Anyone Need a Little Fuming Nitric Acid?

If there’s a chemical with a cooler name than “fuming nitric acid,” we can’t think of it. Nearly pure nitric acid is useful stuff, especially if you’re in the business of making rocket fuels and explosives. But the low-end nitric acid commonly available tops out at about 68% pure, so if you want the good stuff, you’ll have to synthesize fuming nitric acid yourself. (And by “good stuff”, we mean be very careful with the resulting product.)

Fuming nitric acid comes in two colors – red fuming nitric acid (RFNA), which is about 90% pure and has some dissolved nitrogen oxides, giving it its reddish-brown color. White fuming nitric acid (WFNA) is the good stuff — more than 99% pure. Either one is rough stuff to work with — you don’t want to wear latex or nitrile gloves while using it. It’s not clear what [BarsMonster] needs the WFNA for, although he does mention etching some ICs. The synthesis is pretty straightforward, if a bit dangerous. An excess of sulfuric acid is added to potassium nitrate, and more or less pure nitric acid is distilled away from the resulting potassium sulfate. Careful temperature control is important, and [BarsMonster] seems to have gotten a good yield despite running out of ice.

We don’t feature too many straight chemistry hacks around here, but this one seemed gnarly enough to be interesting. We did have a Hackaday Prize entry a while back on improvements to the Haber process for producing ammonia, which curiously is the feedstock for commercial nitric acid production processes.

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Piana – Musical Synthesis For The Raspberry Pi

For the last 15 years or so, software synths have slowly yet surely replaced those beatboxes, drum machines, and true synthesizers. It’s a loss for old hardware aficionados, but at least everyone with a MacBook is now a musician, amiright?

The Raspberry Pi and Pi2 already have more processing power than a desktop from ’99, so it’s no surprise that all of those classic synths, from a Moog. Yamaha DX, Casio CZ, Linn drum machine, Fairlight, and a mellotron, can all be stuffed into a Pi thanks to the work of [Phil Atkin] and his Raspberry Pi synthesizer.

[Phil]’s efforts to bring audio synthesis to the Pi fall under three techniques: subtractive synthesis, phase distortion synthesis, and sample-based synthesis, something that’s found in everything from Akai MPCs, MacBooks, and that one episode of The Cosby Show. [Phil] is combining all of these techniques into a piece of software that’s capable of running seamlessly on the Pi, giving anyone with a $35 computer a tool that would have been worth several thousand dollars in 1985.

The project is pretty far along, but the recent release of the Raspberry Pi 2 has thrown [Phil] for a loop. On one hand, the Pi 2 is much more capable than the original Pi in terms of hardware, and this lends itself to more sounds and a better GUI. On the other hand, there are millions of original Pi 1s out there that still make for exceptional synthesizers. Either way, [Phil]’s work is a great example of how far you can push the Pi with audio work.

Thanks [Wybren] for the tip. Videos below.

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Two saxophone synthesizer builds for the price of one

[Bruce Land] has been sending in student projects from the electronic design course he taught at Cornell last semester. By a curious coincidence, two groups build saxophone synthesizers with the same key arrangement as a real sax.

First up is [Brian Wang]’s digital sax. There’s a small microphone in the mouthpiece and a series of buttons down the body of the sax telling the ATMega664 what note to play. The data for the saxophone synthesis was created by looking at a frequency plot of a sax, bassoon, harp, and pipe organ. [Brian] has the synthesis part down pat; there’s definitely a baritone sax in that little microcontroller.

Next up is [Suryansh] and [Chris]’s PVC pipe saxophone. It’s the same general principle as [Brian]’s project – the musician blows into the sax (we really like the kazoo mouthpiece) and a small mic picks up the sound of the wind. If the microphone output is above a certain threshold, the buttons are read and a note come out of the sax. We’re picking up a whiff of alto sax here; shame there wasn’t a duet with the two teams.

After the break you can see both saxophone projects in all their glory.

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