Meowing Box Will Befuddle Your Friends

If you don’t own a cat, hearing the sound of one meowing from somewhere in the house probably comes as quite a shock. The Cat Prank box built by [Reuben] promises to deliver such hilarity with aplomb. 

The idea is simple: hide the Cat Prank box in a cupboard or other space in a friend’s house, and it will meow from its secret location. When found, either the light sensor or motion sensor will trigger the yowling of an angry feline, with hopefully startling effects.

An Arduino Mini is the brains of the operation, paired with an XY-V17B sound module which plays the required animal wailings. There’s also a 433 MHz radio module that lets the prankster trigger meowing via remote control.

Code is available for those wishing to build their own. We’d love to see a mod with a time delay built in, so the device could be hidden and left to start meowing at some later date when the prankster is far away.

Similar work has graced these pages before, like the devilishly fiendish OpenKobold design. Just make sure your friends are receptive to such jokes before you go ahead and invest time and hardware in the prank!

Love Open Source But Hate People? Get OpenKobold

[Tadas Ustinavičius] writes in to tell us of his latest project, which combines his two great loves of open source and annoying people: OpenKobold. Named after the German mythical spirit that haunts people’s homes, this tiny device is fully open source (hardware and software) and ready to torment your friends and family for up to a year on a CR1220 battery.

The design of the OpenKobold is quite simple, and the open source nature of the project makes this an excellent case study for turning an idea into a fully functional physical object.

Beyond the battery and the buzzer module, the OpenKobold utilizes a PIC12F675, a transistor, and a few passive components. This spartan design allows for a PCB that measures only 25 x 20 mm, making it very easy to hide but fiendishly difficult to try to track down later on.

But the real magic is in the software. The firmware that [Tadas] has written for the PIC not only randomizes how often the buzzer goes off, but how long it will sound for. This makes predicting the OpenKobold with any sort of accuracy very difficult, confounding the poor soul who’s searching their home or office for this maddening little device.

Hackers have a long and storied history of creating elaborate pranks, putting the OpenKobold in very good company. From randomly replaying signals from a remote control to building robotic cardboard burglars, we’ve seen our fair share of elaborate pranks from the community.

Rickroll The Masses With A Coin Cell Throwie

If there is one educational institution that features on these pages more than any other, it may be Cornell University. Every year we receive a pile of tips showing us the engineering term projects from [Bruce Land]’s students, and among them are some amazing pieces of work. Outside the walls of those technical departments though, we suspect that cool hacks may have been thin on the ground. English Literature majors for example contain among their ranks some astoundingly clever people, but they are not known for their handiness with a soldering iron or a lathe.

We’re happy to note then that someone at Cornell who is handy with a soldering iron has been spreading the love. In the form of coin cell powered throwies that intermittently Rickroll the inhabitants of the institution’s halls of residence. We have few technical details, but they seem to be a simple affair of a small microcontroller dead-bug soldered to a coin cell and a piezoelectric speaker. If we were embarking on such a project we’d reach for an ATtiny of some description, but similar work could be done with a PIC or any number of other families.

The Cornell Daily Sun write-up is more a work of investigative journalism detailing the perplexed residents searching for the devices than it is one of technical reference. We’re pleased to note that the university authorities have a relaxed attitude to the prank, and that no action will be taken against the perpetrator should they be found.

Thus we’d like to take a moment to reach out to the Cornell prankster, and draw their attention to our Coin Cell Challenge competition. There is still time to enter, and a Rickrolling throwie would definitely qualify. This isn’t the first tiny Rickrolling prank we’ve shown you on these pages.

Thanks [Simon Yorkston] for the tip.

How To Put A Jag On Your School Roof

Did you ever commit any pranks in your time at high school, college, or university? Maybe you moss-painted a rude word on the wall somewhere, or put a design in a sports field with herbicide, or even worse, slow-release fertiliser. [Roman Kozak] and his friends went far further than that last summer when they replicated some of the most famous student pranks; they put a Jaguar S type car on the roof of their school. And now the dust has settled, he’s posted an account of how they did it.

jag-on-roof-guy-cuttingOf course, putting a car on the roof is a significant challenge, particularly when you only have the resources of a high-school student. Ensuring the roof was strong enough for a car, and then hiring a crane to do the deed, was beyond them. They therefore decided to take the wheels and outer body panels of a car and mount them on a wooden frame to give the appearance of a car.

They needed a statement vehicle and they didn’t have a huge budget, so it took them a while to spot a for-parts Jaguar S type which when it came into their possession they found only had a fault with its reverse gear. Some hard work removed the panels, and the rest of the car was taken for scrap.

