Hack Together Your Own Bat Signal

July 11, 2020 by Orlando Hoilett 27 Comments

Bats use echolocation to see objects in front of them. They emit an ultrasonic pulse around 20 kHz (and up to 100 kHz) and then sense the pulses as they reflect off an object and back to the bat. It’s the same type of mechanism used by ultrasonic proximity sensors for object-avoidance. Humans (except perhaps the very young ones) can’t hear the ultrasonic pulses since the frequency is too high, but an inexpensive microphone in a simple bat detector could. As it turns out bat detectors are available off the shelf, but where’s the fun in that? So, like any good hacker, [WilkoL] decided to build his own.

[WilkoL’s] design is composed primarily of an electret microphone, microphone preamplifier, CD4040 binary counter, LM386 audio amplifier, and a speaker. Audio signals are analog and their amplitudes vary based on how close the sound is to the microphone. [WilkoL] wanted to pick up bat sounds as far away as possible, so he cranked up the gain of the microphone preamplifier by quite a bit, essentially railing the amplifiers. Since he mostly cares about the frequency of the sound and not the amplitude, he wasn’t concerned about saturating the transistor output.

The CD4040 then divides the signal by a factor of 16, generating an output signal within the audible frequency range of the human ear. A bat signal of 20 kHz divides down to 1.25 kHz and a bat signal of up to 100 kHz divides down to 6.25 kHz.

He was able to test his bat detector with an ultrasonic range finder and by the noise generated from jingling his keychain (apparently there are some pretty non-audible high-frequency components from jingling keys). He hasn’t yet been able to get a recording of his device picking up bats. It has detected bats on a number of occasions, but he was a bit too late to get it on video.

Anyway, we’re definitely looking forward to seeing the bat detector in action! Who knows, maybe he’ll find Batman.

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Contactless Doorbell Built To Avoid Coronavirus

June 4, 2020 by Lewin Day 15 Comments

It’s often said that necessity breeds creativity, and during a global pandemic such words have proved truer than ever. Realising the common doorbell could be a potential surface transmission point for coronavirus, [CasperHuang] whipped up a quick build.

The build eschews the typical pushbutton we’re all familiar with. Instead, it relies on an ultrasonic distance sensor to detect a hand (or foot) waved in front of the door. An Arduino Leonardo runs the show, sounding a buzzer when the ultrasonic sensor is triggered. In order to avoid modifying the apartment door, the build is housed in a pair of cardboard boxes, taped to the base of the door, with wires passing underneath.

It’s a tidy way to handle contactless deliveries. We imagine little touches like this may become far more common in future design, as the world learns lessons from the COVID-19 pandemic. Every little bit helps, after all. Video after the break.

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Ultrasonic Sound Gun Precisely Aims Your Music

April 30, 2020 by Moritz v. Sivers 25 Comments

When listening to music you sometimes cannot avoid the situation where other people get annoyed because they feel it disrupts their important doings or they do not share your taste in avant-garde doom metal. Of course one could just use headphones. But a hackier way would be to build a parametric speaker that focuses soundwaves into a narrow beam like [Shane] did with this ultrasonic sound gun.

As the directivity of a soundwave depends on the size of the source and its frequency, a directed beam can practically only be achieved with ultrasound. Even though we are not able to perceive frequencies above ~20 kHz, the nonlinear properties of air make it possible to hear the audio modulated onto an ultrasonic carrier signal. For his sound gun [Shane] was inspired by another parametric speaker project. It took him some time to get the 555 timer circuit oscillating at the right frequency and he fried a cheap Bluetooth audio module while trying to increase the output volume but in the end, he managed to get everything working. As the project name suggests, he also 3D printed a gun-shaped enclosure. The video below shows that the sound from the gun behaves really similar to a beam of light and can, for example, be bounced off other objects.

If you are looking for other inspiration there is a whole list of cool ultrasonic projects from distance sensors to acoustic levitation.

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Slippy Slapper Uselessly Uses All The Arduinos

March 13, 2020 by Kristina Panos 8 Comments

Want to take that annoyingly productive coworker down a notch? Yeah, us too. How dare they get so much done and be so happy about it? How is it possible that they can bang on that keyboard all day when you struggle to string together an email?

The Slippy Slapper is a useless machine that turns people into useless machines using tactics like endless distraction and mild physical violence. It presses your buttons by asking them to press buttons for no reason other than killing their productivity. When they try to walk away, guess what? That’s another slappin’. Slippy Slapper would enrage us by proxy if he weren’t so dang cute.

You’re right, you don’t need an Arduino for this. For peak inefficiency and power consumption, you actually need four of them. One acts as the master, and bases its commands to the other three on the feedback it gets from Slippy’s ultrasonic nostrils. The other three control the slappin’ servos, the speakers, and reading WAV files off of the SD card. Slap your way past the break to see Slippy Slapper’s slapstick demo.

Need to annoy a group of coworkers all at once? Slip a big bank of useless machines into the conference room while it’s being set up.

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Death To All Coca Cola Cans With This Miniature Arduino Powered Cannon

December 8, 2019 by Gerrit Coetzee 8 Comments

[MJKZZ] sends in this entertaining little tutorial on building a small automated cannon out of a syringe.

He starts the build off by modifying an arc lighter, the fancy kind one might use to light a fire on a windy day, so that it can be controlled by a micro-controller. The arc is moved to the needle end of the syringe with a careful application of wires and hot glue. When the syringe is filled with a bit of alcohol and the original plunger is pressed back in a small spark will send it flying back out in a very satisfying fashion.

Of course it wouldn’t be a proper hack without an Arduino added on for no reason other than the joy of doing so. [MKJZZ] adds an ultrasonic sensor into the mix which, when triggered appropriately by an invading object fires the arc lighter using a reed relay.

He demonstrates the build by eliminating an intruding coke can on his work bench. You can see it in the video after the break. All in all a very fun hack.

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Behold A 3D Display, Thanks To A Speeding Foam Ball

November 19, 2019 by Donald Papp 15 Comments

We’ve seen 3D image projection tried in a variety of different ways, but this is a new one to us. This volumetric display by Interact Lab of the University of Sussex creates a 3D image by projecting light onto a tiny foam ball, which zips around in the air fast enough to create a persistence of vision effect. (Video, embedded below.) How is this achieved? With a large array of ultrasonic transducers, performing what researchers call ‘acoustic trapping’.

This is the same principle behind acoustic levitation devices which demonstrate how lightweight objects (like tiny polystyrene foam balls) can be made to defy gravity. But this 3D display is capable of not only moving the object in 3D space, but doing so at a high enough speed and with enough control to produce a persistence of vision effect. The abstract for their (as yet unreleased) paper claims the trapped ball can be moved at speeds of up to several meters per second.

It has a few other tricks up its sleeve, too. The array is capable of simultaneously creating sounds as well as providing a limited form of tactile feedback by letting a user touch areas of high and low air pressure created by the transducers. These areas can’t be the same ones being occupied by the speeding ball, of course, but it’s a neat trick. Check out the video below for a demonstration.
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