Shallow Thoughts : : Oct

Akkana's Musings on Open Source Computing and Technology, Science, and Nature.

Thu, 26 Oct 2017

Reading an IR Remote on a Raspberry Pi with LIRC

[IR remote with Raspberry Pi Zero W]

Our makerspace got some new Arduino kits that come with a bunch of fun parts I hadn't played with before, including an IR remote and receiver.

The kits are intended for Arduino and there are Arduino libraries to handle it, but I wanted to try it with a Raspberry Pi as well.

It turned out to be much trickier than I expected to read signals from the IR remote in Python on the Pi. There's plenty of discussion online, but most howtos are out of date and don't work, or else they assume you want to use your Pi as a media center and can't be adapted to more general purposes. So here's what I learned.

Install LIRC and enable the drivers on the Pi

The LIRC package reads and decodes IR signals, so start there:

$ sudo apt-get install lirc python-lirc python3-lirc

Then you have to enable the lirc daemon. Assuming the sensor's pin is on the Pi's GPIO 18, edit /boot/config.txt as root, look for this line and uncomment it:

# Uncomment this to enable the lirc-rpi module
dtoverlay=lirc-rpi

Reboot. Then use a program called mode2 to make sure you can read from the remote at all, after first making sure the lirc daemon isn't running:

$ sudo service lirc stop
$ ps aux | grep lirc
$ mode2 -d /dev/lirc0

Press a few keys. If you see a lot of output, you're good. If not, check your wiring.

Set up a lircd.conf

You'll need to make an lircd.conf file mapping the codes the buttons send to symbols like KEY_PLAY. You can do that -- ina somewhat slow and painstaking process -- with irrecord.

First you'll need a list of valid key names. Get that with irrecord -l and you'll probably want to keep that window up so you can search or grep in it. Open another window and run:

$ irrecord -d /dev/lirc0 ~/lircd.conf

I had to repeat the command a couple of times; the first few times it couldn't read anything. But once it's running, then for each key on the remote, first, find the key name that most closely matches what you want the key to do (for instance, if the key is the power button, irrecord -l | grep -i power will suggest KEY_POWER and KEY_POWER2). Type or paste that key name into irrecord -d, then press the key. At the end of this, you should have a ~/lircd.conf.

Some guides say to copy that lircd.conf to /etc/lirc/ andI did, but I'm not sure it matters if you're going to be running your programs as you rather than root.

Then enable the lirc daemon that you stopped back when you were testing with mode2. In /etc/lirc/hardware.conf, START_LIRCMD is commented out, so uncomment it. Then edit /etc/lirc/hardware.conf as specified in alexba.in's "Setting Up LIRC on the RaspberryPi". Now you can start the daemon:

sudo service lirc start
and verify that it's running: ps aux | grep lirc.

Testing with irw

Now it's time to test your lircd.conf:

irw
Press buttons, and hopefully you'll see lines like
0000000000fd8877 01 KEY_2 /home/pi/lircd.conf
0000000000fd08f7 00 KEY_1 /home/pi/lircd.conf
0000000000fd906f 00 KEY_VOLUMEDOWN /home/pi/lircd.conf
0000000000fd906f 01 KEY_VOLUMEDOWN /home/pi/lircd.conf
0000000000fda05f 00 KEY_PLAYPAUSE /home/pi/lircd.conf

If they correspond to the buttons you pressed, your lircd.conf is working.

Reading Button Presses from Python

Now, most tutorials move on to generating a .lircrc file which sets up your machine to execute programs automatically when buttons are pressed, and then you can test with ircat. If you're setting up your Raspberry Pi as a media control center, that's probably what you want (see below for hints if that's your goal). But neither .ircrc nor ircat did anything useful for me, and executing programs is overkill if you just want to read keys from Python.

Python has modules for everything, right? The Raspbian repos have python-lirc, python-pylirc and python3-lirc, and pip has a couple of additional options. But none of the packages I tried actually worked. They all seem to be aimed at setting up media centers and wanted lircrc files without specifying what they need from those files. Even when I set up a .lircrc they didn't work. For instance, in python-lirc, lirc.nextcode() always returned an empty list, [].

I didn't want any of the "execute a program" crap that a .lircrc implies. All I wanted to do was read key symbols one after another -- basically what irw does. So I looked at the irw.c code to see what it did, and it's remarkably simple. It opens a socket and reads from it. So I tried implementing that in Python, and it worked fine: pyirw.py: Read LIRC button input from Python.

While initially debugging, I still saw those

0000000000fda05f 00 KEY_PLAYPAUSE /home/pi/lircd.conf
lines printed on the terminal, but after a reboot they went away, so they might have been an artifact of running irw.

If You Do Want a .lircrc ...

As I mentioned, you don't need a .lircrc just to read keys from the daemon. But if you do want a .lircrc because you're running some sort of media center, I did find two ways of generating one.

There's a bash script called lirc-config-tool floating around that can generate .lircrc files. It's supposed to be included in the lirc package, but for some reason Raspbian's lirc package omits it. You can find and download the bash script witha web search for lirc-config-tool source, and it works fine on Raspbian. It generates a bunch of .lircrc files that correspond to various possible uses of the remote: for instance, you'll get an mplayer.lircrc, a mythtv.lircrc, a vlc.lircrc and so on.

But all those lircrc files lirc-config-tool generates use only small subsets of the keys on my remote, and I wanted one that included everything. So I wrote a quickie script called gen-lircrc.py that takes your lircd.conf as input and generates a simple lircrc containing all the buttons represented there. I wrote it to run a program called "beep" because I was trying to determine if LIRC was doing anything in response to the lircrc (it wasn't); obviously, you should edit the generated .lircrc and change the prog = beep to call your target programs instead.

