plexus

hardware

A prototype version of the plexus hardware has been built in order to test and refine the concept. The prototype was built on perfboard and housed in a guitar pedal enclosure. Future work will include a pcb and panel layout according to the eurorack modular standard.

The hardware consists of a usb midi host, a teensy 3.2 microcontroller, 4 channels of 12 bit DAC, 5 transistor driven gate outputs and 1 gate input.

I will put a proper schematic here when I have drawn it.

power

A 7805 regulator is used to supply 5v to the device. In the prototype this is fed from a standard 9v guitar plug pack. It should be possible to power this from the +12v rail of a eurorack system. The regulator should probably include a heat sink given that the launchpad can draw 500mA via the USB port.

usb midi host

The novation launchpad is a class compliant usb midi device. The plexus interfaces to the launchpad via a hobbytronics usb host mini (the blue pcb in the photo). It outputs standard serial midi rx/tx directly to the teensy uart. The usb host mini is powered by 5v from the 7805 and feeds 5v at up to 500mA to the novation launchpad via USB.

teensy 3.2

A teensy 3.2 provides the smarts for the plexus. The source in the github repo can be built and uploaded using the standard (horrible) arduino ide.

gate in/out

The gate outputs are driven from the teensy output pins via a transistor to give standard 5v gate signals.

MCP4822 DAC

A pair of MCP4822 are driven via SPI by the teensy. datasheet

A MCP6004 quad opamp scales the analog output to give the correct 1v/oct. Trimmers are provided to calibrate the outputs.