Making An ARM Powered MIDI Synthesizer

What you see in the picture above is a hand-made 4-oscillator synthesizer with MIDI input, multi-mode filter and a handful of modulation options. It was built by [Matt], an AVR accustomed electronics enthusiast who made an exception to his habits for this project. The core of the platform is a DIP packaged 32-bit Cortex-M0 ARM processor (LPC1114), stuffed with ‘hand’ written assembly code and compiled C functions. With a 50MHz clock speed, the microcontroller can output samples at 250kHz on the 12bit DAC while being powered by 3 AA batteries.

Reading [Matt]‘s write-up, we discover that the firmware he created uses 4 oscillators (sawtooth or pulse shape) together with a low frequency oscillator (triangle, ramp, square, random shapes). It also includes a 2-pole state-variable filter and the ability to adjust the attack-release envelopes (among others). The system takes MIDI commands from a connected device. We embedded videos of his creation in action after the break.

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Meet the Teensy 3.1

[Paul Stoffregen] just released an updated version of his Teensy 3.0, meet the oddly named Teensy 3.1. For our readers that don’t recall, the Teensy 3.0 is a 32 bit ARM Cortex-M4 based development platform supported by the Arduino IDE (using the Teensyduino add-on). The newest version has the same size, shape & pinout, is compatible with code written for the Teensy 3.0 and provides several new features as well.

The Flash has doubled, the RAM has quadrupled (from 16K to 64K) allowing much more advanced applications. The Cortex-M4 core frequency is 72MHz (48MHz on the Teensy 3.0) and the digital inputs are 5V volts compatible. Pins 3 and 4 gained CAN bus functions. The new microcontroller used even has a 12 bits Digital to Analog Converter (DAC) so you could create a simple signal generator like the one shown in the picture above. Programming is done through the USB port, which can later behave as host or slave once your application is launched. Finally, the price tag ($19.80) is in our opinion very reasonable.

Embedded below is an interview with its creator [Paul Stroffregen].

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Speeding Up BeagleBone Black GPIO A Thousand Times

scope

For both the Raspberry Pi and BeagleBone Black, there’s a lot of GPIO access that happens the way normal Unix systems do – by moving files around. Yes, for most applications you really don’t need incredibly fast GPIO, but for the one time in a thousand you do, poking around /sysfs just won’t do.

[Chirag] was playing around with a BeagleBone and a quadrature encoder and found the usual methods of poking and prodding pins just wasn’t working. By connecting his scope to a pin that was toggled on and off with /sysfs he found – to his horror – the maximum speed of the BBB’s GPIO was around three and a half kilohertz. Something had to be done.

After finding an old Stack Overflow question, [Chirag] hit upon the solution of using /dev/mem to toggle his pins. A quick check with the scope revealed he was now toggling pins at 2.8 Megahertz, or just about a thousand times faster than before.

Breadboard Friendly ARM Board Based on STM32F4

breadboard-friendly-stm32-dev-board

Umm yeah… this is more like it. The STM32F4Stamp is a project which [Frank Zhao] put together to make his ARM prototyping process more like is was back when everything came in a DIP format. As you can see, it’s just narrow enough to leave one row open on the breadboard for jumper wires.

Don’t get us wrong, we do really like STM’s own Discovery Boards for the hardware they deliver at a very low price. But the dual-row pin headers on the larger versions (all except the F0 variant) make it tricky to connect your peripherals. This is pushed to the point that a large percentage of hacks we’ve seen with the Discovery boards are actually just to make connecting external hardware easier.

You may be thinking that there’s a lot missing from this board, but we disagree. Obviously there’s still a USB port which can be used to power the board via a 3.3V regulator. But since the STM32 chips have a built-in bootloader the USB connection can also be used to flash firmware to the processor. Nice! It’s open hardware if you want roll your own. For your convenience we’ve embedded the schematic after the break, along with [Frank's] demo video.

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Interview with [Damien George], Creator of the Micro Python project

upython

[Damien George] just created Micro Python (Kickstarter alert!), a lean and fast implementation of the Python scripting language that is optimized to run on a microcontroller. It includes a complete parser, compiler, virtual machine, runtime system, garbage collector and was written from scratch. Micro Python currently supports 32-bit ARM processors like the STM32F405 (168MHz Cortex-M4, 1MB flash, 192KB ram) shown in the picture above and will be open source once the already successful campaign finishes. Running your python program is as simple as copying your file to the platform (detected as a mass storage device) and rebooting it. The official micro python board includes a micro SD card slot, 4 LEDs, a switch, a real-time clock, an accelerometer and has plenty of I/O pins to interface many peripherals. A nice video can be found on the campaign page and an interview with the project creator is embedded after the break.

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Windows CE On A Raspberry Pi

WinCE

From all the BSDs and Linuxes to extraordinarily odd operating systems, it seems just about every OS has been ported to the Raspberry Pi. All except Windows, that is, but a few people are working on it.

This build comes to us from [ideeman] who wanted to show off his Raspi running Windows Compact Embedded. It technically works, but there are still a few problems. In his own words:

Unfortunately, as it is now, I can’t really control it through anything else than via the kernel transport layer (through serial, directly to visual studio, and I still get lots of checksum errors, must me from the cheapo USB<==>TTL 3.3V adapter I’m using). The original developer (dboling) is still struggling with native USB drivers, but as you can see, he already got a (unaccelerated) running display driver.

If you’re interested, I can send you the compiled kernel image, but I don’t think you’ll do really much without the serial debugging provided through Visual Studio 2008 (+Platform builder 7.0)… I’m not sure it can be legally released to the public though.

While running Windows Compact Embedded isn’t as cool as running Windows RT on a Raspi, the latter will never happen. Windows RT requires 1 GB of RAM and a 1 GHz ARM v7 processor, neither of which the Pi has. Still, it’s a very impressive hack and with a few more devs on board, [dboling] and [ideeman] might end up with a truly functional system.

Below are pics of [ideeman]‘s Raspi running WinCE. For [ideeman], feel free to link to a torrent in the comments.

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An ARM Powered Business Card, Part Two

Card

While most microcontroller powered business cards opt for something small and cheap, [Brian] is going in an entirely different direction. His business card features an ARM processor, some Flash storage, a USB connection, and enough peripherals to do some really cool stuff.

This is the second iteration of [Brian]‘s business card. We saw the first version, but this new version makes up for a few mistakes in the previous version. The biggest improvement is the replacement of the Molex USB plug with bare traces on the board. [Brian] couldn’t find a board house that could fab a board with the proper thickness for a USB plug, but a few strips of masking tape did enough to beef up the thickness and make his plug nice and snug. Also, the earlier version had a few pins sticking out of the board for programming purposes. This wasn’t an idea solution for a business card where it would be carried around in a pocket, so these pins were replaced with a connectorless programming adapter. Just a few exposed pads gives [Brian] all the programming abilities of the last version, without all those prickly pins to catch on clothing.

With his new business card, [Brian] has an excellent display of his engineering prowess and a very cool toy; he has a project that will turn this card into a keyboard emulator, randomly activating the Caps Lock button for a few seconds every few minutes. A great prank, and a great board to give to future employers.

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