Gyro Wheel Battery Pack

Several years ago I bought a Gyro Wheel for my daughter, who probably couldn't even walk at the time. The idea seemed really good; a heavy cast-iron wheel is spun up and the angular momentum keeps the new-rider upright while they learn to ride.

I don't suppose it revolutionised bike-riding, as it seems that the company has disappeared. Now my daughter can reach the pedals, when I finally dug it out the other day it was sad to find it wouldn't charge. Googling seems to show that it's a fairly common problem.

After pulling it apart, I found that it was fairly straight-forward to replace the battery-pack. Getting in requires a torx screwdriver but is otherwise straight-forward.

The battery looks like a bit of a custom job, with two-halves of a 9.6V battery-pack split into two. You won't be able to buy anything that directly replaces this, but you should be able to find individual AA-sized NiMH rechargable batteries with welded-tabs that you can use to create a new battery-pack (don't buy batteries without tabs and try to solder directly onto the battery terminals, it won't work). Unwrap the plastic from the existing packs and just follow the polarity; if you carefully de-solder the existing wires you can save yourself a lot of work making new ones. Wrap it up securely and put everything back together.

Below are some photos just to give you an idea of what to expect.

Tenvis IP391W meta-page

Recently I purchased a Tenvis IP391W-HD camera.

I would be unlikely to recommend it. The price is certainly right and the picture quality is quite good. The Android and iPhone apps do work to watch the stream live.

However, the interface is terrible and almost useless without Internet Explorer. There is a RTSP stream (rtsp://admin:password@ip) which VLC can seem to handle, but not mplayer. The recording format (.h264) is not viewable by VLC or mplayer and all I could find is a Windows .exe to convert them to an .avi.

The motion detection gets troubled by the dark. It would really only be useful for something permanently well-lit. It did send me emails via gmail.

I have got it recording to a NFS server, but I don't have a lot of confidence in the reliability of it. I think I have it configured to record in 3600-second blocks (given the interface, it's hard to tell if I've set it up to the network, or to the internal flash, etc), but it seems to intersperse 60 minute recordings with random small recordings. Given the whole idea of a security camera is to record the unexpected, you want a lot of confidence you're actually recording, which you don't get with this. You can see below it recorded 3 hour blocks, then started going a little crazy...

-rw-r--r-- 1 nobody nogroup  69M Mar 11 01:25 0-003035.v264
-rw-r--r-- 1 nobody nogroup  69M Mar 11 02:25 0-013049.v264
-rw-r--r-- 1 nobody nogroup  69M Mar 11 03:26 0-023103.v264
-rw-r--r-- 1 nobody nogroup 5.9M Mar 11 03:31 0-033117.v264
-rw-r--r-- 1 nobody nogroup 1.5M Mar 11 03:40 0-034350.v264
-rw-r--r-- 1 nobody nogroup  17M Mar 11 04:02 0-035259.v264
-rw-r--r-- 1 nobody nogroup 306K Mar 11 04:10 0-041548.v264
-rw-r--r-- 1 nobody nogroup 4.9M Mar 11 04:23 0-042457.v264

There is a support forum, where I found the following files scattered in various posts. From what I can tell, they are the latest as of this writing. I can confirm they work with my IP391W-HD, which the system tells me is GM8126 hardware and came with firmware

  • - firmware (b56f211a569fb03a37d13b706c660dcb)
  • web.pk2 - a UI update that includes dropbox support. This is really for the model that has pan and tilt, so those buttons don't work. (0e42e42bd6f8034e87dcd443dcc3594d)
  • V264ToAVIen.exe - converts the output to an AVI file that mplayer will play (with some complaints) (9c5a858aa454fed4a0186cf244c0d234) offers free limited-time Windows VM's which will work to upload this firmware. Just make sure you use a bridged network in the VM; I'm guessing the firmware ActiveX control tells the camera to TFTP the data from it, which doesn't work via NAT.

Somewhat worryingly, you can telnet to it and get a login prompt (TASTECH login). So it has a built-in backdoor you can't disable.

There have been some efforts to hack the device. did an excellent job reverse engineering the .pk2 format and writing tenvis_pack.c (no license, I'm generously assuming public domain). I used this to recreate the firmware above with a telnet daemon listening with a shell on port 2525 (no password, just telnet to it)

It's interesting to poke around, but it seems like the whole thing is really driven by a binary called ipc8126

/ # ipc8126 --help
*** Version:
*** Release date: 2013-08-05 15:48:32

In general, I'd say hackability is quite low.

Warning : any of the above might turn your camera into a paperweight. It worked for me, but that's all I can say...

Skipping pages with django.core.paginator

Here's a little snippet for compressing the length of long Django pagination by just showing context around the currently selected page. What I wanted was the first few and last few pages always selectable with some context pages around the currently selected page; e.g.

