Saturday, 2 April 2011

MIDI Trigger

This box translates footswitch inputs to MIDI note on/off messages. We're using this to trigger a sampler with some special Zaardy noises on. It has three banks of three notes. The notes are played using the three footswitches on the left. The bank is selected using either the red button on top of the box or the single footswitch on the right.

It's based on an Arduino Uno, a microcontroller with handy digital inputs for the footswitches and serial out for MIDI.

The electronics is straightforward - mostly LEDs, resistors, connectors and wires:

The Veroboard sits on top of the Arduino but has to be in two parts because the pin spacing is non-standard.

Plastic boxes are not very robust for live use, but they're much easier to make holes in than metal:


The LEDs are power (red), triggered (green), bank (yellow).


To make the Arduino read the footswitch states and send the appropriate MIDI messages requires some bespoke software. The Arduino comes with a framework to help with this, so that all you have to do to read a digital input (footswitch) is:

state = digitalRead(pin);

...and state will be either HIGH or LOW.

Playing MIDI notes is also easy:

Serial.print(0x90 | (channel-1), BYTE);
Serial.print(note, BYTE);
Serial.print(velocity, BYTE);

To put this together into a complete application takes quite a lot more code, and this is what I ended up with:

The .h & .cpp files on the left are C++ classes, each performing some discrete function. They all get put together in the code on the right. The final application is downloaded to the Arduino through USB.

Future developments - Three notes are OK, but what we really need is thirteen:

This is the next project...

Friday, 1 April 2011

The Electric Violeg

Category: Rustic Homebrew

What does it do? - this is a two-stringed electric fiddle made from the amputated leg of an old table and some old guitar parts. And some Meccano. It's made entirely of things I had lying around the house and garden, the only thing I had to buy was the bow, which was the cheapest factory second I could lay my hands on. It sounds vaguely violin-ish, but in what I think is quite a good way. It's seen a good bit of usage on stage and in the studio.

This is the first attempt. The neck was much too fat to play at this stage. 

Strings anchored by strips of Meccano.

3-ply plastic strips are shielded with foil and connected to ground via the Meccano to reduce hum from the single-coil pickup. With no body to enclose the output jack and volume control, an old die-cast box was fitted to the side.

Front view of the one-a-side headstock.

Addition of crudely-carved chin-rest and corderouy-upholstered shoulder pad. 

Rear view of head, tuners mounted upside-down to conserve space.

The slimmed-down neck makes the top notes accessible to people with normal fingers.

Originally this was to be played under the chin, but it was found to be easier to have it mounted vertically on a microphone stand like a tiny 'cello. Parts of a mic clip are now permanently attached to the rear for ease of mount and dismount. It was also found to be useful to mark the notes faintly on the fingerboard with pencil, and wear a head-mounted torch when playing the instrument under stage lighting. Mark can be seen demonstrating this in the picture at the top of the article.

Future Developments? - I quite like the idea of having a quartet of these, one for each leg of the table.