CHAPTER 2 ■ APPLIANCE HACKING 78 This might be to record the sound with vox_record.sh: #!/bin/bash LOGFILE=/var/log/voxrecordpid DIR_INCOMING=/usr/local/media/voxrecord if [ "$1" == "start" ]; then FILENAME=`mktemp -p $DIR_INCOMING`.wav arecord -f cd -t wav $FILENAME >/dev/null >/dev/null 2>&1 & PID=$! echo $PID >$LOGFILE fi if [ "$1" == "stop" ]; then PID=`cat $LOGFILE` kill $PID rm $LOGFILE fi or play back each sound in the directory with vox_play.sh: #!/bin/bash DIR_INCOMING=/usr/local/media/voxrecord for F in "$DIR_INCOMING"/*.wav do play $F done or even delete them all through vox_delete.sh: #!/bin/bash DIR_INCOMING=/usr/local/media/voxrecord rm -f $DIR_INCOMING/* Naturally, there is a lot more scope here to support the deletion of individual recordings, and so on. But this represents the idea. ■ Note The Minerva system abstracts these ideas out into Minx, which eliminates the need for separate executables for each Arduino application. Minerva will be covered in Chapter 7. CHAPTER 2 ■ APPLIANCE HACKING 79 Joysticks for Input Joysticks, particularly old ones, make wonderful input devices because they interface with the parallel port on most standard sound cards and are physical rugged. This enables the buttons to be reused, particularly as foot pedals, to control software. Indeed, this provides a very cheap way of adding a dictation module to your machine, without the need for an Arduino providing the input. In addition to triggering individual events on a Linux machine, such as requesting a weather report or the state of the machine, it can also feed messages to other applications. mplayer, for example, can operate in slave mode, allowing commands to be fed to it from the standard input or a named pipe. Similarly, the X Window TV-viewing software, xawtv, comes with xawtv-remote to change channel and volume (as per most remote controls), giving you capture on/off and screenshot facilities. This makes it possible to freeze frame magic shows to see how they do it! You can read the joystick directly from /dev/js0, but it is usually better to use an abstraction, like the Simple DirectMedia Layer (SDL). This allows you to port the code elsewhere if necessary, avoid the vagaries that come with a reliance on the device hierarchy, and make it easier for others to add and adapt your code. The code to read and process the joystick is a very simple loop of C code: #include <SDL/SDL.h> int main() { if (SDL_Init(SDL_INIT_JOYSTICK) < 0) { fprintf(stderr, "Couldn't initialize SDL: %s\n", SDL_GetError()); exit(1); } SDL_JoystickEventState(SDL_ENABLE); SDL_Joystick *pJoystick = SDL_JoystickOpen(0); SDL_Event event; while(SDL_PollEvent(&event)) { switch(event.type) { case SDL_JOYBUTTONDOWN: // Use event.jbutton.which, event.jbutton.button, event.jbutton.state break; } } SDL_JoystickClose(pJoystick); return 0; } The button presses can naturally trigger software internally or make use of the Minerva Minx system I mentioned earlier to execute separate external scripts (Minerva is covered fully in Chapter 7). Some joysticks can also be used as output devices, through an technique known as force feedback, available under Linux with libff. This functionality is provided through one of two drivers, HID driver (hid-lg2ff) or I-Force driver (iforce.ko), which cover a number of the force feedback devices on the market. Alas, not all of them are included, so it is best to check compatibility first (http://sourceforge. net/apps/mediawiki/libff/index.php?title=SupportedDevices). The use of force feedback is primarily for games, because the game causes a slight jolt of the device, through a small motor in the joystick, CHAPTER 2 ■ APPLIANCE HACKING 80 when the player is attacked or dies. The vibrate option on mobile phones and pagers works in the same way. There is very little scope for shaping the vibration in any advanced or meaningful way, and very few (if any) games in Linux support the library. However, fftest (from the ffutils project at http://sourceforge.net/projects/libff/files/ffutils) may be hacked to provide a small rumble when an e-mail arrives. Other Input Controllers Game development has never been a strong selling point to the Linux community; consequently, the libraries available (and the resultant quality of the games) have been few in number. This has led to a sporadic approach to the problem of device control. One good example of this is the separation between SDL (for good solid joystick processing, but with force feedback currently available only in an unstable SVN branch) and fflib (for force feedback). There is currently just one project that is attempting to close this divide, and it’s called the Object Oriented Input System (OIS); you can find it at http://sourceforge.net/projects/wgois/. OIS is planning on abstracting away all the device (and driver) specific elements of user input devices (including keyboard, mice, and joysticks) and providing a unified API to them. Although this is admirable for the games developers, it doesn’t help us a great deal except for the recent introduction of code that supports the Nintendo Wii’s remote wand (aka the