Entries posted in February 2018

How we care for our child

Monday, 19 February 2018

This post is a departure from the regular content, which is supposed to be "Debian and Free Software", but has accidentally turned into a hardware blog recently!

Anyway, we have a child who is now about 14 months old. The way that my wife and I care for him seems logical to us, but often amuses local people. So in the spirit of sharing this is what we do:

  • We divide the day into chunks of time.
  • At any given time one of us is solely responsible for him.
    • The other parent might be nearby, and might help a little.
    • But there is always a designated person who will be changing nappies, feeding, and playing at any given point in the day.
  • The end.

So our weekend routine, covering Saturday and Sunday, looks like this:

  • 07:00-08:00: Husband
  • 08:01-13:00: Wife
  • 13:01-17:00: Husband
  • 17:01-18:00: Wife
  • 18:01-19:30: Husband

Our child, Oiva, seems happy enough with this and he sometimes starts walking from one parent to the other at the appropriate time. But the real benefit is that each of us gets some time off - in my case I get "the morning" off, and my wife gets the afternoon off. We can hide in our bedroom, go shopping, eat cake, or do anything we like.

Week-days are similar, but with the caveat that we both have jobs. I take the morning, and the evenings, and in exchange if he wakes up overnight my wife helps him sleep and settle between 8PM-5AM, and if he wakes up later than 5AM I deal with him.

Most of the time our child sleeps through the night, but if he does wake up it tends to be in the 4:30AM/5AM timeframe. I'm "happy" to wake up at 5AM and stay up until I go to work because I'm a morning person and I tend to go to bed early these days.

Day-care is currently a complex process. There are three families with small children, and ourselves. Each day of the week one family hosts all the children, and the baby-sitter arrives there too (all the families live within a few blocks of each other).

All of the parents go to work, leaving one carer in charge of 4 babies for the day, from 08:15-16:15. On the days when we're hosting the children I greet the carer then go to work - on the days the children are at a different families house I take him there in the morning, on my way to work, and then my wife collects him in the evening.

At the moment things are a bit terrible because most of the children have been a bit sick, and the carer too. When a single child is sick it's mostly OK, unless that is the child which is supposed to be host-venue. If that child is sick we have to panic and pick another house for that day.

Unfortunately if the child-carer is sick then everybody is screwed, and one parent has to stay home from each family. I guess this is the downside compared to sending the children to public-daycare.

This is private day-care, Finnish-style. The social-services (kela) will reimburse each family €700/month if you're in such a scheme, and carers are limited to a maximum of 4 children. The net result is that prices are stable, averaging €900-€1000 per-child, per month.

(The €700 is refunded after a month or two, so in real-terms people like us pay €200-€300/month for Monday-Friday day-care. Plus a bit of beaurocracy over deciding which family is hosting, and which parents are providing food. With the size being capped, and the fees being pretty standard the carers earn €3600-€4000/month, which is a good amount. To be a school-teacher you need to be very qualified, but to do this caring is much simpler. It turns out that being an English-speaker can be a bonus too, for some families ;)

Currently our carer has a sick-note for three days, so I'm staying home today, and will likely stay tomorrow too. Then my wife will skip work on Wednesday. (We usually take it in turns but sometimes that can't happen easily.)

But all of this is due to change in the near future, because we've had too many sick days, and both of us have missed too much work.

More news on that in the future, unless I forget.

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Updated my package-repository

Saturday, 17 February 2018

Yesterday I overhauled my Debian package-hosting repository, in response to user-complaints.

I started down the rabit hole due to:

  W: No Hash entry in Release file /.._._Release which is considered strong enough for security purposes

I fixed that by changing my hashes from SHA1 to SHA256 + SHA512, but I was only making a little progress, due to the more serious problem, my repository-signing key was DSA-based and "small". I replaced it with a modern key, then changed how I generate my packages and all is well.

In the past I was generating the Release files manually, via a silly shell-script. Anyway here is my trivial Makefile for making the per-project and per-distribution archive, no doubt it could be improved:

   all: repo

   clean:
       @rm -f InRelease Packages Sources Packages.gz Sources.gz Release Release.gpg

   Packages: $(wildcard *.deb)
       @apt-ftparchive packages . > Packages 2>/dev/null
       @gzip -c Packages > Packages.gz

   Sources: $(wildcard *.tar.gz)
       @apt-ftparchive sources . > Sources 2>/dev/null
       @gzip -c Sources > Sources.gz

   repo: Packages Sources
       @apt-ftparchive release . > Release
       @gpg --yes --clearsign -o InRelease Release
       @gpg --yes -abs -o Release.gpg Release

In conclusion, in the unlikely event you're using my packages please see GPG-instructions. I've also hidden any packages which were solely for Squeeze and Wheezy, but they continue to exist to avoid breaking links.

