A 16-voice Homebrew Polyphonic Synth

Homebrew synths – generating a waveform in a microcontroller, adding a MIDI interface, and sending everything out to a speaker – are great projects that will teach you a ton about how much you can do with a tiny, low power uC. [Mark] created what is probably the most powerful homebrew synth we’ve seen, all while using a relatively low-power microcontroller.

The hardware for this project is an LPC1311 ARM Cortex M3 running at 72 MHz. Turning digital audio into something a speaker can understand is handled by a Wolfson WM8762, a stereo 24-bit DAC. Both of these chips can be bought for under one pound in quantity one, something you can’t say about the chips used in olde-tyme synths.

The front panel, shown below, uses 22 pots and two switches to control the waveform, ADSR, filter, volume, and pan. To save pins on the microcontroller, [Mark] used a few analog multiplexers. As far as circuitry goes, it’s a fairly simple setup, with the only truly weird component being the optocoupler for the MIDI input.

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The software for the synth is written mostly in assembly. In a previous version where most of the code was written in C, everything was a factor of two slower. Doing all the voice generation in assembly allowed for twice as many simultaneous voices.

It’s a great project, and compared to some of the other synth builds we’ve seen before, [Mark]’s project is at the top of its class. A quick search of the archives says this is probably the most polyphonic homebrew synth we’ve seen, and listening to the sound sample on the project page, it sounds pretty good, to boot.

Cloning a Board from Pictures on the Internet

[Andrew] was a pretty cool guy in the early 90s with an awesome keyboard synth that did wavetable synthesis, sampling, a sequencer, and an effects processor. This was a strange era for storage; a reasonable amount of Flash memory was unheard of, and floppy disks ruled the land. [Andrew]’s synth, though, had the option to connect SCSI drives. Like all optional add ons for high-end equipment, the current price for the Ensoniq SCSI card is astronomical and [Andrew] figured he could build one of these cards himself.

Poking around eBay, [Andrew] found the card in question – just a few passives, some connectors, a voltage regulator, and an odd chip from AMD. This chip was a 33C93A, a SCSI controller, and a trip down the Chinese vendor rabbit hole netted him one for $7. Can’t do better than that.

With the datasheet for the chip in hand and a few reasonable assumptions on how the circuit worked, [Andrew] tried to figure draw the schematic. After doing that, he found another hobbyist that had attempted the same project a few years earlier. All the nets were identical, and all that was left to do was sending a board off to the fab.

A quick trip to Front Panel Express got [Andrew] a mounting bracket for the card, and after plugging it in to the synth revealed a new option – SCSI. It worked, and with an ancient SCSI CD-ROM drive, he had boatloads of offline storage for his synth. Great work, and something we’d love to see more of.

 

Bluetooth Boombox for that 80s Nostalgia

Sure, anyone can go buy a bluetooth speaker for their portable music needs. But for something a little more unique, at least in this decade, [Daniel] aka [speedfox] went with an 80s-style boombox and outfitted it with a bluetooth module.

The retro boombox was delivered with a few scratches and a broken radio, but the tape decks were still in decent shape so it was ready to be hacked. [speedfox] tied the Bluetooth audio output to the tape reader on one of the boombox’s tape decks, but this revealed a problem: the bass was overwhelming the rest of the sound. [speedfox] fixed this by adding a filter which worked until the power was tied in to the Bluetooth module and produced a lot of RF noise in the audio output. THIS problem was finally resolved with an audio transformer on both sides of the stereo signal. Finally!

After putting all of the new electronics in the case (and safely out of the way of the 120V AC input!) [speedfox] now has a classy stereo that’s ready to rock some Run-D.M.C. or Heavy D. He notes that the audio filter could use a little tweaking, and he’d also like to restore the functionality of the original buttons on the boombox, but it’s a great start with more functionality than he’d get from something off-the-shelf!

Using MIDI and Magnets to Produce Tones with Tines

Normally you’d expect the sound of a pipe organ to come from something gigantic. [Matthew Steinke] managed to squeeze all of that rich melodic depth into an acoustic device the size of a toaster (YouTube link) which uses electromagnetism to create its familiar sound.

