Smartphone Bench Instrument Apps: Disappointment or Delight?

If you are interested in electronics or engineering, you’ll have noticed a host of useful-sounding apps to help you in your design and build work. There are calculators, design aids, and somewhat intriguingly, apps that claim to offer an entire instrument on your phone. A few of them are produced to support external third-party USB instrument peripherals, but most of them claim to offer the functionality using just the hardware within the phone. Why buy an expensive oscilloscope, spectrum analyzer, or signal generator, when you can simply download one for free?

Those who celebrate Christmas somewhere with a British tradition are familiar with Christmas crackers and the oft-disappointing novelties they contain. Non-Brits are no doubt lost at this point… the crackers in question are a cardboard tube wrapped in shiny paper drawn tight over each end of it. The idea is that two people pull on the ends of the paper, and when it comes apart out drops a toy or novelty. It’s something like the prize in a Cracker Jack Box.

Engineering-oriented apps follow this cycle of hope and disappointment. But there are occasional exceptions. Let’s tour some of the good and the bad together, shall we?

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Characterizing A Cheap 500MHz Counter Module

An exciting development over the last few years has been the arrival of extremely cheap instrumentation modules easily bought online and usually shipped from China. Some of them have extremely impressive paper specifications for their price, and it was one of these that caught the eye of [Carol Milazzo, KP4MD]. A frequency counter for under $14 on your favourite online retailer, and with a claimed range of 500 MHz. That could be a useful instrument in its own right, and with a range that significantly exceeds the capabilities of much more expensive bench test equipment from not so long ago.

Just how good is it though, does it live up to the promise? [Carol] presents the measurements she took from the device, so you can see for yourselves. She took look at sensitivity, VSWR, and input impedance over a wide range, after first checking its calibration against a GPS-disciplined standard and making a fine adjustment with its on-board trimmer.

In sensitivity terms it’s a bit deaf, requiring 0.11 Vrms for a lock at 10 MHz. Meanwhile its input impedance decreases from 600 ohms at the bottom of its range to 80 ohms at 200 MHz, with a corresponding shift in VSWR. So it’s never going to match a high-end bench instrument from which you’d expect much more sensitivity and a more stable impedance, but for the price we’re sure that’s something you can all work around. Meanwhile it’s worth noting from the pictures she’s posted that the board has unpopulated space for an SPI interface header, which leaves the potential for it to be used as a logging instrument.

We think it’s worth having as much information as possible about components like this one, both in terms of knowing about new entrants to the market and in knowing their true performance. So if you were curious about those cheap frequency counter modules, now thanks to [Carol] you have some idea of what they can do.

While it’s convenient to buy a counter module like this one, of course there is nothing to stop you building your own. We’ve featured many over the years, this 100MHz one using a 74-series prescaler or this ATtiny offering for example, or how about this very accomplished one with an Android UI?

Musical Proximity Detection Pet Bowls

An essential skill for a maker is the ability to improvise or re-purpose existing materials into new parts. Sometimes, one needn’t make many modifications to create something new, as is the case with [Robin Sterling] and his musical pet bowl.

Originally, it was a sealed pet bowl that opened when the proximity sensors detected an approaching pet. Having helped design the bowl, [Sterling] had a bit of an advantage when he decided to convert it into a theremin/light harp-esque instrument for the company BBQ. He routed the PWM outputs from each of the three proximity sensors (in each of the three bowls) to a small guitar amp, adjusting each sensor’s output to a different frequency. Despite the short amount of time [Sterling] had to practice, it works fairly well!

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Super Massive Musical Instrument

Performing music in open spaces can be a real challenge. The acoustics of the space can play spoil-sport. Now imagine trying to play an instrument spread out over tens of kilometres. The folks at [LimbicMedia] wrote in to tell us about the project they worked on to build the The World’s Largest Musical Instrument.

The system consists of wirelessly controlled air horns deployed at remote locations. Each air horn is self contained, driven by a supply of compressed air from a scuba diving tank and battery powered electronics. The wireless link allows the air horns to be placed up to 10kms away from the base station. Each air horn is tuned to a specific note of the piano keyboard which, in turn, is configured to transmit its note data to the air horns.

