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Archive: Electronics

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February 16, 2008

Vector MAME

There's a special place reserved in my digital heart for the classic arcades like Tempest and Asteroids, and ironically it's because of the flawless analog goodness of their vector-based displays. I still boot up a Tempest emulator for the Dreamcast from time to time, though while it remains fun to play, it just has no soul on a standard CRT.

There was a post on MAKE a couple months ago about a guy named James Brown who hacked a driver for MAME that displays on an oscilloscope via a soundcard's analog output. Unfortunately, aside from photos, videos and a Gizmodo interview, I don't believe drivers or a howto ever turned up for this.

I spoke with the Google about this subject today, and I came across the VectorMAME and the Zector Vector Generator (ZVG):

There were more than 30 vector based games made in the 80's. To acquire a collection that includes all these games would be a monumental feat. Just to find that many vector monitors alone would be no easy task, not to mention the cost! Vector based arcade monitors haven't been made in 20+ years, and you can't simply use one vector monitor for all these games. Each monitor has different specs and runs at different speeds, making them incompatible between different gaming hardware. The hardware was unique for most of these games, making Multigame conversion kits difficult to design. And good luck finding an Aztarac, Sundance, 4-Player Eliminator, or one of our namesake, a Zektor cabinet! Some games are rare enough that even lots of money can't get you one!
After collecting vector games for years, the realization that you can never have them all sank in, and we looked for an alternative. Why not build a Vector Generator that would somehow attach to a standard PC and run all the games supported by an emulator, such as MAME, on a single vector monitor? It would be kind of a 30+ Vector Multigame!

The ZVG connects to your PC via parallel port, and Zector claims it is able to drive most old analog vector monitors that you are able to obtain. It's even able to drive an oscilloscope in X/Y mode. VectorMAME provides the ZVG drivers for DosMAME, which would allow you to put together a MAME cabinet that will play all of the old vector games on a real X/Y monitor. The hardware will set you back a couple hundred bucks, but it appears that this might be the only way to play some of your old favorites in all their glory.

Does anyone know if soundcard-oscilloscope drivers ever became available? It's not as fun as a full 19-inch monitor, but I'm surprised that this hack hasn't been released or recreated at this point.

Zector Vector Generator and VectorMAME - Link
MAME on an Oscilloscope: James Brown Interview - Link

February 15, 2008

Hack request: electronic cat door

An anonymous reader requested a hack today to solve a particular kind of kitty problem. Specifically, the reader wants to know if there's a way to have a cat door that grants access to particular cats while restricting entry or exit for others. Not being a cat owner, I don't follow cat electronics too closely, but I have heard of a project or two that are similar in nature, and I'd like to open this up for further discussion in the comments.

The photo above is from the Flo Control project. This cat, Flo, had a nasty habit of bringing in dead mice to the house. Her owner created a computer controlled system that captures an image of the cat as it approaches the door. The PC does some image recognition to determine if the cat's silhouette is atypical (ie. carrying something nasty) and only unlocks the door if the cat is sans-mouse.

One element that's used in the Flo Control setup is a cat door product made by Cat Mate. They make a few different models of cat doors that require your cat to wear a special collar to be allowed through. These are typically operated by a magnet or infra-red beacon in the collar which is able to mechanically or electronically unlock the door. My guess is that something like this will probably will do the job, but if your neighbors start doing the same thing, there's nothing to keep other cats with a collar from getting in.

A more interesting idea is to use RFID to uniquely identify a particular cat and grant access accordingly. There's a commercial product called Pet Porte that is able to do this with the RFID chip implants that some owners are sticking on their animals these days, but I figure it might be more fun to make your own, perhaps using a tag on a collar.

There are a number of RFID sensors for the Arduino and Basic Stamp microcontrollers. It'd be straightforward to program one of these to accept specific RFID tags and then trip the lock switch in a slightly hacked Cat Mate door. The only problem I see is devising a collar that wouldn't bug the cat and would also place the RFID tag in close enough proximity to the reader. Any readers out there with thoughts on this?