Frenetic work as the term end approached gave them their frame, and a daring midnight raid was mounted to winch the parts to the roof with a pulley. The result was so popular with their classmates and teachers that they owned up to the prank rather than preserve their anonymity. We think these young scamps will go far.

This is definitely the first car-on-roof prank we’ve brought you on Hackaday, but it’s not the first to be done. [Roman] and his friends cited an MIT prank as their inspiration, but the daddy of car-on-roof stunts has to go to Cambridge University students in the 1950s. Their Austin might be a lot smaller than the MIT Chevy or [Roman]’s Jag, but they got it onto their roof in one piece as a full car rather than a facsimile of one.

Important note: The author would like to state for the record that she and her friends were somewhere else entirely and had solid alibis when in summer 1993 the logo of Hull University Union Technical Committee appeared in the lawn outside Hull University Union. We’re sure that commenters will be anxious to set their own records straight for posterity in a similar manner.

Awesome Prank Or Circuit-Breaker Tester?

Many tools can be used either for good or for evil — it just depends on the person flipping the switch. (And their current level of mischievousness.) We’re giving [Callan] the benefit of the doubt here and assuming that he built his remote-controlled Residual Current Device (RDC) tripper for the purpose of testing the safety of the wiring in his own home. On the other hand, he does mention using it to shut off all the power in his house during an “unrelated countdown at a party”. See? Good and evil.

An RCD (or GFCI in the States) is a kind of circuit breaker that trips when the amount of current in the hot and neutral mains power lines aren’t equal and opposite, which would suggest that the juice was leaking out somewhere, hopefully not through someone. They only take a few milliamps of imbalance to blow so that nobody gets hurt. Making a device to test an RCD is easy; a resistor between hot and the protective ground circuit would do.

[Callan] over-engineers. He used a 50 W resistor where 30 W would do under the worst circumstances. A stealthy solid-state relay switches the resistor in, driven by an Uno and a Bluetooth module, so he can trip his circuit breakers from his smartphone, naturally.
Continue reading “Awesome Prank Or Circuit-Breaker Tester?”

Never Gonna Give Up Free WiFi

Our conscience almost prevented us from posting this one. Almost.

What do people all around the world want most? Free WiFi. And what inevitable force do they want to avoid most, just after death and taxes? Rick Astley. As a getting-started project with the ESP8266, user [jaime] built a “free WiFi portal” that takes advantage of people’s deepest desires. Instead of delivering sweet, high-bandwidth connectivity, once you click through the onerous terms and conditions, it delivers you a looped GIF with background music.

And all of this on $4 worth of hardware, with firmware assembled in the cloud and easily available to anyone. We live in a truly frivolous glorious age.

Digging through our archives, we found a number of Rickroll posts that we’d rather forget, but this steam-powered record player bears a second look.


Annoy Your Enemies With The Hassler Circuit

[Craig] recently built himself a version of the “hassler” circuit as a sort of homage to Bob Widlar. If you haven’t heard of Bob Widlar, he was a key person involved in making analog IC’s a reality. We’ve actually covered the topic in-depth in the past. The hassler circuit is a simple but ingenious office prank. The idea is that the circuit emits a very high frequency tone, but only when the noise level in the room reaches a certain threshold. If your coworkers become too noisy, they will suddenly notice a ringing in their ears. When they stop talking to identify the source, the noise goes away. The desired result is to get your coworkers to shut the hell up.

[Craig] couldn’t find any published schematics for the original circuit, but he managed to build his own version with discrete components and IC’s. Sound first enters the circuit via a small electret microphone. The signal is then amplified, half-wave rectified, and run through a low pass filter. The gain from the microphone is configurable via a trim pot. A capacitor converts the output into a flat DC voltage.

The signal then gets passed to a relaxation oscillator circuit. This circuit creates a signal whose output duty cycle is dependent on the input voltage. The higher the input voltage, the longer the duty cycle, and the lower the frequency. The resulting signal is sent to a small speaker for output. The speaker is also controlled by a Schmitt trigger. This prevents the speaker from being powered until the voltage reaches a certain threshold, thus saving energy. The whole circuit is soldered together dead bug style and mounted to a copper clad board.

When the room is quiet, the input voltage is low. The output frequency is high enough that it is out of the range of human hearing. As the room slowly gets louder, the voltage increases and the output frequency lowers. Eventually it reaches the outer limits of human hearing and people in the room take notice. The video below walks step by step through the circuit. Continue reading “Annoy Your Enemies With The Hassler Circuit”