Recently I’ve been revisiting an old analog modular synth prototype which I’ve had sitting on my bench in various phases for literal years. The project has focused on the challenge of designing and building a step sequencer from scratch.

Quite a few years back I saw the Music From Outer Space %TODO link varistep sequencer and thought, that can’t be that hard to build, how about designing and building my own. Well, as it turns out when you dive into the full process without a simpler prototype it does end up being quite complex.

The Overall Goals

It seemed easy enough, there needs to be: - Some control module for selecting what step was active and for interperting the user supplied speed/sync/etc. - Some way to select analog values from the potentometers - Some way to turn on the indicator LEDs - Some way to select values from the switches

The Initial Prototype

The design I came up with 16 steps which turned into 32 potentiomenters to control the notes, 16 to control the gate, and 16 leds to serve as indicators. The design I came up with had: - 16 steps - 2 analog outputs (16 rotary pots each) - 1 gate output (16 SPST toggle switches) - 1 led indicator (16 LEDS)

For outputs there would be: 1. Analog channel 1 output 2. Analog channel 2 output 3. Gate output 4. Clock output 5. Sync output

For control there would be: 1. Sequence length - 1 to 16 steps 2. Gate percentage - 0 to 100% of each step 3. Sequence speed - 0.1 to 10 Hz t FIGURE_KICAD_CIRCUIT

On top of all of this

Roadblocks

FIGURE_FRONT_PANNEL

FIGURE_BOARD_FRONT FIGURE_BOARD_BACK

FIGURE_TEST_CIRCUIT

Problems: - Too much wiring - Too many voltage buses - Difficult to test - Not enough room for control input/output

Starting The Next Revision

FIGURE_OVERALL_DIAGRAM

FIGURE_SLAVE_DIAGRAM

FIGURE_SLAVE_FRONT_PANEL

FIGURE_SLAVE_CIRCUIT

Solution: http://github.com/fundamental/avr-seq

I plan on trying to update this as the next revision evolves, but for now that’s all.