The Flo Control Project - Link
RFID Enabling Your Front Door - Link
Using the Arduino with the Parallax RFID reader - Link

February 3, 2008

Rebuild a Roomba battery

Before you buy a replacement battery for your dead Roomba, you might want to consider rebuilding the pack yourself. You can get a couple of 6 cell Sub-C NIMH packs for less money and more amp hours than the stock battery.

I've been wondering whether it would be economical to just rebuild the battery pack, versus buying a new one. From the looks of it, all it takes is 12 NiMH cells, and from the looks of the case, it looks to be C-Size form factor. For less than $36, I can pick up 12 4500 mAh C cells. I can see iRobot has tried to prevent people from doing this by using TRIANGLE bits for their battery cases, but that's simple to get through.

To remove the triangle bits, just find a small flathead screwdriver that you can wedge in nicely.

Rebuilding a Roomba Battery for Less - Link, Photos

January 23, 2008

Accelerometer motion analysis

There's an article over on the WiiLi Wiki that goes into great detail describing how to translate 3D accelerometer measurements into an estimation of the position, rotation, and velocity of a device like the Wiimote. By making a few assumptions—people's arms have a limited range of motion, most Wii play doesn't take place in moving vehicles, etc.—it's quite surprising what you can get away with with just the accelerometer data.

The amusingly named (but rarely used) term for the rate of change of acceleration is jerk. The jerk term for the remote shows up in the time derivative of the force recorded by the sensor, along with the rotation term that contains the angular velocity of the remote. We can extract both rotation and linear acceleration if we assume a few things:
We know the "up" direction before the motion starts.

Throughout the motion, the jerk on the remote perpendicular to the current direction of gravity is small.

Then we can assume the time derivative of the force component which is perpendicular to our current estimate of the up direction is caused by the user rotating the controller only. This allows us to update our estimate of the up direction for the next time step. In each time step, we can also get the linear acceleration of the remote by subtracting our estimate of from the current force sensor report. In effect we are integrating up a coupled set of ordinary differential equations. (Note, need to review the math here. Beware.)

The main problem with this technique is error accumulation in our estimate of "up." Since it is unlikely the user can keep the controller in constant linear motion without injuring themselves, the TV, or their opponent, we can look for times when the total reported force is close to g = 1.0 to recenter . You have to be careful when doing this because it is possible and probably common for the Wiimote to report an acceleration close to g = 1.0 while it is accelerating. When this happens your acceleration vector does not actually point "up" and you will recenter to an incorrect R. This can happen anytime you are accelerating both downward and in the horizontal plane.

I keep thinking that there should be some class of flying vehicle that, when operated under fairly restrained conditions, might be able to get by with just accelerometer measurements to obtain reasonably accurate state information. You could integrate the acceleration data through very limited motions that are within some margin of error, recalibrate, and repeat. This is probably a pipe dream, but I really want a solution for a $50 6DOF IMU. :/

Accelerometer motion analysis - Link

January 22, 2008

Van Eck phreaking

In 1985, Wim van Eck published a paper which described how the state of a CRT monitor could be reproduced remotely based on the device's electromagnetic radiation. Van Eck or TEMPEST devices, whatever you prefer to call them, aren't just the secret sauce in your favorite science fiction, though for some reason there hasn't been a lot of amateur or open source activity here. I'm not sure why, but I suspect as software radios become more affordable, people will start experimenting more in this space.

There are two open source Van Eck projects that I know of. The first, pictured above, is Erik Thiele's Tempest for Eliza project. By drawing specific black and white patterns on your monitor, Tempest is able to generate audible signals in the AM range. You can use Tempest to play an mp3 file that you can tune in on your radio.

Tempest for Eliza is a fun demo, but what about being able to read someone's monitor remotely?

There's a second open source project, called EckBox, that claims to do just this. By piping the audio from a radio through an 8-bit analog to digital converter, EckBox claims to be able to read this data from a PC parallel port and reproduce the image of an 800x600 monitor. Looking at the code, it seems almost too simple to be true. Likewise, the project hasn't been updated since June 2004 and there aren't many references or screenshots or words of success floating around the net. Anyone with a parallel port and an ADC want to give this a shot and let us know how it works?

