Have you ever wondered if you're meeting the same people every day on your daily commute? Over half a million people ride the Warsaw Metro daily, but if I arrive at the station at roughly the same time every day, surely there must be others with similar schedules? But even after almost a year of taking the same route, I couldn't recognize any familiar faces. So I decided it was time for a more scientific approach.
A surprisingly large number of people leave their phone's Bluetooth in discoverable state (I find it strange, because on most phones I've seen the default behavior is only to become discoverable for 120 seconds or so when pairing). I thought if I scanned for Bluetooth devices every time I rode the subway and saved the results, I could then check if I ever saw the same device on different days. So that's what I did, I made an application for my phone that does a Bluetooth scan and logs all devices it sees in a SQLite database. That was not ideal yet, because I still had to trigger the scan manually every time (I didn't want to keep scanning all the time, because that would quickly drain the battery and also I'd get a lot of false positives from my neighbors, coworkers etc.). Happily, there is a solution. Living in a city, just about the only time I lose cell phone signal is when I get on the subway. So that's a good condition to wait for to trigger the scan (there will be occasional false positives, but they don't bother us much). Obviously, this only works if your commute involves riding the subway and not, say, a bus.
Here's the source code of the application if you'd like to play with it.
So are there any strangers that happen to commute at the same time I do? After just two weeks of the experiment, with the help of a SQL query:
select addr, count(*), max(sightingtime)-min(sightingtime) y, group_concat(sightingtime) from sighting group by addr having y > 3600 order by y desc;
I found two persons that I shared a subway ride with on two different days. Unfortunately I can't really say much about them, except for the fact that one of them had an LG phone and the other a Samsung.
2012-08-21
2012-02-21
Electricity meter fun
At the place I live, the electricity meter looks like this:
The fancy display shows total kilowatt hours and maximum power consumption, but it doesn't show current consumption. Instead it has this blinking red light - the faster it blinks, the higher the power consumption. But to get the actual figure, I'd have to count how many times it blinked, measure the time and then do some arithmetic. And that would be pedestrian. Instead I wrote an application for my phone that does the measurements (with the phone's camera) and displays the current power consumption:
Here's the source code if anyone's interested.
The fancy display shows total kilowatt hours and maximum power consumption, but it doesn't show current consumption. Instead it has this blinking red light - the faster it blinks, the higher the power consumption. But to get the actual figure, I'd have to count how many times it blinked, measure the time and then do some arithmetic. And that would be pedestrian. Instead I wrote an application for my phone that does the measurements (with the phone's camera) and displays the current power consumption:
Here's the source code if anyone's interested.
2011-12-31
NXT Drawbot
When I saw this drawbot, I immediately thought it was something I should be able to recreate with Lego Mindstorms. And so I did. The idea is simple, there's a pen suspended on thread from motors in the corners. When the motors wind or unwind the thread, the pen moves and draws a line. The rest is a simple application of the Pythagorean theorem to move the pen where we want it.
When watching other drawbots on YouTube etc. I was surprised to see they were able to achieve a level of precision that allows them to recreate pictures by effectively drawing each of their pixels with clever patterns. My bot clearly lacks such precision. I think the main reason for that is the friction between the pen and the drawing surface. Each time the pen is about to start moving, there's a noticeable moment before it breaks away from the static friction. That makes the bot incapable of very small precise movement. There's another source of imprecision - since the radius of the spools that the threads are wound onto is small, the difference in radius when there is no thread wound and when there is a lot of thread wound on the spool is non-negligible.
Here are some more pictures of the bot.
When watching other drawbots on YouTube etc. I was surprised to see they were able to achieve a level of precision that allows them to recreate pictures by effectively drawing each of their pixels with clever patterns. My bot clearly lacks such precision. I think the main reason for that is the friction between the pen and the drawing surface. Each time the pen is about to start moving, there's a noticeable moment before it breaks away from the static friction. That makes the bot incapable of very small precise movement. There's another source of imprecision - since the radius of the spools that the threads are wound onto is small, the difference in radius when there is no thread wound and when there is a lot of thread wound on the spool is non-negligible.
Here are some more pictures of the bot.
2011-10-20
Google Earth with a PS3 controller
Google Earth is a lot of fun with a 3D input device. But not everyone can justify shelling out a hundred bucks or so on a SpaceNavigator just to play with Google Earth. I've explored other possibilities, but the best alternative I've come up with is the PS3 controller. It has more than enough joysticks and buttons for five degrees of freedom. Have a look:
The PS3 controller is pretty well supported under Linux (at least if you connect it with a USB cable, it's more complicated if you want to use Bluetooth). The only problem really is mapping its various buttons and joysticks to proper functions in Google Earth. Fortunately, there is a piece of software called pystromo that can freely remap input events, thus allowing us to turn a PS3 controller into a SpaceNavigator-lookalike.