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Decoding 433Mhz-transmissions with software-defined radio

Sunday, 11 February 2018

This blog-post is a bit of a diversion, and builds upon my previous entry of using 433Mhz radio-transmitters and receivers with Arduino and/or ESP8266 devices.

As mentioned in my post I've recently been overhauling my in-house IoT buttons, and I decided to go down the route of using commercially-available buttons which broadcast signals via radio, rather than using IR, or WiFi. The advantage is that I don't need to build any devices, or worry about 3D-printing a case - the commercially available buttons are cheap, water-proof, portable, and reliable, so why not use them? Ultimately I bought around ten buttons, along with a radio-receiver and radio-transmitter modules for my ESP8266 device. I wrote code to run on my device to receive the transmissions, decode the device-ID, and take different actions based upon the specific button pressed.

In the gap between buying the buttons (read: radio transmitters) and waiting for the transmitter/receiver modules I intended to connect to my ESP8266/arduino device(s) I remembered that I'd previously bought a software-defined-radio receiver, and figured I could use it to receive and react to the transmissions directly upon my PC.

The dongle I'd bought in the past was a simple USB-device which identifies itself as follows when inserted into my desktop:

  [17844333.387774] usb 3-9: New USB device found, idVendor=0bda, idProduct=2838
  [17844333.387777] usb 3-9: New USB device strings: Mfr=1, Product=2, SerialNumber=3
  [17844333.387778] usb 3-9: Product: RTL2838UHIDIR
  [17844333.387778] usb 3-9: Manufacturer: Realtek
  [17844333.387779] usb 3-9: SerialNumber: 00000001

At the time I bought it I wrote a brief blog post, which described tracking aircraft, and I said "I know almost nothing about SDR, except that it can be used to let your computer do stuff with radio."

So my first step was finding some suitable software to listen to the right-frequency and ideally decode the transmissions. A brief search lead me to the following repository:

The RTL_433 project is pretty neat as it allows receiving transmissions and decoding them. Of course it can't decode everything, but it has the ability to recognize a bunch of commonly-used hardware, and when it does it outputs the payload in a useful way, rather than just dumping a bitstream/bytestream.

Once you've got your USB-dongle plugged in, and you've built the project you can start receiving and decoding all discovered broadcasts like so:

  skx@deagol ~$ ./build/src/rtl_433 -U -G
  trying device  0:  Realtek, RTL2838UHIDIR, SN: 00000001
  Found Rafael Micro R820T tuner
  Using device 0: Generic RTL2832U OEM
  Exact sample rate is: 250000.000414 Hz
  Sample rate set to 250000.
  Bit detection level set to 0 (Auto).
  Tuner gain set to Auto.
  Reading samples in async mode...
  Tuned to 433920000 Hz.
  ...

Here we've added flags:

  • -G
    • Enable all decoders. So we're not just listening for traffic at 433Mhz, but we're actively trying to decode the payload of the transmissions.
  • -U
    • Timestamps are in UTC

Leaving this running for a few hours I noted that there are several nearby cars which are transmitting data about their tyre-pressure:

  2018-02-10 11:53:33 :      Schrader       :      TPMS       :      25
  ID:          1B747B0
  Pressure:    2.500 bar
  Temperature: 6 C
  Integrity:   CRC

The second log is from running with "-F json" to cause output to be generated in JSON format:

  {"time" : "2018-02-10 09:51:02",
   "model" : "Toyota",
   "type" : "TPMS",
   "id" : "5e7e0637",
   "code" : "63e6026d",
   "mic" : "CRC"}

In both cases we see "TPMS", and according to wikipedia that is Tyre Pressure Monitoring System. I'm a little shocked to receive this data, unencrypted!