Tempest for Eliza - Link
EckBox - Link

Further Reading
Wim van Eck's Paper (PDF) - Link
Compromising Emanations (Markus G. Kuhn, PDF) - Link

January 13, 2008

Arducopter: Arduino helicopter control

A recent Arduino -vs- Basic Stamp discussion over on the DIY Drones site really caught my eye. Jordi makes a nice argument for the Arduino, showing off the current state of his Arducopter, which you can see in the video above. Built using a low cost electric heli, an Arduino board, and the guts from a Wii Nunchuck, his system can currently auto stabilize roll and pitch. More detail and source code are posted at the link below. It's a really great start.

I've also been working on an autonomous helicopter project. While I've been able to build a general game-plan and test a few things with my BS2 controller, I know it's going to be insufficient for the device's needs.

I can say this with a bit of certainty, because I've built a GPS-guided RC car in the past using the BS2. Even with heavy optimization, I used just about all the available memory on the Basic Stamp. There's not much room to read additional accelerometer data and manage the control outputs of even a little 4 channel heli. Long story short, I've got a Boarduino in the mail.

Can a Basic Stamp manage reading and processing accelerometer, compass, and GPS data at the same time? If so, I'd love to hear it, but I'm thinking it'd be difficult to impossible. Don't get me wrong—I love my BS2. It's great for prototyping and quickly building smaller projects. Objectively, though, the Arduino is a little faster, has more ram, and costs much less.

Arducopter - Link
DIY Drones discussion on Arduino versus Basic Stamp for UAVs - Link

January 9, 2008

DIY Arduino on a prototype board

The myriad incarnations of the Arduino are really a testament to the effectiveness of platform standards that are designed around an open hardware, open source model. The Tinkerlog provides us with another example of this with an alternative take on the "breadboardable" Arduino:

A couple of month ago I ordered my first Arduino board. It was one of the Diecimila revision. As I often try something on my breadboard, I found out, that it can get troublesome to connect the Arduino with the breadboard over and over again. Others found that out as well and have solutions for that. An Arduino clone that snaps nicely onto your breadboard, e.g. Boarduino or RBBB.
So what to do if these boards are far away across the ocean and it is holiday season everywhere? You may have guessed it, we build it on a prototype board.

You know you want to make one.

The Tinkerlog post provides a complete howto, complete with the nitty-gritty on programming the bootloader. The project's components are readily available and can be obtained for about $10-15. Of course, this means you should probably make like 10 of them and give some away to friends and coworkers.

Arduino on a prototype board - Link

January 7, 2008

Using the Boarduino with a Wii Nunchuck

Tod E. Kurt put together a nice Boarduino demonstration, connecting the device to the Wii Nunchuck and using it to control the position of a servo. As you rotate the device, the servo continuously adjusts its position to point straight up.

The Boarduino's small footprint made me want to see how small of a device I could whip up in an hour from some fairly complex components. So I decided to see how small the combination of a Boarduino, a Wii Nunchuck, and a hobby servo motor could be. Here's a little video of the result.

His demo is nicely documented and the source is available and extremely digestible. I've been monkeying around with BS2 hardware for too long. This has convinced me it's time to upgrade.

Boarduino, Wii Nunchucks, and Servos - Link
Boarduino: compact, breadboard compatible Arduino clone - Link
Hook your Wii nunchuck up to an Arduino - Link

January 4, 2008

Add Bluetooth to your iPod

fstedie came up with a nice hack for adding internal Bluetooth audio support to your iPod:

1st Ever Bluetooth-Enabled iPod!
If you're like me, you've often asked yourself why Apple has not added native Bluetooth capability to their iPod line up. Even the iPhone only supports mono Bluetooth!

Sure, there are numerous adapters that plug into the iPod's dock connector to give you wireless music, but they are clunky, they come off easily, can't use them with your case and you have to charge them separately!

So, here is my way to add "native" internal Bluetooth support to your 4G iPod. The same method may be used with other iPod versions, I leave that up to you.

The hack essentially involves disassembling a small Bluetooth audio adapter and wiring it directly to the iPod mainboard. Audio input is tapped from the headphone jack and draws power directly from the iPod's battery, giving you a completely wireless and dongle-free audio device.