Example of skip markers in paginator

If that's what you're looking for, some variation on below may be of use. In this approach, you build up a list of pages similar to the paginator object page_range but with only the relevant pages and the skip-markers identified.

from django.core.paginator import Paginator
import unittest

class Pages:

    def __init__(self, objects, count):
        self.pages = Paginator(objects, count)

    def pages_to_show(self, page):
        # pages_wanted stores the pages we want to see, e.g.
        #  - first and second page always
        #  - two pages before selected page
        #  - the selected page
        #  - two pages after selected page
        #  - last two pages always
        # Turning the pages into a set removes duplicates for edge
        # cases where the "context pages" (before and after the
        # selected) overlap with the "always show" pages.
        pages_wanted = set([1,2,
                            page-2, page-1,
                            page+1, page+2,
                            self.pages.num_pages-1, self.pages.num_pages])

        # The intersection with the page_range trims off the invalid
        # pages outside the total number of pages we actually have.
        # Note that includes invalid negative and >page_range "context
        # pages" which we added above.
        pages_to_show = set(self.pages.page_range).intersection(pages_wanted)
        pages_to_show = sorted(pages_to_show)

        # skip_pages will keep a list of page numbers from
        # pages_to_show that should have a skip-marker inserted
        # after them.  For flexibility this is done by looking for
        # anywhere in the list that doesn't increment by 1 over the
        # last entry.
        skip_pages = [ x[1] for x in zip(pages_to_show[:-1],
                       if (x[1] - x[0] != 1) ]

        # Each page in skip_pages should be follwed by a skip-marker
        # sentinel (e.g. -1).
        for i in skip_pages:
            pages_to_show.insert(pages_to_show.index(i), -1)

        return pages_to_show

class TestPages(unittest.TestCase):

    def runTest(self):

        objects = [x for x in range(0,1000)]
        p = Pages(objects, 10)

                         [1, 2, -1, 99, 100])



if __name__ == '__main__':

Then somehow pass through the pages_to_show to your view (below I added it to the paginator object passed) and use a template along the lines of

<ul class="pagination">

{% if pages.has_previous %}
  <li><a href="foo.html?page={{ pages.previous_page_number }}">&laquo;</a></li>
{% else %}
  <li class="disabled"><a href="#">&laquo;</a></li>
{% endif %}

{% for page in pages.pages_to_show %}
  {% if page == -1 %}
  <li class="disabled"><a href="#">&hellip;</a></li>
  {% elif page == pages.number %}
  <li class="active"><a href="#">{{ page_num }}</a></li>
  {% else %}
  <li><a href="foo.html?page={{ page_num }}">{{page_num}}</a>
  {% endif %}
{% endfor %}

{% if pages.has_next %}
  <li><a href="foo.html?page={{ pages.next_page_number }}">&raquo;</a></li>
{% else %}
  <li class="disabled"><a href="#">&raquo;</a></li>
{% endif %}


Running cloud images locally

Fedora and Ubuntu both provide compact cloud images that are useful for spinning up small VM's quickly (much quicker than installing from a huge ISO or even net-install).

Both these pages have single-click buttons to simply launch the VM's at Amazon, which is very cool. However, you may have reason to use them "offline" with a local KVM (outside of EC2 or OpenStack) for testing, or on a plane, etc. I didn't find a lot of information on this (although it is all available once you know what you're looking for).

So here's my quick guide for the complete newbie. Firstly, download your image of choice and put it in /var/lib/libvirt/images. Open up virt-manager and you can create your new VM via "import existing image".

You can try booting it, but the problem you'll hit is the images have no default password or way to log-in because, very sensibly, you're expected to inject that. Booting you'll see cloud-init attempting to contact to collect the meta-data to initalize the VM; eventually it will time out and you're left at a login prompt you can't log in at. cloud-init does many things and is very flexible with lots of different plugins to initialise images in various ways. The particular one we're interested in is the No cloud plugin. This will look for data from a locally attached CD drive, which works very easily for this scenario.

Now that you know that's what you're looking for, the instructions are fairly clear; I'll repeat them just for clarity. Firstly you want to create a minimal meta-data file that has a host-name and an instance-id:

$ cat meta-data
instance-id: iid-local01
local-hostname: myhost

Modifying the instance-id will signal to cloud-init that it should run again because something changed. This is also where you can put static IP address data; see the documentation.

Secondly, create a user-data file that has the commands to enable password login; set a password, and inject your ssh public key so you can easily log-in:

$ cat user-data
password: mypassword
ssh_pwauth: True
chpasswd: { expire: False }

  - ssh-rsa ... (insert ~/.ssh/ here)

Note for new players: that #cloud-config isn't an optional comment, it's a directive. If you leave it out, you'll probably see a little something about Unhandled non-multipart userdata starting... and your changes won't apply.