Wiimote). This peripheral operates through Bluetooth and can determine the area of the screen it’s pointing at by imaging into its sensor the infrared LEDs held in a bar attached to the top or bottom of the screen. This can also determine its orientation and acceleration. This makes it a very suitable controller for complex applications running on a TV screen, where a mouse is not suitable but an equivalent means of control is needed. There is also the CWiid tool set (part of the www.wiili.com project), which provides a mouse driver wrapper, allowing unported mouse-based applications to be controlled by the Wiimote. Hacking Laptops The price of netbooks, with solid-state storage and preinstalled Linux software, are now so low that their cost isn’t much greater than the top-of-the-range stand-alone photo frames. And as a bonus, you get a better processor, video playback, network connectivity (often wireless), and VoIP software. This makes the netbook an ideal home automation panel, with many uses. Obviously, older laptops can also be used for hacking. Any that are lacking a hard drive, have dead batteries, or have broken keyboards are particularly good value since the cost of new parts makes them too expense to rebuild, and having a laptop reliant on a tethered power line is not such a problem for home automation users as it is for others. Their use as a control panel is obvious, because the screen and keyboard halves can be folded flat and mounted to any wall or surface quite easily. Or, the keyboard base (with the lion’s share of electronics) can be hidden away underneath a desk or worktable, with just the screen poking out. It can then be controlled with a joystick input or, more impressively, a touchscreen. Touchscreens can be added retroactively to most laptops. They exist as a transparent membrane that fits over the screen and a PS/2 socket that mimics the behavior of a mouse delivering X and Y coordinates and left-button up and down messages. It should be noted that the software interface must be suitably programmed, since the membrane cannot detect the mouse position unless there is pressure on it, and there is no input for a right mouse button. Fortunately, most web interfaces are generally suitable. CHAPTER 2 ■ APPLIANCE HACKING 81 ■ Note The touchscreen membranes cannot be cut to the size of your laptop; they must be bought presized, so check carefully before purchasing, and remember that screen size is measured diagonally across the LCD screen itself, not the visible area. Your Own X10 Devices Even some hardened geeks balk at the idea of creating hacks with mains electricity. 11 But with a little care and attention, you can add X10 control to any mains-powered device, such as water heaters, heaters, garage door motors, and so on. You can even wire them directly to standard consumer equipment (like modems and printers) to reboot or power cycle them. Building an entire X10 unit to control a motor, for example, is so far beyond the scope of this book that it wouldn’t be fair to try. Instead, I will show an inline appliance module, such as the AM12W, which handles the dirty work of processing the protocol and results in a set of closed contacts between two of its connections. It works in the same way as the AM12 you saw in Chapter 1 (although slightly cheaper), but instead of controlling the flow of current to a plug socket, it controls the flow between the mains and the X10 unit and between the unit and the device. Figure 2-8 shows this wiring. Figure 2-8. Connecting an AM12W to a mains-powered device 11 Since January 1, 2005, in England and Wales, the Building Regulations Part P specifies that only certified engineers can carry out this particular electrical installation work. If it not carried out by such a person, then the work must be certified upon completion. Other countries may have similar laws. CHAPTER 2 ■ APPLIANCE HACKING 82 This works for any unit that is remotely controlled only through X10. To support a local switch (either in the on/off variety or a momentary push button), a better choice of module is the AD10. This also supports a manual override on the device, shown as the blue button in Figure 2-9. Figure 2-9. The AD10 module Figure 2-10 shows the wiring; although both types of button are featured here, only one would be used in practice. Figure 2-10. Wiring an AD10 to a mains-powered device The main advantage of this module over the AM12W is that the switches used are standard electrical ones and not the (more expensive) X10 variety. . technique known as force feedback, available under Linux with libff. This functionality is provided through one of two drivers, HID driver (hid-lg2ff) or I-Force driver (iforce.ko), which cover a number. wrapper, allowing unported mouse-based applications to be controlled by the Wiimote. Hacking Laptops The price of netbooks, with solid-state storage and preinstalled Linux software, are now so low. preinstalled Linux software, are now so low that their cost isn’t much greater than the top-of-the-range stand-alone photo frames. And as a bonus, you get a better processor, video playback, network