Once you have a .lircrc, I'm not sure how you get lircd to use it to call those programs. That's left as an exercise for the reader.

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[ 11:21 Oct 26, 2017    More hardware | permalink to this entry | comments ]

Thu, 12 Oct 2017

Letter to the New Mexico Public Education Department on Science Standards

For those who haven't already read about the issue in the national press, New Mexico's Public Education Department (a body appointed by the governor) has a proposal regarding new science standards for all state schools. The proposal starts with the national Next Generation Science Standards but then makes modifications, omitting points like references to evolution and embryological development or the age of the Earth and adding a slew of NM-specific standards that are mostly sociological rather than scientific.

You can read more background in the Mother Jones article, New Mexico Doesn’t Want Your Kids to Know How Old the Earth Is. Or why it’s getting warmer, including links to the proposed standards. Ars Technica also covered it: Proposed New Mexico science standards edit out basic facts.

New Mexico residents have until 5.p.m. next Monday, October 16, to speak out about the proposal. Email comments to rule.feedback@state.nm.us or send snail mail (it must arrive by Monday) to Jamie Gonzales, Policy Division, New Mexico Public Education Department, Room 101, 300 Don Gaspar Avenue, Santa Fe, New Mexico 87501.

A few excellent letters people have already written:

I'm sure they said it better than I can. But every voice counts -- they'll be counting letters! So here's my letter. If you live in New Mexico, please send your own. It doesn't have to be long: the important thing is that you begin by stating your position on the proposed standards.


Members of the PED:

Please reconsider the proposed New Mexico STEM-Ready Science Standards, and instead, adopt the nationwide Next Generation Science Standards (NGSS) for New Mexico.

With New Mexico schools ranking at the bottom in every national education comparison, and with New Mexico hurting for jobs and having trouble attracting technology companies to our state, we need our students learning rigorous, established science.

The NGSS represents the work of people in 26 states, and is being used without change in 18 states already. It's been well vetted, and there are many lesson plans, textbooks, tests and other educational materials available for it.

The New Mexico Legislature supports NGSS: they passed House Bill 211 in 2017 (vetoed by Governor Martinez) requiring adoption of the NGSS. The PED's own Math and Science Advisory Council (MSAC) supports NGSS: they recommended in 2015 that it be adopted. Why has the PED ignored the legislature and its own advisory council?

Using the NGSS without New Mexico changes will save New Mexico money. The NGSS is freely available. Open source textbooks and lesson plans are already available for the NGSS, and more are coming. In contrast, the New Mexico Stem-Ready standards would be unique to New Mexico: not only would we be left out of free nationwide educational materials, but we'd have to pay to develop New Mexico-specific curricula and textbooks that couldn't be used anywhere else, and the resulting textbooks would cost far more than standard texts. Most of this money would go to publishers in other states.

New Mexico consistently ranks at the bottom in educational comparisons. Yet nearly 15% of the PED's proposed stem-ready standards are New Mexico specific standards, taught nowhere else, and will take time away from teaching core science concepts. Where is the evidence that our state standards would be better than what is taught in other states? Who are we to think we can write better standards than a nationwide coalition?

In addition, some of the changes in the proposed NM STEM-Ready Science Standards seem to be motivated by political ideology, not science. Science standards used in our schools should be based on widely accepted scientific principles. Not to mention that the national coverage on this issue is making our state a laughingstock.

Finally, the lack of transparency in the NMSRSS proposal is alarming. Who came up with the proposed NMSRSS standards? Are there any experts in science education that support them? Is there any data to indicate they'd be more effective than the NGSS? Why wasn't the development of the NMSRSS discussed in open PED meetings as required by the Open Meetings Act?

The NGSS are an established, well regarded national standard. Don't shortchange New Mexico students by teaching them watered-down science. Please discard the New Mexico Stem-Ready proposal and adopt the Next Generation Science Standards, without New Mexico-specific changes.

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[ 10:16 Oct 12, 2017    More politics | permalink to this entry | comments ]

Thu, 05 Oct 2017

Tarantula Under Glass, and Micro-Centipedes

Every fall, Dave and I eagerly look for tarantulas. They only show up for a few weeks a year -- that's when the males go out searching for females (the females stay snug in their burrows). In the bay area, there were a few parks where we used to hunt for them: Arastradero, Mt Hamilton, occasionally even Alum Rock. Here in semi-rural New Mexico, our back yard is as good a place to hunt as anywhere else, though we still don't see many: just a couple of them a year.

But this year I didn't even have to go out into the yard. I just looked over from my computer and spotted a tarantula climbing up our glass patio door. I didn't know they could do that!

Unfortunately it got to the top before I had the camera ready, so I didn't get a picture of tarantula belly. Right now he's resting on the sill: [Tarantula, resting after climbing up our glass patio door] I don't think it's very likely he's going to find any females up there. I'm hoping he climbs back down the same way and I can catch a photo then. (Later: nope, he disappeared when I wasn't watching.)

In other invertebrate news: we have a sporadic problem with centipedes here in White Rock. Last week, a seven-inch one dropped from the ceiling onto the kitchen floor while I was making cookies, and it took me a few minutes to chase it down so I could toss it outside.

[Tiny baby centipede] But then a few days later, Dave spotted a couple of these little guys on the patio, and I have to admit they're pretty amazing. Just like the adults only in micro-miniature.

Though it doesn't make me like them any better in the house.

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[ 18:47 Oct 05, 2017    More nature | permalink to this entry | comments ]