run my Shuttle small-form-factor (SFF) computer with its Intel i7 CPU and lots of RAM and lots of storage space. When it is running, it records over-the-air–using an antenna–HDTV movies and shows according to various rules we have programmed. Those shows are re-encoded by the Shuttle computer in a very efficient format to make the files smaller–1/3 to 1/5 original size–and then saved to a hard drive for later viewing–like when storm-bound in a remote bay somewhere in Alaska.

Our time in marinas is limited and the Shuttle requires too much power to run just for recording shows (producing non-shore power electricity is very expensive) and the movie recording program is way too demanding for a regular RPI. But now I thought maybe, just maybe, the new RPI-2 could record TV programs–of course I really mean do that in addition to all the other stuff the RPI-2 already does.

The program we use to record over-the-air shows is called MythTV. I have a love-hate relationship with MythTV, but we have been using it for about 10 years and it keeps track of every show ever recorded by us so that it doesn’t re-record something we already have on a hard disk or DVD or CD-ROM somewhere on Mahdee or in storage. The challenge for us is that the database for MythTV has a huge number of recordings (way over 10 thousand) to keep track of and the scheduler needs to sort through all of our rules (which are numerous and have evolved from our refinements over those same 10 years) and compare rule-matching scheduled showings to already recorded shows and determine which shows to actually record when so as to optimize the recordings. I had my doubts that even the RPI-2 would be capable–let alone doing that task while also doing the really important stuff like keeping track of the weather and how well the anchor is holding–after all, we do have to keep our priorities straight.

To make the RPI-2 able to record TV movies we had to make some changes.

1. We bought a network HDTV tuner (HD HomeRun Extend HDTC-2US) that has a built-in transcoder that re-encodes the movies in a more space-efficient format (H-264) on-the-fly. This removes the requirement for the RPI-2 to re-encode the recordings–which it couldn’t do anyway–and keeps the file sizes reasonable. In addition, H-264 is an open standard whereas the original inefficient proprietary format used in over-the-air transmissions requires one to buy a MPEG license before the RPI-2 can perform hardware decoding for viewing. So not only is the output of the HD HomeRun more space efficient, it also uses an open standard that doesn’t require the purchase of a license. The HD HomeRun even runs on 12V DC which is nice. So we installed a 60W regulated 12V DC power supply on Mahdee to use the HD HomeRun off a 12V DC battery.

2. The other change was to continually power up the Linksys Wifi router. The Linksys is also powered by 12V DC–so it can use the same newly installed regulated power supply as the HD HomeRun. Earlier, we tried to make the RPI be Mahdee’s Wifi access point in order to save the power required to run the Linksys. Running the Linksys offloads the Wifi access point functions but more importantly, also provides a needed Ethernet hub. The hub makes is possible for the HD HomeRun tuner to be available to the RPI-2, as well as to my Shuttle computer, all over fast Ethernet rather than Wifi. Further, we decided that we could also keep running the old RPI and use it via Ethernet to offload some functions from the new RPI-2–such as internet gateway, firewall, GPS server, network time server using GPS, secondary/backup anchor position alarm, Scrabble game server (oh–didn’t I mention that requirement), as well as that coveted contact and calendar schedule web server.

The net result is that, even though we now have two Raspberry Pi’s running (an RPI and an RPI-2) along with a network TV tuner and a Linksys router (the latter two alone adding 24 amp-hours a day to our afloat battery usage), our electric power usage is less than half of what it was at the dock with the Shuttle computer running. We are now getting recordings and a practical, fun to use computer that is available 24-7 even while at anchor. All that while logging weather and boat data and monitoring that important data with alarms to keep us safe. The RPI-2 has been exceptionally reliable with our previous and current up-time exceeding three weeks since the last intentional reboot.

When passage making, we can turn off the network TV tuner, Linksys router and the RPI to reduce power usage without loosing any important functionality–e.g. don’t really need our contact server in the middle of the ocean. And with no TV tuner, we can turn off MythTV and have plenty of CPU capability on the RPI-2 to run the OpenCPN chart plotter which can use either the weather/boat data pseudo serial port on the RPI-2 for GPS data or the GPS data on the RPI if it hasn’t been secured to save power. With this nice flexible and stable setup, I have to keep telling myself not to add anything new. Unfortunately, I know that it is only a matter of time before I come up with new ideas of things/tasks/programs to add to the RPI-2. With any luck, a new more capable RPI-3 will come out before I completely overload the RPI-2. Right now, however, I am really happy with both my RPI and RPI-2.  Next I will cover some tips for running MythTV on the RPI-2 without impacting all the other stuff the RPI-2 needs to do.