Here's what you need to do.
- Download and unpack pystromo.
- Open the lib/constants.py file in the pystromo directory with a text editor. Find the line containing "ABS_MISC" and add the following two lines after that (before the curly brace):
48: "ABS_L2", 49: "ABS_R2",
(We have to do this, because pystromo doesn't have constants for the PS3 controller's L2 and R2 buttons.) - Create a new file in the pystromo directory and call it, say, config/ps3-ge.map. Put the following in it:
[Device:dualshock] vendor=0x054c product=0x0268 [Map:dualshock] ABS_X@0~255:ABS_X@0~255 ABS_Y@0~255:ABS_Y@0~255 ABS_Z@0~255:ABS_RZ@0~255 ABS_RZ@0~255:ABS_RX@255~0 ABS_L2@0~255,ABS_R2<1:ABS_Z@127~0 ABS_R2@0~255,ABS_L2<1:ABS_Z@127~255
- Connect your PS3 controller using a USB cable and press the PS button.
- As root, run the following command: ./pystromo-remap.py -R -v -m config/ps3-ge.map
- This will create a new input device, called eventN in /dev/input/. The one you're looking for is the one with the highest number. As root, run this to give your regular user access to the device: chmod 666 /dev/input/eventN
- Open /opt/google/earth/free/drivers.ini with a text editor and put the following after the "SETTINGS" line (after the curly brace), remembering to replace eventN with the proper device number:
SpaceNavigator/sensitivityX = 0.4 SpaceNavigator/sensitivityY = 0.4 SpaceNavigator/sensitivityZ = 0.1 SpaceNavigator/sensitivityPitch = 0.05 SpaceNavigator/sensitivityYaw = 0.05 SpaceNavigator/sensitivityRoll = 100 SpaceNavigator/device = /dev/input/eventN SpaceNavigator/zeroX = 127 SpaceNavigator/zeroY = 127 SpaceNavigator/zeroZ = 127 SpaceNavigator/zeroPitch = 127 SpaceNavigator/zeroYaw = 127 SpaceNavigator/zeroRoll = 127
- Run Google Earth.
You should now be able to navigate using the left and right sticks and L2/R2 buttons.
2011-10-17
Control Google Earth with an Android tablet
I have previously described how to turn an Android device into a mouse under Linux, using the uinput module. There's no reason we should limit ourselves to a simple mouse. Some applications benefit from a multi-axis controller, which we can simulate in a similar way. One such application is Google Earth. Here's a demonstration video:
And here's how it's done. Just as before, there's an application running on the tablet that listens for touch events and broadcasts them on the network and a Python script running on the computer that listens for those events and translates them to simulated controller events that Google Earth understands. Here's the tablet application's source code and here's just the APK if you don't want to compile it yourself. The Python script that's running on the computer is here.
There are some additional hoops you have to jump through to get it running.
- The Python part requires python-uinput, which in turn requires libsuinput.
- Remember to unblock UDP port 20125 on your computer's firewall, as that's the port that the tablet application uses to broadcast touchscreen events (the tablet and the computer obviously have to be on the same network).
- Run android3dmouse.py as root.
- Run the TouchscreenBroadcaster3D application on your Android device and touch the screen (the simulated mouse device only appears on the computer after the first events are emitted).
- Look in /dev/input/ and figure out what the newly created device is called (it's going to be the eventN file with the highest number).
- As root, execute the following command to let Google Earth running as a regular user access the device: chmod 666 /dev/input/eventN
- Open /opt/google/earth/free/drivers.ini with a text editor and paste in the following after the "SETTINGS" line (after the curly brace), remembering to replace eventN with the proper device name:
SpaceNavigator/sensitivityX = 80 SpaceNavigator/sensitivityY = 80 SpaceNavigator/sensitivityZ = 30 SpaceNavigator/sensitivityPitch = 0.5 SpaceNavigator/sensitivityYaw = 0.5 SpaceNavigator/sensitivityRoll = 0.5 SpaceNavigator/device = /dev/input/eventN SpaceNavigator/zeroX = 0.0 SpaceNavigator/zeroY = 0.0 SpaceNavigator/zeroZ = 0.0 SpaceNavigator/zeroPitch = 0.0 SpaceNavigator/zeroYaw = 0.0 SpaceNavigator/zeroRoll = 0.0 SpaceNavigator/gutterValue = 0
- Since X happily grabbed the new device and it now moves the mouse cursor, execute the following command to make X let it go: xinput set-int-prop "python-uinput-mouse" "Device Enabled" 8 0
- Finally, run Google Earth.