Insert those two into files into an iso:

$ genisoimage -output init.iso -volid cidata -joliet -rock user-data meta-data

Then copy init.iso into /var/lib/libvirtd/images as well, and connect that as a virtual-cd drive to your virtual-machine created from the image.

When you boot you should see some output as it injects your key. It should get an address via DHCP and then you should be able to log-in with fedora or ubuntu users. Then you can start getting more complicated with things like static addresses, package installations, running commands, etc by reading the documentation.

Skipping bash history for command-lines starting with space

I was recently reading about a case where part of the evidence appears to be a deleted bash history-file. From what I gather, the accused says that the removal was a clean-up job to remove inadvertently stored passwords rather than an attempt to hide nefarious activity.

What had managed to pass me by in 15 or so years of using bash but not reading man bash properly is the HISTCONTROL variable. If it is set to ignorespace then commands entered with a leading-space will not be stored in the history. Like all the best discoveries I found this only by accident on a machine where it was turned on.

It's been quite useful in keeping my history pruned. However, not usually for security reasons around hiding passwords — passwords on the command-line have other problems and I'm sure any security person would tell you not to use them just from a defense-in-depth perspective. That said, from a "keeping ctrl-r reversi-search useful" point-of-view it's often helpful; for example I've mostly trained my fingers to <space>rm -rf because I'm sure I'm not the only one who has deleted the wrong thing via a history-recall-combined-with-typing-to-fast scenario.

So, HISTCONTROL=ignoreboth (which also ignores duplicates) is certainly a useful one to slip into your .bashrc. At least it would be one-less thing to explain to the FBI!

Converting an American propane appliance to Australian gas bottles

Here's something I just spent too much time figuring out...

If you have an Australian "gas" or "LPG bottle"; the type you'd pick-up at any "service" or "petrol" station in Australia, it has a female POL connector. I'm not sure what POL stands for; possibly related to some company who made connectors long ago and it became standard.

If you have an American "propane" device such as a grill, turkey fryer or smoker, or indeed something that plugs into a "propane bottle" you would pick-up at a "gas station" -- it will have a "Type 1", "ACME", "ACME Type 1", "QCC", "QCC1" or "QCC Type 1" connector (each seems to be an interchangeable term for the other). The appliance side of this has a big (usually black) plastic nut that is apparently safer or something.

Once you have figured this out, you can buy something like the "Grillpro Model 11051 Universal Fit Propane Tank Adapter" and I can attest, based upon empirical evidence, that things will "just work". Of course your other choice might be just to replace the regulator, hoses, etc.; however if everything seems super-glued together the adapter is much easier.

In other empirical evidence you won't find anywhere else on the internet : the Vizio M3D550KD LCD television works just fine on 240V, despite not being rated for it on the back.

Stuck keyboard with Fedora 17 under VirtualBox

For a while now I've been plagued with this ridiculous problem of the keyboard becoming "stuck" in my Fedora 17 VM running under VirtualBox. Keys would stop working until you held them down for several seconds, making typing close to impossible.

Of course my first thought was to blame VirtualBox, since it has a lot to do with the keyboard. I found out some interesting things, like you can send scan-codes directly to virtual-machines with something like

$ VBoxManage controlvm UUID keyboardputscancode aa

(get the UUID via VBoxManage list vms; figuring out scan-codes is left to the reader!).

I noticed the problem primarily happening while emacs was in the foreground, meaning I was working on code or an email ... my theory was when I typed too fast some race got hit and put the keyboard into a weird state that a reboot fixed.

Well it turns out the problem is almost the exact opposite and nothing to do with VirtualBox, scan-codes or race-conditions. Luckily, today I noticed "slow keys enabled" warning that sprung-up and went away quickly just before the keyboard stopped. Once I saw that the game was up; turns out this is a well-known bug that is easily fixed with xkbset -sl. It happens because I was typing too slowly; holding down the shift-key while I thought about something probably.

Hopefully this saves someone else a few hours!

Debugging puppetmaster with Foreman

This is a little note for anyone trying to get some debugging out of the puppetmaster when deploying with Foreman.

The trick, much as it is, is that Foreman is running puppet via Apache; so if you're trying to start a puppet master daemon outside that it won't be able to bind to port 8140. You thus want to edit the config file Apache is using to launch puppet /etc/puppet/rack/ It's probably pretty obvious what's happening when you look in there; simply add

ARGV << "--debug"

and you will start to get debugging output. One issue is that this goes to syslog (/var/log/messages) by default and is a lot of output; so much so that it might get throttled. Although you can certainly reconfigure your syslog daemon to split out puppet logs, an easier way is to just skip syslog while you're debugging. Don't be fooled by config options; simply add

ARGV << "--logdest" << "/var/log/puppet/puppet-master.debug"

to the same file to get the logs going to a separate file. Don't forget to restart Apache so the changes stick.