Dual Sensor Echo Locator Gives High Accuracy at Low Cost

Infrared certainly has its uses, but if you’re trying to locate objects, ultrasonic detection is far superior. It’s contact-less, undetectable to the human ear, and it isn’t affected by smoke, dust, ambient light, or Silly String.

If you have one ultrasonic sensor and a microcontroller, you can detect plenty of useful things, like the water level in a rain barrel or the distance traveled by a tablet along a rail. If you have two sensors and a microcontroller, you can pinpoint any object within a defined range using trigonometry.

[lingib]’s dual sensor echo locator uses two HY-SRF05s, but the cheap and plentiful HC-SR04s will work, too. Both sensors are arranged for maximum beam overlap and wired up to an Arduino Uno. One sensor’s emitter is blocked with masking tape, so all it does is listen.

When the system registers the object, it shows up as a red dot on a grid inside a Processing sketch along with a bunch of details like the object’s coordinates, its distance from each sensor, and the area of the triangle formed by the two sensors and the object. [lingib] reports that the system is quite accurate and will work for much larger playgrounds than the 1 meter square in the demo after the break.

Don’t want to detect objects? Ultrasonic sensors are cheap enough to hack into other things, like this one-way data communications module.

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Turning That Old Hoverboard Into A Learning Platform

[Isabelle Simova] is building Hoverbot, a flexible robotics platform using Ikea plastic trays, JavaScript running on a Raspberry Pi and parts scavenged from commonly available hoverboards.

Self-balancing scooters a.k.a. Hoverboards are a great source of parts for such a project. Their high torque, direct drive brushless motors can drive loads of 100 kg or more. In addition, you also get a matching motor controller board, a rechargeable battery and its charging circuit. Most hoverboard controllers use the STM32F103, so flashing them with your own firmware becomes easy using a ST-link V2 programmer.

The next set of parts you need to build your robot is sensors. Some are cheap and easily available, such as microphones, contact switches or LDRs, while others such as ultrasonic distance sensors or LiDAR’s may cost a lot more. One source of cheap sensors are car parking assist transducers. An aftermarket parking sensor kit usually consists of four transducers, a control box, cables and display. Using a logic analyzer, [Isabelle] shows how you can poke around the output port of the control box to reverse engineer the data stream and decipher the sensor data. Once the data structure is decoded, you can then use some SPI bit-banging and voltage translation to interface it with the Raspberry Pi. Using the Pi makes it easy to add a cheap web camera, microphone and speakers to the Hoverbot.

Ikea is a hackers favourite, and offers a wide variety of hacker friendly devices and supplies. Their catalog offers a wide selection of fine, Swedish engineered products which can be used as enclosures for building robots. [Isabelle] zeroed in on a deep, circular plastic tray from a storage table set, stiffened with some plywood reinforcement. The tray offers ample space to mount the two motors, two castor wheels, battery and the rest of the electronics. Most of the original hardware from the hoverboard comes handy while putting it all together.

The software glue that holds all this together is JavaScript. The event-driven architecture of Node.js makes it a very suitable framework to use for Hoverbot. [Isabelle] has built a basic application allowing remote control of the robot. It includes a dashboard which shows live video and audio streams from the robot, buttons for movement control, an input box for converting text to speech, ultrasonic sensor visualization, LED lighting control, message log and status display for the motors. This makes the dashboard a useful debugging tool and a starting point for building more interesting applications. Check the build log for all the juicy details. Which other products from the Ikea catalog can be used to build the Hoverbot? How about a robotic Chair?

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AM Ultrasonic Transmitter And Receiver

Most often ultrasonic transducers are used for distance measurements, and in the DIY world, usually as a way for robots to detect obstacles. But for a weekend project, [Vinod.S] took the ultrasonic transmitter and receiver from a distance-meter module and used amplitude modulation to send music ultrasonically from his laptop to a speaker, essentially transmitting and receiving silent, modulated sounds waves.

The transmitter and receiver
The transmitter and receiver

For the transmitter, he turned an Arduino Pro Micro into a USB sound card which he could plug into his laptop. That outputs both the audio signal and a 40 kHz carrier signal, implemented using the Arduino’s Timer1. Those go to a circuit board he designed which modulates the carrier with the audio signal using a single transistor and then sends the result out the ultrasonic transmitter.

He took care to transmit a clear signal by watching the modulated wave on an oscilloscope, looking for over-modulation and clipping while adjusting the values of resistors located between the transistor, a 5 V from the Arduino and the transmitter.

He designed the receiver side with equal care. Conceptually the circuit there is simple, consisting of the ultrasonic receiver, followed by a transistor amplifier for the modulated wave, then a diode for demodulation, another transistor amplifier, and lastly a class-D amplifier before going to a speaker.

Due to the low 40 kHz carrier frequency, the sound lacks the higher audio frequencies. But as a result of the effort he put into tuning the circuits, the sound is loud and clear. Check out the video below for an overview and to listen to the sound for yourself. Warning: Before there’s a storm of comments, yes the video’s shaky, but we think the quality of the hack more than makes up for it.

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Hackaday Prize Entry : DEER — An Electronic Repellent

Ultrasonic repellent devices used to keep away insects, rodents, birds, and even large animals have been around for quite a while, but their effectiveness depends on who you ask.  Some critters just don’t seem affected, while some others definitely will avoid being around such a device. Deploying a few of these devices to scare off animals seems to be working quite well for [Ondřej Petrlík]. Around where he lives, the fields of tall grass need to be mowed down during the spring. Unfortunately, the tall grass is ideal for young, newborn animals to stay hidden and safe. The mowing machines would often cripple and hurt such animals, and [Ondřej] desperately wanted to solve the problem and prevent these mishaps.