You should now be able to pan, zoom and rotate via multi-touch gestures on your tablet's (or phone's) screen. (Yes, one more degree of freedom would be nice, but I haven't figured out a good way to do it yet.)
If you can't get this mess to work, I'm not the first one to do something like this, there's a Google Summer of Code project done by Reese Butler that works in a similar manner, but uses a slightly different control scheme. The Android part is on the Market and the computer part can be found here. Maybe you'll have more luck with that one.
2011-08-19
Android phone as a touchpad for a PC
The Linux kernel has a module named uinput that allows userspace programs to simulate input devices like mice, keyboards and joysticks. I used this neat mechanism to turn my Android phone into a touchpad for my computer.
Here's how it works. On the phone there's an application that broadcasts touchscreen events over the network. You can get the application's source here. On the PC there's a script running that listens for the events and translates them into mouse events that get injected into the system via uinput, at which point the X server sees them and moves the mouse pointer accordingly. That part is written in Python and requires the python-uinput module (which in turn requires libsuinput). You can get its source here.
As always, there's room for improvement. I used my phone's trackball as left mouse button, but for phones or tablets that have no trackball it would probably make sense to use some regions of the screen as buttons. It would also be interesting to add multitouch gestures for scrolling and zooming. Another thing that comes to mind is to use the phone as a 3D controller for Google Earth. Four degrees of freedom should be doable with the touchscreen alone via two-finger gestures and maybe we could use the phone's other sensors like the accelerometer and gyroscope (which my Nexus One lacks, but newer phones have them) to get all six.
Here's how it works. On the phone there's an application that broadcasts touchscreen events over the network. You can get the application's source here. On the PC there's a script running that listens for the events and translates them into mouse events that get injected into the system via uinput, at which point the X server sees them and moves the mouse pointer accordingly. That part is written in Python and requires the python-uinput module (which in turn requires libsuinput). You can get its source here.
As always, there's room for improvement. I used my phone's trackball as left mouse button, but for phones or tablets that have no trackball it would probably make sense to use some regions of the screen as buttons. It would also be interesting to add multitouch gestures for scrolling and zooming. Another thing that comes to mind is to use the phone as a 3D controller for Google Earth. Four degrees of freedom should be doable with the touchscreen alone via two-finger gestures and maybe we could use the phone's other sensors like the accelerometer and gyroscope (which my Nexus One lacks, but newer phones have them) to get all six.
2011-07-03
On keyboards
Many people don't care about keyboards. I do. But unlike most keyboard enthusiasts, who focus on the switches (mechanical vs. rubber dome etc.) and are prepared to give long lectures on buckling springs and how the IBM Model M is the greatest keyboard of all time (which is probably true), I don't care that much about switches. I can't stand keyboards with wrong key layouts. I don't mean Dvorak vs. QWERTY, I mean the physical layout of the keys. And by "wrong" I mean pretty much any layout that's different from the standard full-size one. (That's one of the reasons I don't see myself using a laptop for anything serious anytime soon.)
Fortunately, most full-size keyboards have sane key layouts. There are two issues with modern keyboards that drive me crazy. One is the "menu" key introduced by Microsoft some time around Windows 95. Notice that I don't even mind the Windows logo keys that much. An additional modifier key is sometimes useful. Mac keyboards have three modifier keys on the bottom row, classic Unix keyboards often had them as well. I don't even care that it's the Windows logo, not some OS-agnostic symbol. But the "menu" key? What is it for? I don't think I've ever seen it used for anything. It's useless and it messes up the symmetry of the layout (three modifier keys on each side of the space bar). It also means the space bar is too short. So that's the first of my keyboard-related pet peeves. As you're about to see, I care about the second one much more deeply.
Numeric keypads. I hate them. I guess they're useful if you're an accountant and must input a lot of numbers into your spreadsheets. I'm not an accountant. I imagine to most people the numeric keypad is as useless as it is to me. The last time I remember using it is when we were playing Mortal Kombat fifteen years ago. So what, I hear you say. Just don't use it. But you see, it takes up space that I need for something else, namely the mouse. I need my keyboard positioned so that the monitor's symmetry axis goes between the G and H keys. That way my arms are positioned in a natural symmetric way when typing. That means that if my keyboard has a numeric keypad, the mouse goes too far to the right. I'm pretty sure it's not just annoying, but also not good for my posture.