The Power of Raspberry Pi: over reaching and hitting the wall

Posted on by under anchoring, living aboard, misc, Systems, Weather

For background, see the previous post here. At this point, the Raspberry Pi (RPI) has proven itself aboard Schooner Mahdee by reliably logging data from our Airmar weather station plus other boat data and displaying that data on an HDMI monitor, as well as monitoring that data and sounding alarms as required. We built in the capability for more than one computer to read the Airmar weather/boat data from the RPI network port at the same time. To realize that potential, we needed a Wifi access point. A USB Wifi dongle, supporting the access point protocol, with the right software (in our case HostAPD) turned the RPI into an access point for all Mahdee users. A good access point provides some basic network services that were set up on the RPI–such as IP address assignment DHCP server–and is a domain name server (we used Bind9 server) for all the Wifi-connected computers aboard the boat.

Raspberry Pi and Cat

Further adding to the roles for the RPI, I wanted to be able to read email without turning on any other computer, so we needed to set up internet access on the RPI. We set up the RPI to use either a Sprint phone with a data tethering plan using PPP or our Verizon Wifi hotspot using a second USB Wifi dongle. Since Brenda’s Windows 8 machine can’t tether directly to the Sprint phone, we decided to make the RPI Mahdee’s internet gateway that can be switched between either Sprint or Verizon. That also meant a better firewall setup for the RPI.

The RPI doesn’t have a hardware clock (by design it would rely on an internet connection to set the time on boot), so when we rebooted the RPI, sans-internet, in the middle of nowhere in Alaska, the data logger had the wrong time stamps. To fix that, we setup a USB puck GPS as a time source for the RPI. This meant also running a GPS position server on the RPI which is then available on a network port of the RPI for other computers aboard Mahdee. The fast high resolution GPS data was also setup to be used by a Python anchor watch and position alarm which I’d previously written for the Nokia N810. The sound system on the RPI is not very good nor very loud even with our USB powered amplified speakers.  For the alarms we setup a piezo-electric buzzer which is energized by a RPI GPIO port so that we can hear alarms anywhere aboard the boat. The RPI also uses GPS time stamps to provide a network time basis for other computers aboard.

With the 2TB Passport hard drive attached to the RPI, it only made sense to put a copy of our public file archive on it and thereby make it available to us 24-7. The public file archive includes repair manuals in PDF form for most boat systems (nice to have in an emergency), all of our photos as well as digital books and magazines (nice for passage entertainment). This nicety meant putting PDF and e-book readers on the RPI. Then, to enable access to those files from Windows computers, we setup a Samba server which also requires a network time server. Fortunately we already had the GPS-based network time server on the RPI.

To enable us to read our email when there is no internet connection available, we setup the RPI with OfflineIMAP to sync mail from our main email server (an off-boat/shore-based virtual private server) whenever we have internet access. I read email using Mutt which can run in a terminal on the RPI. Brenda likes to access email using SquirrelMail webmail via her computer’s web browser, so we added an Apache2 web server to the RPI along with Squirrel Mail and an IMAP server.

In among the public archive data is our music collection, so we setup RPI as a network music player. On those long passages, we thought it would be nice to listen to music, but this is where things start to break down. The poor, now very overloaded, RPI just couldn’t make the music sound even decent. I also setup my Bluetooth stereo headset on RPI, but that was even worse than listening to broken up music through the speakers.

Many boaters want their RPI to run a navigation program like OpenCPN. I had managed to compile a version of OpenCPN on our first RPI, but running OpenCPN required all the resources of the RPI and I was not willing to forego all the other important roles our RPI was needed for–simply to use OpenCPN as a backup chart plotter.  Our real chart plotter is used to display radar and chart data including charts for other countries without free official charts (like Canada). Not needing to run OpenCPN helped a little with our overloaded RPI situation.

From the RPI GUI interface, I found web browsing to be very slow and unproductive. I could get email and read it using Mutt just fine, but there was other trouble lurking. Brenda informed me that basic web access from her computer through the RPI Wifi access point was way too slow. I tried it using my main computer and had trouble too. I had had hopes–fantasies perhaps–that RPI would also run a contact and calendar web service. Most people would just use Google for this, but we are often not near internet access and besides, who really wants to trust the big guys with all of your sensitive contacts and scheduling. But, it was not to be–at least not yet.  Stay tuned for the next installment in this series of posts about the RPI and how we turned the corner towards success.

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