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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Breadboarding with a ARM microcontroller

ARM

NXP’s LPC1114 ARM microcontroller is in a class all of it’s own. ARM microcontrollers are a dime a dozen, but this fabulous chip is the only one that’s housed in a hacker and breadboard friendly PDIP package. However, breadboard setups usually won’t have the luxuries of a true development platform such as flashing the part, single stepping through the code, and examining memory. [Steve] found an interesting solution to this problem that involves a Dremel and hacking up even more hardware.

[Steve] found a few LPC1769 dev boards that include a debugger and a way to program these chips. Simply by hacking off the programmer and debugger portion of this dev board with a Dremel tool, [Steve] had an easy to use interface for his breadboardable ARM.

After connecting the power rails to his breadboarded chip, [Steve] connected his programmer up and set up a gcc toolchain. For about $25, he has a breadboard friendly ARM microcontroller with full debugging capabilities.

This isn’t the first time we’ve seen a few people play with this DIP28 ARM chip; someone even milled this 600 mil chip down to 300 mils for even easier prototyping. Still, this is the best and cheapest way we’ve seen yet to turn this ARM into a proper prototyping platform.

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