Year: 2017

How An Oscilloscope Probe Works, And Other Stories

March 15, 2017 by 29 Comments

The oscilloscope is probably the most versatile piece of test equipment you can have on your electronics bench, offering a multitude of possibilities for measuring timing, frequency and voltage as well as subtleties in your circuits revealed by the shape of the waveforms they produce.

On the front of a modern ‘scope is a BNC socket, into which you can feed your signal to be investigated. If however you simply hook up a co-axial BNC lead between source and ‘scope, you’ll immediately notice some problems. Your waveforms will be distorted. In the simplest terms your square waves will no longer be square.

Why is this? Crucial to the operation of an oscilloscope is a very high input impedance, to minimise current draw on the circuit it is investigating. Thus the first thing that you will find behind that BNC socket is a 1 megohm resistor to ground, or at least if not a physical resistor then other circuitry that presents its equivalent. This high resistance does its job of presenting a high impedance to the outside world, but comes with a penalty. Because of its high value, the effects of even a small external capacitance can be enough to create a surprisingly effective low or high pass filter, which in turn can distort the waveform you expect on the screen.

The answer to this problem is to be found in your oscilloscope probe. It might seem that the probe is simply a plug with a bit of wire to a rigid point with an earth clip, but in reality it contains a simple yet clever mitigation of the capacitance problem.

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Mechanical Music Maker Throws Stones

March 15, 2017 by 10 Comments

When we think of a xylophone we envision hitting the keys from above with mallets. But this robot instrument launches stones from below to play a tune. [Niel] calls the device a Pinger and it is part of a Rock Band — all instruments using rocks.

Although the original post has “xylophone” in it, this musical instrument is technically a glockenspiel because it uses metal keys instead of wood. Either way, it’s a work of art; the instrument’s creator ([Neil Mendoza]) was participating in Adobe’s Autodesk’s Pier 9 artist-in-residence program when he built it.

The keys were cut using a water jet, a process not easily in reach for most of us. But you could make do with a different process in a pinch. On the face of it, fabrication seems simple, but there’s software to calculate the right size for the keys depending on the material. The cuts need to be precise to yield an in-tune instrument.

The circular part is laser-cut acrylic, acting as a base for each key. Below the plate there is a cylinder positioned in the middle of the bar which keeps the stone from getting away. When the solenoid fires, the stone flies up and strikes the key, creating a ringing tone but also adding to the body of sound with a rattle when it falls back down to the base. The entire thing is driven by MIDI, so it can play a lot of tunes besides the biographical “Here Comes the Sun” (since, apparently, the pebbles are out in the sun). Check that out in the video below.

This couldn’t help but remind us of another solenoid-driven xylophone — whose keys were machined out of aluminum stock. There’s also the multixylophoniomnibus.

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This WAV File Can Confuse Your Fitbit

March 15, 2017 by 30 Comments

As the devices with which we surround ourselves become ever more connected to the rest of the world, a lot more thought is being given to their security with respect to the internet. It’s important to remember though that this is not the only possible attack vector through which they could be compromised. All devices that incorporate sensors or indicators have the potential to be exploited in some way, whether that is as simple as sniffing the data stream expressed through a flashing LED, or a more complex attack.

Researchers at the University of Michigan and the University of South Carolina have demonstrated a successful attack against MEMS accelerometers such as you might find in a smartphone. They are using carefully crafted sound waves, and can replicate at will any output the device should be capable of returning.

MEMS accelerometers have a microscopic sprung weight with protruding plates that form part of a set of capacitors. The displacement of the weight due to acceleration is measured by looking at the difference between the capacitance on either side of the plates.

The team describe their work in the video we’ve put below the break, though frustratingly they don’t go into quite enough detail other than mentioning anti-aliasing. We suspect that they vibrate the weight such that it matches the sampling frequency of the sensor, and constantly registers a reading at a point on its travel they can dial in through the phase of their applied sound. They demonstrate interference with a model car controlled by a smartphone, and spurious steps added to a Fitbit. The whole thing is enough for the New York Times to worry about hacking a phone with sound waves, which is rather a predictable overreaction that is not shared by the researchers themselves.

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Storing Data On A Single Atom

March 14, 2017 by 11 Comments

In the electronics industry, the march of time brings with it a reduction in size. Our electronic devices, while getting faster, better and cheaper, also tend to get smaller. One of the main reasons for this is the storage medium for binary data gets smaller and more efficient. Many can recall the EPROM, which is about the size of your thumb. Today we walk around with SD cards that can hold an order of magnitude more data, which can fit on your thumb’s nail.

