Raspberry Pi Pico Becomes MIDI-Compatible Synth

ECE 4760 is a microcontroller course that runs at Cornell every year, and it gives students a wide remit to pursue various kinds of microcontroller projects. [Pelham Bergesen] took the class and built himself a MIDI-controllable synthesizer out of a Raspberry Pi Pico.

[Pelham] coded a library to parse MIDI messages on the Pico, with the microcontroller’s UART charged with receiving the input data. MIDI is basically just serial at a baud rate of 31.25k, with a set message structure, after all. From there, the Pico takes the note data and plays the relevant frequencies by synthesizing square waves using a PWM output. A second PWM channel can also be blended with the first to generate more complex tones.  The synthesizer is designed to be used with a source of MIDI note data such as a keyboard controller; [Pelham] demonstrates the project in use with a Roland JD-XI. It’s a fairly basic synthesizer, but [Pelham] does a good job of explaining all the steps required to get this far. If you’ve never done an audio or MIDI project before, you might find his guide very helpful for the way it steps through the basics.

[Pelham] didn’t get to implement fancier features like direct digital synthesis (DDS) or analog audio effects before the class closed out. However, that would be an excellent project for anyone else developing their own Pico synthesizer. If you whip up something that sounds good, or even just interesting, be sure to notify us on the tipsline. Video after the break.

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The Reverse Oscilloscope

Usually, an oscilloscope lets you visualize what a signal looks like. [Mitxela]’s reverse oscilloscope lets you set what you want an audio waveform to look like, and it will produce it. You can see the box in the video below.

According to [Mitxela] part of the difficulty in building something like this is making the controls manageable for mere mortals. We really like the slider approach, which seems pretty obvious, but some other controls are a bit more subtle. For example, the interpolation control can create a squarish wave or a smooth waveform, or anything in between.

This is sort of an artistic take on an arbitrary waveform generator but with a discrete-panel user interface. The device contains a Teensy, a Raspberry PI Pico, a 16-bit ADC, and an external DAC. The Pico is little more than an I/O controller, reading the user interface and transmitting it on a serial port.

The outside construction looks excellent (we assume the tape is temporary). The inside is a bit messier, but still nicely done. There are many photos of the construction and details of problems along the way with 12-bit ADCs and power supply experiments.

Of course, if you don’t need the user interface, you can go crazy with waveform generation. We did our own similar project, but you could draw your waveforms on the PC instead of sliders.

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Mangle Videos With RecurBOY And A Raspberry Pi Zero

You used to need a lot of equipment to be a video DJ. Now you can do it all with a Raspberry Pi Zero and [cyberboy666]’s recurBOY. And if you missed out on the 1970’s video-editing psychedelia, now’s your chance to catch up – recurBOY is a modern video synth with all of the bells and whistles, and it’ll fit in your pocket. Check out [cyberboy666]’s demo video if you don’t yet know what you’re getting into. (Embedded below.)

RecurBOY has four modes: video, shader, effects, and external input, and each of these is significantly cooler than the previous. Video mode plays videos straight off of the SD card through the recurBOY’s composite video out. Shader mode lets you program your own shaders using the GLES shader dialect for resource-constrained devices. And this is where the various knobs and buttons come in. You can program the various shader routines to read any of the pots as input, allowing you to tweak the graphics demos on the fly.

Effects mode overlays your shaders on the video that’s playing, and external mode allows you to plug in a USB video capture card or a webcam so you can do all that same mangling with a live camera feed. And these two modes are where it gets awesome. The shader effects in the demo video cover all of the analog classics – including bloom and RGB separation – but also some distinctly digital effects. And again, you can tweak them all live with the knobs. Or plug in a MIDI controller and control it all externally. What hasn’t he thought of?

Old school analog video effects are really fun, and recurBOY brings them to you with the flexibility of modern shader coding. What’s not to love? If you want to see the pinnacle of the pre-digital era, that would be the Scanimate. For a video synth that integrates with your audio synth, check out Hypno. And if glitching the video is more your style, you can hijack the RAM of a VGA/composite converter.

Trippy, man!