What can we do about this sad state of affairs? Aren't there any good keyboards? Well, there are. Bad news is, they're not exactly cheap. I have two candidates for "the perfect keyboard". One is the space saving variant of the previously mentioned Model M:
In a lot of ways, it is the Holy Grail. An elegant weapon for a more civilized age. No numeric keypad, no stupid Windows keys. Built like a tank. Likely to outlive its user. There are downsides though. And I'm not even talking about the loud click, which is sure to drive your coworkers and roommates crazy. Problem is, the keyboard is long out of production and it is the less popular variant of the Model M. So when one of them shows up on eBay, it easily goes for more than 200 USD.
Is there no keyboard with all the right features that is still in production? As it happens, there is, the Realforce 86U:
As you can see, it has the Windows logo keys, but as I said, they don't bother me. What's important is that there's no "menu" key next to the right Control. And no numeric keypad of course. What's the catch? The keyboard might be in production, but it doesn't mean it's cheap. It currently goes for 265 USD on EliteKeyboards. Ouch.
I'm not aware of any cheaper keyboards that would match all my criteria (no menu key, no numeric keypad, standard full-size layout otherwise). If you're not ready to shell out two hundred bucks or more on a keyboard, you have to start making compromises. The one I'm probably willing to make is to accept the menu key. I still think it's extremely idiotic, but I guess I can live with it. If we allow the menu key, that opens up several possibilities in the 100-150 USD range. EliteKeyboards currently carries some nice keyboards from Leopold and Amazon has several Filco Majestouch keyboards to choose from. Both brands seem reasonable, but they're still a bit pricey. Like I said, most keyboard geeks obsess about the mechanical switches ("Cherry" switches in the case of Leopolds and Filcos) and they don't come cheap.
An important thing to know when looking for keyboards with no numeric keypad is that they're called "tenkeyless". Don't waste your time looking for "space saver" keyboards as they're almost always some ugly layouts that keep the numeric keypad, but drop the arrow keys/page up/page down area (a notable exception is the Model M mentioned above). I really don't understand the thinking behind such layouts. What I understand even less are the laptop keyboards with numeric keypads. And they are getting popular. I guess on 15-inch and bigger laptops there is enough space for extra keys, but why would you waste it on a numeric keypad and not, say, reasonable sized arrow keys and page up/page down etc. Another problem with such laptops is the already mentioned asymmetry. It's impossible to position your arms comfortably when typing, when the home row of the keyboard is shifted to the left (and obviously you can't reposition the laptop's keyboard in relation to the screen).
One day Logitech will make a nice, cheap, "tenkeyless" keyboard. But it probably won't be tomorrow, so what can you do in the mean time? Well, you can take inspiration from this guy, who shares my dislike for numeric keypads, take a keyboard that has a numeric keypad and... chop it off. It's what I did to a Logitech UltraX:
It turned out to be more difficult than I thought (the keyboard looks cheap, but there's a metal plate inside that I had to saw off) and it may not look pretty, but in the end I have a keyboard with a reasonable layout that didn't cost an arm and a leg. If you want to try it yourself, some instructions can be found on wikiHow. Obviously the details will depend on the exact keyboard model that you choose to lobotomize.
If you're considering becoming a keyboard otaku, I strongly recommend that you check out geekhack.org, they have an active forum and a wiki with more information on keyboard switches than a sane person needs.
Update (September 2012): As of right now, the CM Storm Quick Fire Rapid seems to be the most reasonably priced tenkeyless keyboard. The Cherry MX blue version goes for 64 USD on Amazon.
Update (August 2013): I just found this HP keyboard, not very pretty, but with mostly correct layout and only 26 USD on Amazon.
Fortunately, most full-size keyboards have sane key layouts. There are two issues with modern keyboards that drive me crazy. One is the "menu" key introduced by Microsoft some time around Windows 95. Notice that I don't even mind the Windows logo keys that much. An additional modifier key is sometimes useful. Mac keyboards have three modifier keys on the bottom row, classic Unix keyboards often had them as well. I don't even care that it's the Windows logo, not some OS-agnostic symbol. But the "menu" key? What is it for? I don't think I've ever seen it used for anything. It's useless and it messes up the symmetry of the layout (three modifier keys on each side of the space bar). It also means the space bar is too short. So that's the first of my keyboard-related pet peeves. As you're about to see, I care about the second one much more deeply.
