What is it?

PicoStepSeq is an 8-step MIDI sequencer using a Raspberry Pi Pico, an I2C SSD1306 OLED display, a rotary encoder. and 8 "Step Switches". It outputs via USB MIDI and Serial MIDI via TRS-A 3.5mm.

Why did you make it?

I like MIDI

What makes it special?

It's cool. Also featured in MagPi Magazine #123, and in print too!

Bill of Materials

Since this is just the PCB, you'll need parts and an enclosure.

Here is a Digikey cart with most parts.

Links also included below for major parts.

For basic USB MIDI functionality:

• 1 - "picostepseq" PCB (OSHpark, also see "hardware" directory for gerbers)
• 1 - Raspberry Pi Pico (Adafruit, Digikey)
• 1 - 0.96" I2C OLED SSD1306 128x64 display (Amazon)
• w/ pins in order GND, VCC, SCL, SDA; some have GND & VCC swapped
• 1 - EC11 style rotary encoder w/ switch (Digikey, Adafruit]
• 8 - "step switch" w/ built-in LED (Adafruit]
• 8 - resistor 1k (R1-R8, 500 ohm also works) (Digikey, Adafruit]
• 1 - encoder knob ("Davies 1900" style works well, Adafruit)

For both USB + Serial MIDI, add:

• 2 - 3.5mm TRS jack, SJ-3523-SMT-TR (J1,J2) (Digikey)
• 1 - 6N138 optoisolator (U2) (Digikey)
• 1 - 1N1418 diode (D1) (on the latest version of the PicoStepSeq PCB)
• 1 - 100n capacitor (C1) (Digikey, Adafruit)
• 1 - resistor 10 ohm (R1)
• 1 - resistor 30 ohm (R2) (47 ohm also works)
• 1 - resistor 220 ohm (R3)
• 1 - resistor 4.7k ohm (R4)

And if you've not used "TRS MIDI" and have normal 5-pin DIN MIDI jacks on your gear, you'll need a few: - Type A" MIDI adapter (PerfectCircuit or Amazon)

You can attach the Pico & the OLED display how you like, but if using the 3d-printable "picostepseq_headers" case, you will also need:

• 2 - 20-pin header socket (Digikey, Adafruit)
• 2 - 20-pin header pins (Digikey, Adafruit )
• 1 - 4-pin female (same as above, break off 4-pin chunk)

The PCB surface finish is "LeadFree HASL" so if you use lead free solder, the entire project will be lead free!

Enclosure

A 3d-printable enclosure is available on Printables

The current enclosure is designed for the case where sockets are used for both the Pico and the OLED display. This is so either can be removed for other uses, so you don't have to sacrifice a Pico if you want to try this out.