Other events also become visible, when I left the scanner running, which is presumably some kind of temperature-sensor a neighbour has running:

  2018-02-10 13:19:08 : RF-tech
     Id:              0
     Battery:         LOW
     Button:          0
     Temperature:     0.0 C

Anyway I have a bunch of remote-controlled sockets, branded "NEXA", which look like this:

Radio-Controlled Sockets

When I press the remote I can see the transmissions and program my PC to react to them:

  2018-02-11 07:31:20 : Nexa
    House Code:  39920705
    Group:  1
    Channel: 3
    State:   ON
    Unit:    2

In conclusion:

  • SDR can be used to easily sniff & decode cheap and commonly available 433Mhz-based devices.
  • "Modern" cars transmit their tyre-pressure, apparently!
  • My neighbours can probably overhear my button presses.

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Creating an IoT button, the smart way

Friday, 9 February 2018

There are several projects out there designed to create an IoT button:

  • You press a button.
  • Magic happens, and stuff runs on your computer, or is otherwise triggered remotely.

I made my own internet-button, an esp8266-based alarm-button, and recently I've wanted to have a few more dotted around our flat. To recap, the basic way these things work is that you have a device with a button on it.

Once deployed you would press the button, your device wakes up, connects to your WiFi and sends a "message". That message then goes on to trigger some kind of defined action. In my case my button would mute any existing audio-playback, then trigger the launch of an "alarm.mp3" file. In short - if somebody presses the button I would notice.

I wanted a few more doing slightly more complex things in the flat, such as triggering lights and various programs. Unfortunately these buttons are actually relatively heavy-weight, largely because connecting to WiFi demands a reasonable amount of power-draw. Even with deep-sleeping between invocations, driving such a device from battery-power means the life-span is not great. (In my case I cheat, my button is powered by a small phone-charger, which means power isn't a concern, but my "button" is hobbled.)

Ideally what everybody wants is security, simplicity, and availability. Running from batteries, avoiding the need to program WiFi credentials and having a decent form-factor makes an IoT button a lot simpler to sell - you don't need to do complicated setup, and things are nice and neat.

So I wondered is such an impossible dream actually possible, and it turns out that yes, such a device is trivial.

Instead of building WiFi into a bunch of buttons you could you build the smarts into one device, a receiver, connected to your PC via a USB cable - the buttons are very very simple, don't use WiFi, don't need to be programmed, and don't draw a lot of current. How? Radio.

There exist pre-packaged and simple radio-based buttons, such as this one:

button

You press a button and it broadcasts a simple message on 433Mhz. There exist very cheap and reliable 433Mhz recievers which you can connect to an arduino, or ESP8266-based device. Which means you have a different approach:

  • You build a device based upon an Arduino/ESP8266/similar.
  • It listens for 433Mhz transmissions, decodes the device ID.
  • Once it finds something it recognizes it can write to STDOUT (more or less)
  • The host system opens /dev/ttyUSB0 and reads the output
    • Which it can then use to trigger actions.

The net result is you can buy a bunch of buttons, for €5 each and add them to your system. The transmissions are easy to decode, and each button has a unique ID. You don't need to program them with your WiFi credentials, or set them up - except on the host - and because these devices don't do much, they just sleep waiting for a press, make a brief radio-transmission, then go back to sleep, their batteries can last for months.

So that's what I've done. I've written a simple program which decodes the trasmissions and posts to an MQ instance "button-press-a", "button-press-b", etc, and I can react to them uniquely. (In some cases the actions taken depend upon the time of day.)

No code to show here, because it depends upon the precise flavour of button(s) that you buy. But I had fun because some of the remote-controls around my house use the same frequency - and a lot of the cheap "remote-controlled power-switches" use this fequency too. If you transmit as well as receive you can have a decent amount of fun. :)

Of course radio is "broadcast", so somebody nearby could tell I've pressed a button, but as far as security goes there are no obvious IoT-snafus that I think I care about.

In my next post I might even talk about something more interesting - SMS-based things. In Europe (data)-roaming fees have recently been abolished, and anti-monopoly regulations make it "simple" to get your own SIMs made. This means you can buy a bunch of SIMS, stick them in your devices and get cheap data-transfer Europe-wide. There are obvious commercial aspects available if you go down this route, if you can accept the caveat that you need to add a SIM-card to each transmitter and each receiver. If you can a lot of things that become possible, especially when coupled with GPS. Not only do you gain the ability to send messages/events/data, but you can see where it came from, physically/geographically, and that is something that I think has a lot of interesting use-cases.

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