Check out the picture above, though, and you'll also notice fstedie has replaced the iPod hard disk with a CF card. He has an instructable for that, too. I mentioned Mark Hoekstra's hack to create an iPod-to-CF adapter last year, and it looks like these are now more readily available and can be ordered online. Pretty cool little iPod hacks, I must say.

Add Internal Bluetooth Capability To Your iPod - Link
Convert your 4th Gen iPod to use Flash Memory - Link
iPod CF and SD Card Capability - Link

December 29, 2007

Laser projector

Instructables user echo_anomie posted a nifty howto for creating a very simple portable laser projector. With a bright enough laser, you can project an image across long outdoor distances and there's never any need to adjust focus.

When it's all assembled, you just drop photo slides in the path of the beam and they are projected wherever you have the thing aimed. It'd be interesting to try this with some kind of LCD in place of the slide. This should let you project eerie green videos on skyscrapers around town.

Laser Image Projector - [via] Link

December 27, 2007

Servo hack: make a 360-degree robot drive motor

Servos can work really well as drive motors for a small robot. Their motion is relatively precise and predictable, and they operate on the same voltage as most microcontroller electronics, allowing you to build a simple robot without any additional motor control circuitry.

Standard servos, though, can only rotate through about 180-degrees. Although you can purchase modified servos that will rotate infinitely in either direction, the standard 180-degree servos are more commonly available, are usually cheaper, and you may already have a couple lying around from an old RC car.

Lucky for you, it's pretty easy to modify a servo to rotate infinitely in either direction. Inside your typical analog servo is a small potentiometer that rotates along with the motor output. This acts as a feedback mechanism that controls the position of the motor for a given input pulse rate. Remove this potentiometer along with the mechanical safety stop, and your servo will then rotate in either direction indefinitely. Instead of controlling the position of the servo left or right of neutral, your input PWM signal will now control the motor's speed in either direction (with no motion in the neutral position).

There are two ways of going about this and I've linked to a howto below for both methods.

In the first method, you clip off the mechanical connection to the potentiometer and leave it in place. It stays in the case but doesn't rotate with the output shaft. The bonus to using this method is that you can easily tweak the potentiometer's position to eliminate any motor motion at a neutral state.

The second method involves completely removing the potentiometer and putting a couple of resistors in its place. It's a little more work, but it allows you to slip the potentiometer back in later if you need the standard behavior again. Keep in mind that the mechanical stop will still have been removed, though, so the pot could possibly become damaged if an out-of-range signal is sent to the servo.

Make a 360-degree servo by clipping the potentiometer shaft (video) - Link
Make a 360-degree servo by completely removing the potentiometer - Link

December 26, 2007

Boarduino: compact, breadboard compatible Arduino clone

Boarduino is a "breadboardable" Arduino clone created by Ladyada. It has a much smaller form factor and it's designed to plug right into a solderless breadboard, making your circuit prototyping efforts a breeze. How cool is that?

You use it just like a normal Arduino. You can slap the standard Arduino bootloader on it and run all your normal Arduino sketches. The only major difference is that it doesn't have the USB hardware on-board. Instead, you'll need to use a USB-TTL serial cable ($20 at the Maker store). There is a convenient 6-pin header for this purpose.

The whole thing can be purchased as a kit for $17.50 from the Aadafruit store, making this one of the cheapest Arduino kits available. Check her Boarduino page for details on building, testing and using it.

Boarduino: Solderless Breadboard Arduino Clone - Link
USB TTL Serial Cable - Link

Related:
HOWTO run Arduino on the XO Laptop - Link
Physical computing with the Arduino - Link
Hook your Wii nunchuck up to an Arduino - Link
Arduino-powered holiday lights - Link

December 23, 2007

Johnny Chung Lee's Wiimote hacks

Johnny Chung Lee, who you may recall from $14 steadicam fame (read about it in Make:01), is also a very proficient Wiimote hacker.

His latest, demonstrated in the video above, is a prototype VR system that uses the Wiimote and a head-mounted IR LED as a head tracking device. The software transforms a standard monitor into a 3 dimensional portal. As you move your head, the objects on the screen are positioned appropriately for your new perspective. Think about adjusting your position to see what's around the side of the screen! The effect is like looking through a window, and it gives an more impressive 3D effect that you'd get with the goofy colored glasses.

