Ping pong ball barrage

What should you do with your down time between sophomore and junior year at MIT? You better build something awesome. [Christian Reed] didn’t disappoint with his newest creation. He calls it the Ping Pong Mauler and we think that’s an appropriate name. It doesn’t just lunch a ball, it belches forth a relentless barrage.

He certainly has no shortage of ammo. A few garbage bags full of the white orbs number at least 3000 strong, and the plastic drum he’s using as a hopper has room for them all. Jamming is an issue and in the image above you can see him working the agitator with his right hand to prevent a clog. The system is mobile, but the shop vacuum used to propel the balls needs AC power. This means there is a tether that keeps it from roaming too far from home. [Christian] included an air tank in the design but apparently the pressurized air doesn’t do much to help with launch speed. That’s good because pressurized ball guns can be scary.

Check out the video after the break to see the ping pongs fly. We bet they’ll be mowing over some strays out in the yard for at least the rest of this summer.

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Magic clock locates your friends

Just like the clock from Harry Potter, a team of media informatics students at the University of Munich built a grandfather clock that doesn’t keep track of time; instead, it keeps track of where everyone is, whether it be their university, work, or in prison.

The build uses Android and iOS apps on each team member’s cell phone to send their current location to a web server. A circuit built inside an old grandfather clock the team picked up from eBay communicates with the web server through a WiFly Shield to control a quartet of servos and drive the clock hands.

Because the grandfather clock only came with two clock hands, the team used a series of four concentric shafts to move each hand around the dial. With a bit of clever gear fabrication on their laser cutter, they were able to use unmodified servos move the hands all the way around the clock.

The avatars on the tip of each clock hand are the remains of decapitated LEGO minifigs, a choice that makes sense after viewing the build video available after the break.

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Getting connected with your home security system

This simple device, paired with some creating code will let you become your own home security monitoring service. It’s called the PhantomLink and [Adam] started the project as a commercial venture. He recently decided to go open source with the hardware and will soon be posting a guide on how to program your own web interface too.

We just looked in on a project which takes control of a security panel using an Arduino. The PhantomLink is focused on not just reusing the input hardware, but monitoring the whole system. It sounds like several different protocols are supported.

The DB9 jack is intended for use with an adapter you can wire yourself. Basically just tap into the terminal block on the alarm controller for your house, then route those connections to the proper pins. A PIC 12F683 monitors the alarm system, pushing data via the WiFi module mounted on the board. With that web connection you can do anything you want by catching and formatting the data.

Hackathon results in the Facebook book

[Jeremy Blum] and [Jason Wright] pose with their project at the end of a 24 hour hackathon. The Facebook headquarters in New York City held the event as part of their Summer of Hack program. As an homage to the hosts, the hacking duo decided to create a physical book and populate it with the virtual Facebook. And what do you call such a creation? The Face(book)^2.

The video after the break gives the best overview of the hardware, but here’s the gist of it: They started with the largest hardcover book they could find, hollowing out its pages to house their own hardware. When you open the book it calls back to a computer over an Xbee link with a request for data. The python script on the computer pulls the newest from a Facebook feed, sending it back to the book to be displayed. There is a graphic LCD and four character LCDs built in for this purpose. There’s also an accelerometer which is used for detecting page turns when the cover is jostled. The rest of the interactivity is provided by a few tactile switches mounted next to the smaller LCD screens for navigation and the ‘like’ feature.

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Mechanical relay logic that was snubbed for a microcontroller

[Alex] was tasked with a control design problem for a set of motors. The application called for the back of a truck to open up, some 3D scanning equipment to rise from its enclosure, and finally the equipment needed to rotate into place. All of this needed to happen with one flip of a switch, then proceed in reverse when the switch was turned off. We can understand why the final design used a microcontroller, but we also think that [Alex's] relay logic circuit is an eloquent way of doing things.

He uses limiting switches as the feedback loop for the logic. In the video after the break he walks us through the schematic. Each of the three motors has an up and down limiting switch. These control the three relays which switch power to the motors. We like the design because interrupting the movement mid-operation provides no problem for the system. The only real issue we see is that relays wear out, and the automotive application of the hardware may cause this to happen more quickly than normal.

You may recognize the clear gears used in the demo. [Alex] previously showed us how he makes those.

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Understanding op-amps from simple to hard

[Tim] wanted to help out a ECE student struggling with some Op-Amp problems. He put together a video which does a good job of explaining what an Op-Amp does, then tackles each of the questions one at a time.

His analogy is illustrated in this image. There’s an operator using a crane to lift a crate. He is watching a ‘radio man’ in a window of the building to know how high it should be lifted. These roles are translated to the function of an Op-Amp in a way that makes understanding the common parts quite easy. The crane is the Op-Amp and the floor to which it is trying to lift the crate is the input pin. The current height of the crate is the output signal. The radio man is the feedback resistor which is trying to get the desired height and current height to equal each other. Watch the video after the break and all becomes clear.

After this analogy is explained [Tim] tackles the actual homework problems. He’s going through everything pretty quickly, and doesn’t actually give the answers. What he does is show how this — like most circuit solving problems — depends on how you group the components in order to simplify the questions. Grab a pen and paper and put on your electron theory hats to see if you can solve the questions for yourselves.

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Recovering from a Seagate HDD firmware bug

Hard drive firmware is about the last place you want to find a bug. But that turned out to be the problem with [BBfoto's] Seagate HDD which he was using in a RAID array. It stopped working completely, and he later found out the firmware has a bug that makes the drive think it’s permanently in a busy state. There’s a firmware upgrade available, but you have to apply it before the problem shows its face, otherwise you’re out of luck. Some searching led him to a hardware fix for the problem.

[Brad Garcia] put together the tutorial which illustrates the steps needed to unbrick the 7200.11 hard drive with the busy state bug. The image in the lower right shows the drive with a piece of paper between the PCB and the connectors which control the head. This is necessary to boot the drive without it hanging due to the bug. From there he issues serial commands to put it into Access Level 2, then removes the cardboard for the rest of the fix.

In the tutorial [Brad] uses a serial-TTL converter. [BBfoto] grabbed an Arduino instead, using it as a USB-ttl bridge.

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