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.


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.

Running Debian on a Graphing Calculator

While the ubiquitous TI-83 still runs off an ancient Zilog Z80 processor, the newer TI-Nspire series of graphing calculators uses modern ARM devices. [Codinghobbit] managed to get Debian Linux running on a TI-Nspire calculator, and has written a guide explaining how it’s done.

The process uses Ndless, a jailbreak which allows code to run at a low level on the device. Ndless also includes a full SDK, emulator, and debugger for developing apps. In this case, Ndless is used to load the Linux kernel.

The root filesystem is built on a PC using debootstrap and the QEMU ARM emulator. This allows you to install whatever packages are needed via apt, before transitioning to the calculator itself.

With the root filesystem on a USB flash drive, Ndless runs the Linux loader, which starts the kernel, mounts the root filesystem, and boots in to a Debian system in about two minutes. As the video after the break demonstrates, this leaves you with a shell on the calculator. We’re not exactly sure what to do with Linux on a graphing calculator, but it is a neat demonstration.

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Hackaday Links: November 16, 2014

There have been a few people asking us to do our full teardown of a crowdfunding campaign, this time for Bleen. We’ll get to that, but here’s the TL;DR version: 208 people just threw money away, and right now Indiegogo is ~$3000 richer for doing nothing.

Insipired by a Hacklet, [Chris] documented his retro console build. He started out like most people do with a Raspberry Pi, but found emulating newer consoles like the N64 consumed too much processor time. He moved his build over to custom-assembled hardware with an AMD Micro-ATX board, a drive, and a USB gamepad. It’s beautiful, and much, much more powerful than a Raspberry Pi.

SD card in your Pi died? Of course it did. The problem is you’re not shutting down your Pi correctly. [satya] whipped up a quick project to fix that. One button, a bit of Python, and a shell script is all you need for a one-button shutdown for your Raspberry Pi.

A while ago, [Jan] built an ARM-based modeling MIDI synth that sounds a lot like the old Junos of the 80s. It’s build around the one 8-pin DIP ARM that’s being manufactured, placed between a MIDI jack and a 1/4″ jack. That’s pretty much all the components. [Gritty] plugged it into a Teensy that’s connected to a sequencer. It sounds awesome.

Everyone loves the Spark Core – there are a few floating around the office here. Now there’s a new Spark. It’s called the Photon, and they’re packaging it as a module. There’s an STM32F2 microcontroller and a BCM43362 Wi-Fi transceiver packaged in a nice, FCC certified module. Very cool.

This Home-Made 6-Axis Robotic Arm is Quite the Looker

With a background in software engineering, [Kris Temmerman] decided to make a physical demonstration of his knowledge in the form of a six axis robotic arm… the final product is a delicious display of mechanical eye candy.

Built from mostly aluminum stock, [Kris] machined the bulk of his parts with a CNC mill which he picked up for cheap from China. These custom pieces coupled with some hefty stepper motors ensure the arm’s accuracy as it twists freely and slides along the gantry it’s mounted to. Though the majority of the arm is metal, the hand at the end of his robot was built with 3D printed parts and can be switched out with the future attachments [Kris] plans to design. This classic gripper piece is driven separately with its own Arduino brain controlling the individual servos in the fingers. loadcels

Each finger includes some load bearing sensors which [Kris] harvested from an old scale so that the gripper can tell whether or not it has a hold of an object without crushing it. To orchestrate the robot’s movement, he wrote some nice looking software in C++ which visualizes the inverse kinematics at work in each point of articulation. For the sake of demonstrating his creation in action, he whipped up a basic demo that can locate and move colored blocks laid at random on a surface. A small camera mounted on the hand determines the orientation of the blocks relative to the machine so that the wrist can rotate itself in the proper alignment in order to pick them up.

[Kris] documented the build of his robot in a fascinating speed video which includes footage of the finished arm in action at the end:

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Here’s something that’s just a design study, but [Ivan]’s Apple IIe phone is a work of art. You’re not fitting a CRT in there, but someone out there has a 3D printer, an old LCD, and a GSM module. Make it happen. See also: the Frog Design Apple phone.

A few days ago we posted something on an old ‘286 machine that was able to load up the Hackaday retro site. For a few people, this was the first they’ve heard about our CSS and Javascript-less edition designed specifically for old computers. They dragged out some hardware, and [WTH] pulled up the site on a Dell Axim.It’s actually somewhat impressive that these machines have SD cards…

[Arduino Enigma] created a touchscreen Enigma machine. Why haven’t we seen an Arduino Colossus yet?

The crew at Adafruit now have a Flying Toaster OLED, which means we now have flying toaster bitmaps for all your OLED/graphic display projects.

[Ian] had an old rackmount programmable voltage standard. This was the remote programmable voltage standard, without front panel controls. No problem, just get an Arduino, shift register, and a few buttons. Video right here.

A few months ago, [Jan] released a neat device that stuffs a modelling synth inside a MIDI plug. He’s selling them now, and we’d love to see a few videos of this.

Game Tin: Handheld Games with no Batteries

Anyone who grew up with a Game Boy knows how well they sucked through AA batteries. [Nick]’s Game Tin console solves this problem by running of an ultracapacitor charged by solar power.

The console is based on a EFM32 microcontroller: an ARM device designed for low power applications. The 128×128 pixel monochrome memory display provides low-fi graphics while maintaining low power consumption.

There’s two solar cells and a BQ25570 energy harvesting IC to charge the ultracap. This chip takes care of maximum power point tracking to get the most out of the solar cells. If it’s dark out, the device can be charged in about 30 seconds by connecting USB power.

The 10 F Maxwell ultracapacitor can run a game on the device for 1.5 hours without sunlight, and the device runs indefinitely in the sun. Thanks to the memory display, applications that have lower refresh rates will have much lower power consumption.

The Game Tin is open source, and is being developed using KiCad. You can grab all the EDA files from Bitbucket. [Nick] is also gauging interest in the Game Tin, and hopes to release it as a kit.

Introducing USB Armory, a Flash Drive Sized Computer

[Andrea] tipped us about USB armory, a tiny embedded platform meant for security projects. It is based on the 800MHz ARM Cortex-A8 Freescale i.MX53 together with 512MB of DDR3 SDRAM, includes a microSD card slot, a 5-pin breakout header with GPIOs/UART, a customizable LED and is powered through USB.

This particular processor supports a few advanced security features such as secure boot and ARM TrustZone. The secure boot feature allow users to fuse verification keys that ensure only trusted firmware can be executed on the board, while the ARM TrustZone enforces domain separation between a “secure” and a “normal” world down to a memory and peripheral level. This enables many projects such as electronic wallets, authentication tokens and password managers.

The complete design is open hardware and all its files may be downloaded from the official GitHub repository. The target price for the final design of the first revision is around €100.