HornsBeaconHill_02Currently, they have built 12 air horns, enough to let them play the Canadian and British anthems. The horns are built out of PVC piping and other off-the-shelf plastics with the dimensions of the horn determining its note. The setup was installed and performed at the Music by the Sea festival recently, by mounting the air horns on 12 boats which were stationed out at Sea in the Bamfield Inlet in Eastern Western Canada. But that was just a small trial. The eventual plan is to set up air horns all around Canada, and possibly other places around the world, and synchronise them to play music simultaneously, to commemorate the 150th Canada Day celebrations in 2017.

There aren’t many details shared about the hardware, but it’s not too difficult to make some guesses. A micro-controller to operate the air solenoid, long range radio link to connect all the air horns to the base station, and another controller to detect the key strokes on the Piano. The limiting issue to consider with this arrangement is the spatial separation between the individual air horns. Sound needs about 2.9 seconds to travel over a kilometer. As long as all the air horns are at approximately the same distance from the audience, this shouldn’t be a problem. See how they did in the video after the break. We do know of another project which handled that problem brilliantly, but we’ll leave the details for a future blog post.

This isn’t the first time [LimbicMedia] was commissioned to create audio-visual public installations. A couple of years back they built this Sound Reactive Christmas Tree in Victoria, British Columbia.

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Analog Clocks Play Their Own Beat

Play the demo video below and try not to let the rhythm worm its way into your brain. What you’re hearing is the sound of a bunch of clocks, amplified. None of them are keeping wall time, but all of them are playing together.

[Gijs] makes crazy musical instruments. He doesn’t give us much more than a video and a couple schematics for this project, so this one’s still a bit of an enigma, but here’s what we’ve put together.

Klok slave unit schematic
Klok slave unit schematic

The video looks like eight identical version of the same module. The input takes a voltage and converts the rising and falling edges into pulses to drive the coil of an el-cheapo clock. The LEDs pulse as the poles of the clock switch to the incoming beats. The output comes from an amplified piezo sensor stuck on the back of each clock. That is, what you’re hearing is each clock ticking, but amplified. And if you watch the dials spin, it doesn’t look like any of them are telling time.

So far so good, and it matches up with the schematic. But what’s up with that switch on the front? It doesn’t show up anywhere.

And what’s driving the show? [Gijs] tantalizes us with a master clock module (on the same page) that looks like it does keep time, and outputs subdivisions thereof. But that would be too slow to be what’s used in the video. Has he swapped the crystal to make it run faster? It’s a mystery.

Of course, we’d expect no less from the man who mics up a kitchen timer or a gear motor and adds them to his synthesizer rack. We’ve covered a bunch more of [Gijs]’s work in the past, from his video mixers to this hard-drive turned synth oscillator, but this time he’s got us scratching our heads a bit, as well as tapping our feet.

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Transmitting MIDI Signals With XBEE

What do you do when you want to rock out on your keytar without the constraints of cables and wires? You make your own wireless keytar of course! In order to get the job done, [kr1st0f] built a logic translator circuit. This allows him to transmit MIDI signals directly from a MIDI keyboard to a remote system using XBEE.

[kr1st0f] started with a MIDI keyboard that had the old style MIDI interface with a 5 pin DIN connector. Many new keyboards only have a USB interface, and that would have complicated things. The main circuit uses an optoisolator and a logic converter to get the job done. The MIDI signals are converted from the standard 5V logic to 3.3V in order to work with the XBEE.

The XBEE itself also needed to be configured in order for this circuit to work properly. MIDI signals operate at a rate of 31,250 bits per second. The XBEE, on the other hand, works by default at 9,600 bps. [kr1st0f] first had to reconfigure the XBEE to run at the MIDI bit rate. He did this by connecting to the XBEE over a Serial interface and using a series of AT commands. He also had to configure proper ID numbers into the XBEE modules. When all is said and done, his new transmitter circuit can transmit the MIDI signals wirelessly to a receiver circuit which is hooked up to a computer.

PVC Percussion Pipe Organ Sounds Surprisingly Good!

PVC Instrument

Using over 20′ feet of PVC pipe, a whole bunch of 2 x 4’s and a few nuts and bolts, [Jeremy] and his cousin put together a rather unique percussion pipe organ.

[Jackson], his cousin who is a musician is always looking for different ways to make music. They had a rough idea of what they wanted to do with a few sketches, but after a day of tinkering, they ended up with something completely different — but it sounds awesome.

The frame is made of a combination of 2 x 6’s and 2 x 4’s which hold the PVC tubes in place. PVC elbows and varying lengths of pipe create a wide range of rather deep bass notes. It can be played with just your hands, or even a pair of sandals for better effect. You’d be surprised how good it sounds.

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