[Matthew ’s] instrument has a series of thin vertical tines, each coupled with a small MIDI controlled electromagnet. As the magnet pulses with modulation at a specific frequency, the pull and release of the tine causes it to resonate continuously with a particular tone. The Tine Organ is capable of producing 20 chromatic notes in full polyphony starting in middle C and can be used as an attachment to a standard keyboard or a synthesizer app on a smart phone. The classic style body of the instrument is made out of mahogany and babinga and houses the soundboard as well as the mini microcontroller responsible for receiving the MIDI and regulating the software oscillators sending voltage to the magnets.

[Matthew’s] creation is as interesting to look at as it is to listen to, so I’d recommend checking out the video below to hear the awesome sound it produces:

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Extreme Repair of a Burnt PCB

[xsdb] had a real problem. His JBL L8400P 600 watt subwoofer went up in flames – literally. Four of the large capacitors on the board had bulged and leaked. The electrolyte then caused a short in the mains AC section of the board, resulting in a flare up. Thankfully the flames were contained to the amplifier board. [xsdb’s] house, possessions, and subwoofer enclosure were all safe. The amplifier board however, had seen better days. Most of us would have cut our losses and bought a new setup. Not [xsdb] he took on the most extreme PCB repair we’ve seen in a long time.

After removing the offending caps and a few other components, [xsdb] got a good look at the damage. the PCB was burned through. Charred PCB is conductive, so anything black had to be cut out. The result was a rather large hole in the middle of an otherwise serviceable board. [xsdb] had the service manual for the JBL sub. Amazingly, the manual included a board layout with traces. Some careful Photoshop work resulted in an image of the section of PCB to be repaired. [Xsdb] used this image to etch a small patch board.

The amplifier and patch were milled and sanded to match up nearly perfectly. Incredibly, all the traces aligned. [Xdsb] soldered the traces across the join with small sections of wire and solder wick. After soldering in some new high quality capacitors, the amplifier was back in action!

If you’re a big fan of burned PCB’s, check out Hackaday Prize Judge Dave Jones latest EEVblog video, where he works on a Ness home alarm panel with a similarly cooked section of FR4.

[Thanks for the link JohnS_AZ!]

Make a Capacitive Clothespin Keyboard for Your iPad

Even with all the optimization and style of new technology, the keyboard is a difficult thing to replace. Touch screens just don’t deliver the tactile feedback that connects us to the medium. [Adam Kumpf] remedies this by building his own keyboard interface to work with an iPad piano app, all from craft materials you’d likely find lying around in the kitchen.

To make your own, you’d first need a bunch of clothespins which will ultimately act as your keys. [Adam] shows how to stitch the separated halves of the clothespins onto a piece of cardboard with some basic rubber bands. These tension the keys so that they can rock back and forth over a pen or pencil placed beneath them. When you press down on one end, the other lifts causing an opposing pin to press the corresponding key of the iPad, just like a hammer inside a piano. With a little aluminum foil for conductivity wrapped around the side making contact, you’ve got yourself a quick solution for your itch to rock some Chopin.

You can see how well the project works in action below in his video:

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Create a Buzz with the Mini Electric Ukulele

Everyone’s heard of the “World’s Smallest Violin,” but we think it’s time for something more upbeat. [Simone Giertz] of Punch Through Design has created a mini electric ukulele using a LightBlue Bean. The Bean is an Arduino-compatible microcontroller that you can wirelessly program using Bluetooth low energy (BLE).

The ukulele’s frame is made of laser-cut plywood.  Four 1M ohm resistors are soldered to individual wire strings. A different set of wire strings in the ukulele’s neck are connected to the same ground as the Bean. In order to play this tiny instrument, a finger must be kept on the “ground” strings while the other “tone” strings are touched by a different finger. [Simone] uses Arduino’s Capacitive Sensing Library to determine which string is being touched and what the tone will be (indicated in Hz). A piezo buzzer provides the sound. There is no need to fret when the battery is depleted from using this at an all-night luau: the frame can be unscrewed with easy access to the battery. [Simone] has uploaded the Bean’s code to GitHub.

There’s no shame going solo, but we’d enjoy a show of dueling mini-ukuleles. A duet with the 3D-printed ukulele is always a possibility. Or, play this little guy while running up and down some piano stairs while the kettle fife blows off some steam.  It’ll be a musical way to brighten anyone’s day. Check out the video of the mini ukelele after the break. You can also see more of [Simone’s] work at her website.

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