Numeric keypads. I hate them. I guess they're useful if you're an accountant and must input a lot of numbers into your spreadsheets. I'm not an accountant. I imagine to most people the numeric keypad is as useless as it is to me. The last time I remember using it is when we were playing Mortal Kombat fifteen years ago. So what, I hear you say. Just don't use it. But you see, it takes up space that I need for something else, namely the mouse. I need my keyboard positioned so that the monitor's symmetry axis goes between the G and H keys. That way my arms are positioned in a natural symmetric way when typing. That means that if my keyboard has a numeric keypad, the mouse goes too far to the right. I'm pretty sure it's not just annoying, but also not good for my posture.
What can we do about this sad state of affairs? Aren't there any good keyboards? Well, there are. Bad news is, they're not exactly cheap. I have two candidates for "the perfect keyboard". One is the space saving variant of the previously mentioned Model M:
In a lot of ways, it is the Holy Grail. An elegant weapon for a more civilized age. No numeric keypad, no stupid Windows keys. Built like a tank. Likely to outlive its user. There are downsides though. And I'm not even talking about the loud click, which is sure to drive your coworkers and roommates crazy. Problem is, the keyboard is long out of production and it is the less popular variant of the Model M. So when one of them shows up on eBay, it easily goes for more than 200 USD.
Is there no keyboard with all the right features that is still in production? As it happens, there is, the Realforce 86U:
As you can see, it has the Windows logo keys, but as I said, they don't bother me. What's important is that there's no "menu" key next to the right Control. And no numeric keypad of course. What's the catch? The keyboard might be in production, but it doesn't mean it's cheap. It currently goes for 265 USD on EliteKeyboards. Ouch.
I'm not aware of any cheaper keyboards that would match all my criteria (no menu key, no numeric keypad, standard full-size layout otherwise). If you're not ready to shell out two hundred bucks or more on a keyboard, you have to start making compromises. The one I'm probably willing to make is to accept the menu key. I still think it's extremely idiotic, but I guess I can live with it. If we allow the menu key, that opens up several possibilities in the 100-150 USD range. EliteKeyboards currently carries some nice keyboards from Leopold and Amazon has several Filco Majestouch keyboards to choose from. Both brands seem reasonable, but they're still a bit pricey. Like I said, most keyboard geeks obsess about the mechanical switches ("Cherry" switches in the case of Leopolds and Filcos) and they don't come cheap.
An important thing to know when looking for keyboards with no numeric keypad is that they're called "tenkeyless". Don't waste your time looking for "space saver" keyboards as they're almost always some ugly layouts that keep the numeric keypad, but drop the arrow keys/page up/page down area (a notable exception is the Model M mentioned above). I really don't understand the thinking behind such layouts. What I understand even less are the laptop keyboards with numeric keypads. And they are getting popular. I guess on 15-inch and bigger laptops there is enough space for extra keys, but why would you waste it on a numeric keypad and not, say, reasonable sized arrow keys and page up/page down etc. Another problem with such laptops is the already mentioned asymmetry. It's impossible to position your arms comfortably when typing, when the home row of the keyboard is shifted to the left (and obviously you can't reposition the laptop's keyboard in relation to the screen).
One day Logitech will make a nice, cheap, "tenkeyless" keyboard. But it probably won't be tomorrow, so what can you do in the mean time? Well, you can take inspiration from this guy, who shares my dislike for numeric keypads, take a keyboard that has a numeric keypad and... chop it off. It's what I did to a Logitech UltraX:
It turned out to be more difficult than I thought (the keyboard looks cheap, but there's a metal plate inside that I had to saw off) and it may not look pretty, but in the end I have a keyboard with a reasonable layout that didn't cost an arm and a leg. If you want to try it yourself, some instructions can be found on wikiHow. Obviously the details will depend on the exact keyboard model that you choose to lobotomize.
If you're considering becoming a keyboard otaku, I strongly recommend that you check out geekhack.org, they have an active forum and a wiki with more information on keyboard switches than a sane person needs.
Update (September 2012): As of right now, the CM Storm Quick Fire Rapid seems to be the most reasonably priced tenkeyless keyboard. The Cherry MX blue version goes for 64 USD on Amazon.
Update (August 2013): I just found this HP keyboard, not very pretty, but with mostly correct layout and only 26 USD on Amazon.
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