X-Band linear rail SAR imaging

[Greg Charvat] really wanted high resolution X-Band linear rail SAR imaging system. He wanted it bad enough to scrounge through parts at HAM radio swap meets until he had the bits to build one himself. The unit is used to take high resolution radar imaging. For example, the image above is constructed of push pins behind a foam wall. The synthetic aperture radar system came in at roughly  $250. Not bad at all. You may have to dig through the links a bit to find the build information. Be sure to check out the hardware gallery and the schematics(pdf).

[via Makezine]

Student Soaker, wireless water gun

As far as pranks go, [Austin Shaf's] wireless hidden water gun is a real treat. The video above goes over a brief explanation and shows the setup in action. The prankster holds onto a wireless AVR remote, and when the unsuspecting victim walks by, he activates a second AVR controlling a pump; spraying water everywhere.

While most of us are out of school by now, the project would still be a fun office or perhaps street prank. If you’re one for registering, schematics and source code can be found at AVRFreaks. Alternatively, check after the jump for a copy of both.

Related: Office Pranks, and Water Guns.

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The PR2 calls the shots

Can you beat this robot at pool? This sparks something of a “let the wookie win” attitude for us, but we still love to watch the video. This is the PR2 playing pool thanks to the folks over at the Willow Garage. It uses a laser sensor to detect the legs of the pool table, and cameras to find the diamonds and balls at the playing surface rather than using an overhead camera. They cut down on the coding work needed by using FastFiz, an open source Billiards physics library. The final step was building an interface so the robot could use a cue. Check it out after the break (no pun intended).

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Replacement speedometer

[Howard] built his own replacement speedometer for his truck after the original speedometer cable broke. He’s using surface mount components and produced a two-board design that is quite nice. When he tipped us off he mentioned that this is Arduino powered and uses a hall effect sensor. There’s not talk of this in his writeup but we gather that he’s just using the bootloader on an AVR chip and that he hall effect sensor measures the rotation of one of the wheels. When the vehicle isn’t moving the board alternates between max speed and trip distance. Once he’s on the roll it shows current speed.

Building a cluster of iPaq PCs

[Steven Pigeon] got his hands on ten iPaq computers that a friend acquired through an eBay auction. The older machines were in good condition but the march of technology had left them behind as casualties. He’s given them new life by assembling a cluster. The first order of business was testing the hardware to make sure it’s working. [Steven] used memtest86+ that comes along with the Ubuntu distribution of Linux to find one bad memory chip in the bunch (a revelation that took 10 hours to discover on the slow hardware). He assembled the unit above with MDF as a support structure and threaded rod to hang the boards. He ended up with a beautiful module and his next step is to choose the operating system that will pull the whole thing together.

We find this build every bit as beautiful as the file cabinet cluster. It’ll be interesting to check back with him and see what kind of performance he can get out of it.

No nonsense mbed development demo

This tweeting RFID reader is a great working example for the mbed. When an RFID tag is read it is matched with the name of the owner and a Twitter message is sent out. This is very similar to the RFID cat tracker that used an Arduino.
The code is short and simple due to the use of available mbed libraries. The hardware needs just two extra modules, an RFID reader and an Ethernet socket. If you’re trying to decide if you can make the jump over to ARM development this certainly presents an easy learning curve and an opportunity to get comfortable with the code and the libraries before you make a purchase. It’s also a great set of test code to start with if you have an mbed and the two supplementary modules on hand. The quick video clip after the break will walk you through the components and the code.
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