These greeting cards must be the product of a mechanical engineer run amok. They come with a crank and are designed to entertain with their simple, yet elegant movements. [Thanks Phil]

Magnetic card stripe reader

[JP] built an Arduino based magnetic card reader. It uses off-the-shelf parts but if you don’t mind buying the components this will get you up and running in no time. If you want more info there’s also this Teensy based version.

Homemade Airsoft sentry gun

This sentry gun has an amazingly fast firing rate that can continue for quite a while, thanks to the big flashlight housing that is holds a lot of ammo. [Thanks David]

Scanner easter egg

The engineers over at HP had a little fun building an easter egg into this scanner. If you know what you’re doing you can get it to play the Ode to Joy. It needs to join the old-hardware band from our Links post earlier in the month. [Thanks Googfan]

With exams behind him [Adam Greig] had time to make a Nerf sentry gun. It’s actually quite easy to pull everything together. He’s got a netbook running Motion, an open source motion sensing program for use with a webcam. When movement is detected an Arduino, connected via a USB cable, actuates a servo to pull the trigger of the gun. The turret itself has seen a battery upgrade that increases the firing speed. It’s fun to see hardware prototyping done with a few pencils and a fist full of cable ties. Check it out after the break.

This particular toy, the Nerf N-Strike Vulcan, has become quite a popular starting point for turrent projects. We’ve seen one that uses a motorized base, and another that was part of a final project at Cornell.

[John Park] is documenting his build of a Nerf Sentry gun. So far, he’s rigged the trigger and set up the motorized base. He’s documenting the process in fantastic detail with great photos along the way. If you want to see what it will be like when it is finished, check out these other Nerf sentry guns that we’ve featured in the past.

Reader, [Ben Godding], sends in the video for his senior design team’s automated paintball sentry. The frame is made of plasma cut aluminum. The paintball gun uses a custom hopper mounted remotely from the gun body. It has two webcams offering a 160 degree field of vision, and the image processing is done by a dual core pentium CPU booting windows xp off a compact flash card. The computer interfaces with the 1/4scale RC servos using a PIC24. The paintball sentry can either be configured via a computer GUI when a monitor is available or a baclkit keypad and 4×20 charachter display in the field.

Related: [Jared Bouck]‘s paintball gun turret

[Jared Bouck] has been sending in his projects for a couple years now. We’ve enjoyed his heavy-duty DDR pads, LCD backlight repair, and ion cooling projects. His latest, an RC paintball gun turret, is our favorite though. He actually rates this as one of the easier projects he’s published; it just took a while to assemble. Several design decisions were made to keep the project simple. Two 32 Degrees Icon-E paintball guns were used. The guns already have electric solenoids for firing, so a special trigger mechanism didn’t have to be fashioned. Q-loaders were used to prevent any ball feed problems. The motors, driver boards, and RC components are all borrowed from combat robots for reliability. He’s hoping to produce a small number of kits based on this design.

Related: We’ve got quite a few sentry gun projects in the archive.

We’ve seen plenty of turrets before, but this one really excels in design. It features two webcams for more precision detection and tracking and when set to manual mode, it can be controlled with an XBox 360 controller. He’s posted great pictures of the process with a step by step break down. Tons of useful links are included to help you out.

Someone should construct a Portal sentry gun case for this thing and add voice clips.