He built an electronic repeller to keep away wild animals and their young from his farm/ranch/range back in the Czech Republic. He used an Arduino Mini to drive a large piezo transducer to scare away the wild animals from the vicinity of the device. He likely used a high enough frequency beyond human range, but we’ll know more when he publishes his code and details. There are also a few large 10mm LED’s – either to visually locate the device or help drive the animals away in conjunction with the ultrasound, with an LDR that activates the LEDs at night. Using the Arduino helps to turn on the transducer at random intervals, and hopefully, he is using a range of different frequencies so the animals don’t become immune to the device.

His first prototype was cobbled together using vanilla, off the shelf parts. An Arduino, a step up converter, an LDR, a couple of LEDs, a reed switch for powering it on via a magnet, and a large ultrasonic transducer, all powered by three alkaline AA batteries. He stuffed it all inside a weatherproof molded enclosure, holding it all together with a lot of hot glue. This didn’t make it very rugged for the long-term, outdoor field use. While the prototype worked well, he needed several of the devices to be placed all around his farm. To make assembly easy and make it more reliable, he designed a custom PCB to fit in the weather proof enclosure. This allowed him to easily mount all the required parts for a more reliable result. His project is still a work in progress, so if you have worked with these types of ultrasonic repellent devices to keep away animals, and have any insights that may help him, do chime in with your comments. [Ondřej] seems pretty satisfied with the results so far.

A Cool Mist that Dries Your Clothes

This one is both wild enough to be confused as a conspiracy theory and common sense enough to be the big solution staring us in the face which nobody realized. Until now. Oak Ridge National Laboratory and General Electric (GE), working on a grant from the US Department of Energy (DOE), have been playing around with new clothes dryer technology since 2014 and have come with something new and exciting. Clothes dryers that use ultrasonic traducers to remove moisture from garments instead of using heat.

If you’ve ever seen a cool mist humidifier you’ll know how this works. A piezo element generates ultrasonic waves that atomize water and humidify the air. This is exactly the same except the water is stored in clothing, rather than a reservoir. Once it’s atomized it can be removed with traditional air movement.

This is a totally obvious application of the simple and inexpensive technology — when the garment is laying flat on a bed of transducers. This can be implemented in a press drying system where a garment is laid flat on a bed or transducers and another bed hinges down from above. Poof, your shirt is dry in a few seconds.

But individual households don’t have these kinds of dryers. They have what are called drum dryers that spin the clothes. Reading closely, this piece of the puzzle is still to come:

They play [sic] to scale-up the technoloogy to press drying and eventually a clothes dryer drum in the next five months.

We look at this as having a similar technological hurdle as wireless electricity. There must be an inverse-square law on the effect of the ultrasonic waves to atomize water as the water moves further away from the transducers. It that’s the case, tranducers on the circumference of a drum would be inefficient at drying the clothing toward the center. This slide deck hints that that problem is being addressed. It talks about only running the transducers when the fabric is physically coupled with the elements. It’s an interesting application and we hope that it could work in conjunction with traditional drying methods to boost energy savings, even if this doesn’t pan out as a total replacement.

With a vast population, cost adds up fast. There are roughly 125 M households in the United States and the overwhelming majority of them use clothes dryers (while many other parts of the world have a higher percentage who hang-dry their clothing). The DOE estimates $9 billion a year is spent on drying clothes in the US. Reducing that number by even 1/10th of 1% will pay off more than tenfold the $880,000 research budget that went into this. Of course, you have to outfit those households with new equipment which will take at least 8-12 years through natural attrition, even if ultrasonics hit the market as soon as possible.

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Gesture Recognition Using Ultrasound


You’d be hard pressed to find a public restroom that wasn’t packed full of hands free technology these days. From the toilets to the sinks and paper towel dispensers, hands free tech is everywhere in modern public restrooms.

The idea is to cut down on the spread of germs.  However, as we all know too well, this technology is not perfect. We’ve all gone from sink to sink in search of one that actually worked. Most of us have waved our hands wildly in the air to get a paper towel dispenser to dispense, creating new kung-fu moves in the process. IR simply has its limitations.

What if there was a better way? Check out [Ackerley] and [Lydia’s] work on gesture recognition using ultrasound. Such technology is cheap and could easily be implemented in countless applications where hands free control of our world is desired. Indeed, the free market has already been developing this technology for use in smart phones and tablets.

Where a video camera will use upwards of 1 watt of power to record video, an ultrasound device will use only micro watts. IR can still be used to detect gestures, as in this gesture based security lock, but lacks the resolution that can be obtained by ultrasound.  So let us delve deep into the details of [Ackerley] and [Lydia’s] ultrasound version of a gesture recognizer, so that we might understand just how it all works, and you too can implement your own ultrasound gesture recognition system.

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DIY Ultrasonic acoustic levitation

[Mike] saw a few videos of ultrasonic acoustic levitation rigs put together by student researchers. Figuring it couldn’t be that hard to replicate, he set out and built his own using surplus parts and whatever was sitting around his parts drawer.

The build began with a huge ultrasonic transducer from an old ultrasonic cleaning tank [Mike] picked up on eBay for $20 £20. He didn’t pick up the standard driver board, as those don’t have a very clean output – something desperately needed if you’re setting up a standing wave. He did manage to put a simple supply together with a 555 timer, a MOSFET and a 12 V transformer connected backwards, though.

The test rig is pretty simple – just the transducer sitting on a table with an aluminum plate sitting above it on threaded rods. By adjusting the distance between the transducer to the aluminum plate, [Mike] managed to set up some standing waves he was able to suspend small Styrofoam balls in. It’s not quite precise enough to levitate small chunks of sodium and water, but it makes for an excellent science fair-type project.

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