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Compose Any Song With Twelve Buttons

Limitations placed on any creative process often paradoxically create an environment in which creativity flourishes. A simple overview of modern pop, rock, or country music illustrates this principle quite readily. A bulk of these songs are built around a very small subset of music theory, often varying no more than the key or the lyrics. Somehow, almost all modern popular music exists within this tiny realm. [DeckerEgo] may have had this idea in mind when he created this tiny MIDI device which allows the creation of complex musical scores using a keyboard with only 12 buttons.

The instrument is based around the Adafruit MacroPad, which is itself built on the RP2040 chip. As a MIDI device, it needs to be connected to a computer running software which can support MIDI instruments, but once its assembled and given its firmware, it’s ready to rock. A musician can select one of any number of musical scales to operate within, and the 12 keys on the pad are mapped to the 12 chromatic notes within that scale. It can also be used to generate drum tracks or other backing tracks to loop before being used to create melodies as well.

[DeckerEgo] took a bit of inspiration from an even simpler macro pad we featured before which is based around the idea that a shockingly high number of songs use the same four chords. His macro pad includes creation of chord progressions as well, but expands on that idea to make more complete compositions possible. And, for those looking to build their own or expand on this project, he has also made all of the source code available on his GitHub page.

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Mechanical Keyboard As Travel Saxophone

Those who play larger musical instruments, things like drums, piano, harp, tuba, upright bass, or Zeusaphone, know well the challenges of simply transporting their chosen instrument to band practice, a symphony hall, or local watering hole. Even those playing more manageably-sized instruments may have similar troubles at some point especially when traveling where luggage space is at a premium like on an airplane. That’s why [jcard0na] built this electronic saxophone, designed to be as small as possible.

Known as the “haxophone”, the musical instrument eschews the vibrating column of air typical of woodwind instruments in favor of an electronic substitute. Based around the Raspberry Pi, the device consists of a custom HAT with a number of mechanical keyboard switches arrayed in a way close enough to the layout of a standard saxophone that saxophonists will be able to intuitively and easily play. Two pieces of software run on the Pi to replicate the musical instrument, one that detects the player’s breaths and key presses, and another that synthesizes this information into sound.

While [jcard0na] notes that this will never replicate the depth and feel of a real instrument, it does accomplish its design goal of being much more easily transportable than all but the most soprano of true saxophones. As a musical project it’s an excellent example of good design as well, much like this set of electronic drums with a similar design goal of portability.

A man sits in front of a wooden table. There is a black box with a number of knobs hand-labeled on blue painter's tape. A white breadboard with a number of wires protruding from it is visible on the box's left side. An oscilliscope is behind the black box and has a yellow waveform displaying on its screen.

A More Expressive Synth Via Flexure

Synthesizers can make some great music, but sometimes they feel a bit robotic in comparison to their analog counterparts. [Sound Werkshop] built a “minimum viable” expressive synth to overcome this challenge. (YouTube)

Dubbed “The Wiggler,” [Sound Werkshop]’s expressive synth centers on the idea of using a flexure as a means to control vibrato and volume. Side-to-side and vertical movement of the flexure is detected with a pair of linear hall effect sensors that feed into the Daisy Seed microcontroller to modify the patch.

The build itself is a large 3D printed base with room for the flexure and a couple of breadboards for prototyping the circuits. The keys are capacitive touch pads, and everything is currently held in place with hot glue. [Sound Werkshop] goes into detail in the video (below the break) on what the various knobs and switches do with an emphasis on how it was designed for ease of use.

If you want to learn more about flexures, be sure to checkout this Open Source Flexure Construction Kit.

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Arduino Synthesizer Uses Modified Slide Pots

There comes a point in every Arduino’s life where, if it’s lucky, it becomes a permanent fixture in a project. We can’t think of too many better forever homes for an Arduino than inside of a 3D-printed synthesizer such as this 17-key number by [ignargomez] et al.

While there are myriad ways to synthesizer, this one uses the tried-and-true method of FM synthesis courtesy of an Arduino Nano R3. In addition to the 17 keys, there are eight potentiometers here — four are used for FM synthesis control, and the other four are dedicated to attack/delay/sustain/release (ADSR) control of the sound envelope.

One of the interesting things here is that [ignargomez] and their team were short a few regular pots and modified a couple of slide pots for circular use — we wish there was more information on that. As a result, the 3D printed enclosure underwent several iterations. Be sure to check out the brief demo after the break.

Don’t have any spare Arduinos? The BBC Micro:bit likes to make noise, too.

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