Naturally, we must ask ourselves where the limit lies. Just how small can memory storage get? How about a single atom! IBM along with a handful international scientists have managed to store two bits of information on two pairs of holmium atoms. Using a scanning tunneling microscope, they were able to write data to the atoms, which held the data for an extended period of time.

Holmium is a large atom, weighing in at a whopping 67 AMU. It’s a rare earth metal from the lanthanide series on the periodic table. Its electron configuration is such that many of the orbiting electrons are not paired. Recall from our article on the periodic table that paired electrons must have opposite spin, which has the unfortunate consequence of causing the individual magnetic fields to cancel. The fact that holmium has so many unpaired electrons makes it ideal for manipulation.

While you won’t be seeing atom-level memory on the next Raspberry Pi, it’s still neat to see what the future holds.

Thanks to [Itay] for the tip!

Via Gizmodo.

Google Machine Learning Made Simple(r)

March 14, 2017 by 18 Comments

If you’ve looked at machine learning, you may have noticed that a lot of the examples are interesting but hard to follow. That’s why [Jostmey] created Naked Tensor, a bare-minimum example of using TensorFlow. The example is simple, just doing some straight line fits on some data points. One example shows how it is done in series, one in parallel, and another for an 8-million point dataset. All the code is in Python.

If you haven’t run into it yet, TensorFlow is an open source library from Google. To quote from its website:

TensorFlow is an open source software library for numerical computation using data flow graphs. Nodes in the graph represent mathematical operations, while the graph edges represent the multidimensional data arrays (tensors) communicated between them. The flexible architecture allows you to deploy computation to one or more CPUs or GPUs in a desktop, server, or mobile device with a single API. TensorFlow was originally developed by researchers and engineers working on the Google Brain Team within Google’s Machine Intelligence research organization for the purposes of conducting machine learning and deep neural networks research, but the system is general enough to be applicable in a wide variety of other domains as well.

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Hush Those Old-Fashioned Phones

March 14, 2017 by 26 Comments

Most people hate unsolicited calls, and it’s worse in the dead of night when we’re all trying to sleep. Smartphones are easy to configure to block nuisance calls, but what if you need a solution for your Plain Old Telephone System (POTS)? [Molecular Descriptor] has built a system to invisibly stop landline phones ringing after hours.

The basic principle relies on an analog circuit that detects the AC ringing signal from the phone network, and then switches in an impedance to make the phone company think the phone has been picked up. The circuit is able to operate solely on the voltage from the phone line itself, thanks to the use of the LM2936 – a regulator with an ultra-low quiescent current. It’s important if you’re going to place a load on the phone line that it be as miniscule as possible, otherwise you’ll have phone company technicians snooping around your house in short order wondering what’s going on.

The aforementioned circuitry is just to block the phone line. To enable the system to only work at night, more sophistication was needed. An Arduino Mega was used to program an advanced RTC with two alarm outputs, and then disconnected. The RTC is then connected to a flip-flop which connects the blocking circuit only during the requisite “quiet” hours programmed by the Arduino. The RTC / flip-flop combination is an elegant way of allowing the circuit to remain solely powered by the phone line in use, as they use far less power when properly configured than a full-blown microcontroller.

It’s a cool project, with perhaps the only pitfall being that telecommunications companies aren’t always cool with hackers attaching their latest homebrewed creations to the network. Your mileage may vary. For more old-school telephony goodness, check out this home PBX rig.

Arpeggio – The Piano SuperDroid

March 14, 2017 by 43 Comments

I never had the musical talent in me. Every now and then I would try to pick up a guitar or try and learn the piano, romanticising a glamorous career out of it at some point. Arpeggio – the Piano SuperDroid (YouTube, embedded below) sure makes me glad I chose a different career path. This remarkable machine is the brain child of [Nick Morris], who spent two years building it.

Although there are no detailed technical descriptions yet, at its heart this handsome robot consists of a set of machined ‘fingers’ connected to a set of actuators — most likely solenoids . The solenoids are controlled by proprietary software that combines traditional musical data with additional parameters to accurately mimic performances by your favourite pianists, right in your living room. Professional pianists, who were otherwise assuming excellent job security under Skynet, clearly have to reconsider now.

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