Lee has a project page for his Wii creations, which also includes a finger tracking, Minority Report-style device and an interactive whiteboard hack. He's generously provided source for all of these hacks. Return the favor by building something cool.

Johnny Chung Lee's Wii Hacks - Link
Procrastineering Blog - Link

December 21, 2007

Essential hacker stocking stuffers

Like most of us, you've probably got some last-minute shopping to take care of. Or maybe there's a special someone in your life who keeps asking you for gift ideas and you need to start dropping hints to avoid another button down and a neck tie. Whatever the reason, here's a quick and dirty hacker gift guide with a variety of gift ideas that should put a smile on someone's face.

Make sure to add your own favorites to the list in the comments area and pass it along. I'm focusing primarily on smaller items that are available in local stores, but feel free to toss in whatever you think is important and shouldn't be missed.

Reading Material:

Make: The Best Of - a killer collection of the best 75 projects from our favorite magazine.
The Dangerous Book For Boys - this is a great book for sharing with your kids. Chock-full of essential information like how to tie knots, play poker, use a compass, build a tree house, and relate to girls.
Knoppix Hacks, 2nd Edition - the swiss army knife for your computer.
Illustrated Guide To Astronomical Wonders - ideal for anyone who's interested in knowing their way around the universe.
Also check out other books from the O'Reilly Hacks Series - Link

Gadgets:

Asus Eee PC - this ultra-tiny Linux laptop is just starting to appear in stores - Hacks
Linksys WRT54GL Router - the L in the GL stands for Linux. It's a $60 router that can be customized to do more than it's thousand dollar big-brothers - Hacks
Western Digital MyBook World Edition External Hard Drive - any extra storage is really nice to have, but this network-available drive contains mirrored RAID storage and a mini Linux computer that can run a web and database server - Hacks
iPhone or iPod Touch - did I really put that here? - Hacks
Broadband Mobile Card from Verizon or Sprint - they are getting super
popular, and heck, they are cheaper than an iPhone.
Nokia N95-3 - the winner of our most hackable mobile phone survey - Hacks

Toys:

Air Hogs Havoc Heli Laser Battle - remember the Picco-Zs and their clones from last year? Here's two of them in a single package, enhanced with a trigger that let's you zap your friend's heli down.
E-Sky Lama V4 Helicopter- Yeah, I'm crazy for helicopters right now. The counter-rotating models like this one are about $100, ready (and easy) to fly, and very hackable.
WowWee RoboSapien V2 - fun for the kids. More fun with a soldering iron - Hacks

Gear:

2GB or larger micro SD card, plus various SD and USB adapters - perfect for scooting files around, the size of a finger nail, and you can put a full Linux distro, anti virus software, or a Puppy Linux virtual machine on it - Hacks
Mini Multimeter - always handy.
Bike Multitool - a good one will pack allen and hex wrenches, screw drivers, and a knife into a pretty small package. Perfect for voiding warrantees in a pinch. Oh, and there's a chain tool, too - Link, Link
Soldering Tools - whether it's a new Weller or just a pair of helping hands, it'll be welcome in any stocking - Link, Link

What have we missed here? Add your wishes to the comments. Then find a completely non-tacky way to get this list into the hands of someone who wants you to be a happy hacker.

December 16, 2007

HOWTO - DIY radio modem

Eric Seifert sent in some information on creating a home brew radio modem using a standard PC sound card, an iPod FM transmitter, and an FM radio. He has his current revision working at 9600 BAUD for distances in the neighborhood of hundreds of feet.

The sending side outputs an amplitude encoded data stream to the sound card, which is connected to the FM transmitter. On the receiving end, an FM radio receives the transmission, and outputs it to the receiving soundcard's line-in, where it is then decoded. The hardware set up is extremely simple. It's the software for reliably encoding and decoding the data (and handling error conditions) that's the tricky part.

Eric released some example encoding/decoding software on his site, so you can start with that and take a swing at improving its error handling ability. You'll need a Linux box with the ALSA and SDL libraries to compile it.

Radio Modem - Link

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