Oscilloscope Piano Tuning 101

fft on scope

[Todd Harrison] recently wrote in to tip us off on his submission to the Tektronix oscilloscope contest – using a scope to tune a piano. In his video he demonstrates how a Fast Fourier Transform can be used to determine the fundamental frequency of the note being played. This is a quick and easy way to determine if that key is in tune, and if not, how far off it is from the desired frequency and in which direction.

He goes on to explain that a scope can only be used as a starting reference point since “mathematically correct” tuning on a piano doesn’t sound right to the human ear. It turns out that when struck, the stretched wires in the piano behave less than ideally. In the case of a piano, the overtones (the other peaks shown on the scope higher in frequency than the fundamental) are actually slightly sharper (higher in frequency) than the expected harmonic whole-number multiple of the fundamental frequency.  As a result, the frequency ranges of each octave must be “stretched” in order to accommodate this and sound correct when multiple notes are played together across octaves.

Typically, only the A4 key is actually tuned to its correct frequency of 440Hz and all of the other keys are manually tuned off of this baseline. The amount of necessary stretch applied to each octave increases as you get further away from this initial reference point in either direction and is unique to each and every individual instrument – thus there is no universal device capable of perfect tuning. Although [Todd] admits that he won’t attempt to tune the entire piano himself using this technique, he finds it a convenient way to keep the most heavily played center sections of the piano closer to true between professional tunings.

If you have any interesting or unique uses for your Techtronix scope, you can enter the contest here. Just don’t forget to tip us off too!  Thanks [Todd]!

Long-range laser night-vision

[Oneironaut] is back at it again, churning out yet another great hack in this long-distance night vision build. This isn’t the first time we’ve seen him build a night vision device, you may remember the monocle he put together using the view finder from an old camcorder. This time around he’ll give you look at distant object by using a laser instead of LEDs. He pulled an IR laser diode out of an old CD burner, then used a lens to spread out the dot in order to illuminate a larger area. A standard rifle scope is used as the optics, along with a security camera which can detect the infrared light. As always, he’s done a fantastic job with the images and the write-up. You’ll find his overview video embedded after the break.

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Waterproof DIY momentary-push switch

[Patman2700] has a nice scope for his paintball gun that uses a red dot instead of cross-hairs. The problem is that he kept forgetting to turn it off which ended up running the batteries down frequently. His solution to the problem was to get rid of the toggle switch used to turn it on and replace it will a home-made momentary push button switch. Now he presses the switch to aim and doesn’t waste juice when he’s running around, trying not to get pelted with paint.

Since this is used outside he wanted it to be water-tight. The switch is built using materials we’ve seen in previous diy switches; adhesive-backed copper sheets for conductors, foam to keep them separated until pressed, and plastic as a support. Copper is applied to the plastic base, with a ring of foam separating the base from the second layer of copper. When squeezed, the two layers of copper come in contact to complete the circuit. To make it work a bit better [Patman2700] added a dab of solder in the center of the bottom copper layer so there is less distance between conductors, and used extra foam to build up a bump in the center of the assembly for a better ‘button’ feel. The whole thing is encased in shrink-wrap with the seams sealed with super glue to keep moisture at bay.

Oscilloscope doubles as a serial terminal

PC-based USB oscilloscopes are fast becoming all the rage. [Matt Sarnoff’s] Terminalscope takes the reverse approach, adapting an oscilloscope into a full serial terminal. You may have seen something similar before in the Dutchtronix/SparkFun O-Clock, but [Matt’s] project goes one further by adding a PS/2 keyboard port for full bidirectional serial communication, and with much sharper display resolution to boot.

The mostly VT-100 compatible Terminalscope is built around two AVR microcontrollers: an ATmega328P runs full-tilt to generate the video signal and handle serial I/O, while an ATtiny45 handles keyboard input to avoid interrupting the ’328’s duties. Rather than vector trace each character, a raster-scanning approach is used: the beam follows a fixed X/Y path (like a television), while modulating the Z input (beam intensity) to form an image. The device can be connected to a PC via serial port or USB-to-TTY adapter, or directly to another microcontroller to debug serial output.

We recently showed an oscilloscope being used as a multichannel digital logic display. The Terminalscope provides yet another use for this essential bench tool and could nicely round out a “poor man’s” testing setup. The schematic and full source code are available for download.

Remote control pellet gun – with scope

Project Thunderbird is an automated predator and pest control system. It consists of a pellet gun mounted in a motorized base. The icing on the cake is a 60x zoom camera that has cross-hairs superimposed on the picture. This reminds us of the Internet hunting for the handicap we heard about years ago.

In the video after the break you can see how the motorized base works, watch the trigger-pull motor, and observe a demonstration of some target practice. The creator, [Gadgetapodimus], mentions the possible sale of plans and kits as soon as he completes the system. Perhaps it would be better if this was not easy for people to build.

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DSO nano oscilloscope reviewed

dsonano

We’ve been eyeing Seeed Studio’s DSO nano digital storage oscilloscope with a mix of intrigue and skepticism. A pocket-sized $89 storage ’scope? This is a joke, right? Hack a Day reader [Blair Thomson] has written a thorough review based on his experience with one of the beta test units, and it might be a winner after all.

[Blair] feels the unit compares favorably to buying a similarly-priced secondhand analog oscilloscope. The DSO nano wins major points for ease of use, a good range of functionality, and of course the whole portability thing (the enclosure is a repurposed portable media player). Can’t say we’re entirely convinced though. As a single-trace ’scope with 1 MHz bandwidth, the DSO nano may be extremely limiting for anything but basic hobbyist use…which, to be fair, is exactly how they’re marketing it. We can see a place for this the same way there’s a place for $10 multimeters — an inexpensive, toss-in-the-toolbag second ’scope to quickly test for vital signs, something that might complement but not replace a good bench unit.

Amazingly cheap dual channel scope

[Jacques] sent us this little project he has been working on. It is an amazingly cheap USB 2 chanel scope. The total cost of the project was around 5 Euros.  It is based off of an Atmel Tiny45, has 2 analog inputs, and can supply 5 Volts to a breadboard. He has listed the bill of materials as well as downloads for the source code, plans, and display software.